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Routing in IP Environments An "internet" is a group of interconnected networks. The Internet, on the other hand, is the collection of networks that permits communication between most research institutions, universities, and many other organizations around the world. Routers within the Internet are organized hierarchically. Some routers are used to move information through one particular group of networks under the same administrative authority and control. (Such an entity is called an autonomous system.) Routers used for information exchange within autonomous systems are called interior routers, and they use a variety of interior gateway protocols (IGPs) to accomplish this end. Routers that move information between autonomous systems are called exterior routers; they use the Exterior Gateway Protocol (EGP) or Border Gateway Protocol (BGP). The Internet architecture is shown in Figure 5. Routing protocols used with IP are dynamic in nature. Dynamic routing requires the software in the routing devices to calculate routes. Dynamic routing algorithms adapt to changes in the network and automatically select the best routes. In contrast with dynamic routing, static routing calls for routes to be established by the network administrator. Static routes do not change until the network administrator changes them. IP routing tables consist of destination address/next hop pairs. In the sample routing table shown in Figure 6, the first entry is interpreted as meaning "to get to network 34.1.0.0 (subnet 1 on network 34), the next stop is the node at address 54.34.23.12." As we have seen, IP routing specifies that IP datagrams travel through an internetwork one router hop at a time. The entire route is not known at the outset of the journey. Instead, at each stop, the next router hop is determined by matching the destination address within the datagram with an entry in the current node's routing table. Each node's involvement in the routing process consists only of forwarding packets based on internal information. IP does not provide for error reporting back to the source when routing anomalies occur. This task is left to another Internet protocol: the Internet Control Message Protocol (ICMP.) ICMP performs a number of tasks within an IP internetwork. In addition to the principal reason for which it was created (reporting routing failures back to the source), ICMP provides a method for testing node reachability across an internet (the ICMP Echo and Reply messages), a method for increasing routing efficiency (the ICMP Redirect message), a method for informing sources that a datagram has exceeded its allocated

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Routing in IP EnvironmentsAn "internet" is a group of interconnected networks. The Internet, on the other hand, is the collection of networks that permits communication between most research institutions, universities, and many other organizations around the world. Routers within the Internet are organized hierarchically. Some routers are used to move information through one particular group of networks under the same administrative authority and control. (Such an entity is called an autonomous system.) Routers used for information exchange within autonomous systems are called interior routers, and they use a variety of interior gateway protocols (IGPs) to accomplish this end. Routers that move information between autonomous systems are called exterior routers; they use the Exterior Gateway Protocol (EGP) or Border Gateway Protocol (BGP). The Internet architecture is shown in Figure 5.

Routing protocols used with IP are dynamic in nature. Dynamic routing requires the software in the routing devices to calculate routes. Dynamic routing algorithms adapt to changes in the network and automatically select the best routes. In contrast with dynamic routing, static routing calls for routes to be established by the network administrator. Static routes do not change until the network administrator changes them.IP routing tables consist of destination address/next hop pairs. In the sample routing table shown in Figure 6, the first entry is interpreted as meaning "to get to network 34.1.0.0 (subnet 1 on network 34), the next stop is the node at address 54.34.23.12."As we have seen, IP routing specifies that IP datagrams travel through an internetwork one router hop at a time. The entire route is not known at the outset of the journey. Instead, at each stop, the next router hop is determined by matching the destination address within the datagram with an entry in the current node's routing table. Each node's involvement in the routing process consists only of forwarding packets based on internal information. IP does not provide for error reporting back to the source when routing anomalies occur. This task is left to another Internet protocol: the Internet Control Message Protocol (ICMP.)ICMP performs a number of tasks within an IP internetwork. In addition to the principal reason for which it was created (reporting routing failures back to the source), ICMP provides a method for testing node reachability across an internet (the ICMP Echo and Reply messages), a method for increasing routing efficiency (the ICMP Redirect message), a method for informing sources that a datagram has exceeded its allocated time to exist within an internet (the ICMP Time Exceeded message), and other helpful messages. All in all, ICMP is an integral part of any IP implementation, particularly those that run in routers.

Interior Routing ProtocolsInterior Routing Protocols or IGPs operate within autonomous systems. The following sections provide brief descriptions of several IGPs that are currently popular in TCP/IP networks. RIPA discussion of routing protocols within an IP environment must begin with the Routing Information Protocol (RIP). RIP was developed by Xerox Corporation in the early 1980s for use in Xerox Network Systems (XNS) networks. Today, many PC networks use routing protocols based on RIP.RIP works well in small environments but has serious limitations when used in larger internetworks. For example, RIP limits the number of router hops between any two hosts in an internet to 16. RIP is also slow to converge, meaning that it takes a relatively long time for network changes to become known to all routers. Finally, RIP determines the best path through an internet by looking only at the number of hops between the two end nodes. This technique ignores differences in line speed, line utilization, and all other metrics, many of which can be important factors in choosing the best path between two nodes. For this reason, many companies with large internets are migrating away from RIP to more sophisticated routing protocols.IGRPWith the creation of the Interior Gateway Routing Protocol (IGRP) in the early 1980s, Cisco Systems was the first company to solve the problems associated with using RIP to route datagrams between interior routers. IGRP determines the best path through an internet by examining the bandwidth and delay of the networks between routers. IGRP converges faster than RIP, thereby avoiding the routing loops caused by disagreement over the next routing hop to be taken. Further, IGRP does not share RIP's hop count limitation. As a result of these and other improvements over RIP, IGRP enabled many large, complex, topologically diverse internetworks to be deployed.Cisco has recently enhanced IGRP to handle the increasingly large, mission-critical networks being designed today. This new version of IGRP is called Enhanced IGRP. Enhanced IGRP combines the ease of use of traditional distance vector routing protocols with the fast rerouting capabilities of the newer link state routing protocols.EGIRPEnhanced IGRP consumes significantly less bandwidth than IGRP because it is able to limit the exchange of routing information to include only the changed information. In addition, Enhanced IGRP is capable of handling AppleTalk and Novell IPX routing information, as well as IP routing information.OSPFOSPF was developed by the Internet Engineering Task Force (IETF) as a replacement for RIP. OSPF is based on work started by John McQuillan in the late 1970s and continued by Radia Perlman and Digital Equipment Corporation (DEC) in the mid-1980s. Every major IP routing vendor supports OSPF.OSPF is an intradomain, link state, hierarchical routing protocol. OSPF supports hierarchical routing within an autonomous system. Autonomous systems can be divided into routing areas. A routing area is typically a collection of one or more subnets that are closely related. All areas must connect to the backbone area.OSPF provides fast rerouting and supports variable length subnet masks.

Integrated IS-ISISO 10589 (IS-IS) is an intradomain, link state, hierarchical routing protocol used as the DECnet Phase V routing algorithm. It is similar in many ways to OSPF. IS-IS can operate over a variety of subnetworks, including broadcast LANs, WANs, and point-to-point links. Integrated IS-IS is an implementation of IS-IS for more than just OSI protocols. Today, Integrated IS-IS supports both OSI and IP protocols. Like all integrated routing protocols, Integrated IS-IS calls for all routers to run a single routing algorithm. Link state advertisements sent by routers running Integrated IS-IS include all destinations running either IP or OSI network-layer protocols. Protocols such as ARP and ICMP for IP and End System-to-Intermediate System (ES-IS) for OSI must still be supported by routers running Integrated IS-IS.

Exterior Routing ProtocolsEGPs provide routing between autonomous systems. The two most popular EGPs in the TCP/IP community are discussed in this section.EGPThe first widespread exterior routing protocol was the Exterior Gateway Protocol. EGP provides dynamic connectivity but assumes that all autonomous systems are connected in a tree topology. This was true in the early Internet but is no longer true.Although EGP is a dynamic routing protocol, it uses a very simple design. It does not use metrics and therefore cannot make true intelligent routing decisions. EGP routing updates contain network reachability information. In other words, they specify that certain networks are reachable through certain routers. Because of its limitations with regard to today's complex internetworks, EGP is being phased out in favor of routing protocols such as BGP.BGPBGP represents an attempt to address the most serious of EGP's problems. Like EGP, BGP is an Interdomain routing protocol created for use in the Internet core routers. Unlike EGP, BGP was designed to prevent routing loops in arbitrary topologies and to allow policy-based route selection.BGP was co-authored by a Cisco founder, and Cisco continues to be very involved in BGP development. The latest revision of BGP, BGP4, was designed to handle the scaling problems of the growing Internet.

Cisco's TCP/IP ImplementationIn addition to IP and TCP, the Cisco TCP/IP implementation supports ARP, RARP, ICMP, Proxy ARP (in which the router acts as an ARP server on behalf of another device), Echo, Discard, and Probe (an address resolution protocol developed by Hewlett-Packard Company and used on IEEE 802.3 networks). Cisco routers also can be configured to use the Domain Name System (DNS) when host name-to-address mappings are needed.IP hosts need to know how to reach a router. There are several ways in which this can be done: Adding a static route in the host pointing to a router Running RIP or some other IGP on the host Running the ICMP Router Discovery Protocol (IRDP) in the host Running Proxy ARP on the router. Cisco routers support all of these methods.Cisco provides many TCP/IP value-added features that enhance applications availability and reduce the total cost of internetwork ownership. The most important of these features are described in the following section.Access RestrictionsMost networks have reasonably straightforward access requirements. To address these issues, Cisco implements access lists, a scheme that prevents certain packets from entering or leaving particular networks.An access list is a sequential list of instructions to either permit or deny access through a router interface based on IP address or other criteria. For example, an access list could be created to deny access to a particular resource from all computers on one network segment but permit access from all other segments. Another access list could be used to permit TCP connections from any host on a local segment to any host in the Internet but to deny all connections from the Internet into the local net except for electronic mail connections to a particular designated mail host. Access lists are extremely flexible, powerful security measures and are available not only for IP, but for many other protocols supported by Cisco routers.Other access restrictions are provided by the Department of Defense-specified security extensions to IP. Cisco supports both the Basic and the Extended security options as described in RFC 1108 of the IP Security Option (IPSO). Support of both access lists and the IPSO makes Cisco a good choice for networks where security is an issue.TunnelingCisco's TCP/IP implementation includes several schemes that allow foreign protocols to be tunneled through an IP network. Tunneling allows network administrators to extend the size of AppleTalk and Novell IPX networks beyond the size that their native protocols can handle.

IP MulticastThe applications that use the TCP/IP protocol suite continue to evolve. The next set of applications will include those that use video and audio information. Cisco is actively involved with the Internet Engineering Task Force (IETF) in defining standards that will enable network administrators to add audio and video applications to their existing networks. Cisco will support the Protocol Independent Multicast (PIM) standard. In addition, Cisco's implementation will provide bandwidth management, security and interoperability with the MBONE, a research multicast backbone that already exists today.IP multicasting (the ability to send IP datagrams to multiple nodes in a logical group) is an important building block for applications such as video. Video teleconferencing, for example, requires the ability to send video information to multiple teleconference sites. If one IP multicast datagram containing video information can be sent to multiple teleconference sites, network bandwidth is saved and time synchronization is closer to optimal.Suppressing Network InformationIn some cases, it may be useful to suppress information about certain networks. Cisco routers provide an extensive set of configuration options that allow an administrator to tailor the exchange of routing information within a particular routing protocol. Both incoming and outgoing information can be controlled using a set of commands designed for this purpose. For example, networks can be excluded from routing advertisements, routing updates can be prevented from reaching certain networks, and other similar actions can be taken.Administrative DistanceIn large networks, some routers and routing protocols are more reliable sources of routing information than others. Cisco IP routing software permits the reliability of information sources to be quantified by the network administrator with the administrative distance metric. When administrative distance is specified, the router can select between sources of routing information based on the reliability of the source. For example, if a router uses both IGRP and RIP, one might set the administrative distances to reflect greater confidence in the IGRP information. The router would then use IGRP information when available. If the source of IGRP information failed, the router automatically would use RIP information as a backup until the IGRP source became available again.Routing Protocol RedistributionTranslation between two environments using different routing protocols requires that routes generated by one protocol be redistributed into the second routing protocol environment. Route redistribution gives a company the ability to run different routing protocols in workgroups or areas where each is particularly effective. By not restricting customers to using only a single routing protocol, Cisco's route redistribution feature minimizes cost while maximizing technical advantage through diversity.Cisco permits routing protocol redistribution between any of its supported routing protocols. Static route information can also be redistributed. Further, defaults can be assigned so that one routing protocol can use the same metric for all redistributed routes, thereby simplifying the routing redistribution mechanism.

Serverless Network SupportCisco pioneered the mechanisms that allow network administrators to build serverless networks. Helper addresses, RARP, and BOOTP allow network administrators to place servers far away from the workstations that depend on them, thereby easing network design constraints.Network Monitoring and DebuggingWith today's complex, diverse network topologies, a router's ability to aid the monitoring and debugging process is critical. As the junction point for multiple segments, a router sees more of the complete network than most other devices. Many problems can be detected and/or solved using information that routinely passes through the router.The Cisco IP routing implementation provides commands that display the following: The current state of the routing table, including the routing protocol that derived the route, the reliability of the source, the next IP address to send to, the router interface to use, whether the network is subnetted, whether the network in question is directly connected, and any routing metrics The current state of the active routing protocol process, including its update interval, metric weights (if applicable), active networks for which the routing process is functioning, and routing information sources The active accounting database, including the number of packets and bytes exchanged between particular sources and destinations The contents of the IP cache, including the destination IP address, the interface through which that destination is reached, the encapsulation method used, and the hardware address found at that destination IP-related interface parameters, including whether the interface and interface physical layer hardware are up, whether certain protocols (such as ICMP and Proxy ARP) are enabled, and the current security level IP-related protocol statistics, including the number of packets and number of errors received and sent by the following protocols: IP, TCP, User Datagram Protocol (UDP), EGP, IGRP, Enhanced IGRP, OSPF, IS-IS, ARP, and Probe Logging of all BGP, EGP, ICMP, IGRP, Enhanced IGRP, OSPF, IS-IS, RIP, TCP, and UDP transactions The number of intermediate hops taken as a packet traverses the network Reachability information between nodes SummaryIP is one of over 20 protocols that can be simultaneously routed and bridged by any of Cisco's routers. Cisco has added features to its IP implementation that optimize the performance of Cisco routers in larger, enterprise-wide internetworks.

Routing Protocol Overview IP routing protocols have one primary goal- to fill the IP routing table with the current best routs it can find. A routed protocol is a protocol with OSI Layer 3 characteristics that define logical addressing and routing. The packets defined by the network layer (Layer 3) portion of these protocols can be routed. Examples are IP and IPXThe term routing type refers to the type of routing protocol, such as link-state and distance vector.IP routing protocols fill the IP routing table with valid, (hopefully) loop-free routes. Although the primary goal is to build a routing table, each routing protocol has a very important secondary goal of preventing loops. The routers added to the routing table include a subnet secondary goal of preventing loops.All routing protocols have several general goals:

To dynamically learn and fill the routing table with a route to all subnets in the network.

If more then one route to a subnet is available, to place the best route I the routing table.

To notice when routes in the table are no longer valid, and to remove those rous from the routing table.

If a route is removed for the routing table and another route through another neighboring router is available, to add the route to the routing table.

To add new route, or to replace lost routs with the best currently available route, as quickly as possible. The time between losing the route and finding a working replacement is call convergence time.

To prevent routing loops.

Comparing and Contrasting IP Routing ProtocolsRouting protocols can be categorized in several ways. One distinction is whether the protocol is more useful between two companies or inside a single company. Only one IP routing protocol that is popular today, The Border Gateway Protocol (BGP), is designed specifically for use between two different organizations. In fact, BGP distributes routing information between ISPs worldwide today and between ISPs and their customers as need be.

Routing protocols that are best used to distribute routes between companies and organization, such as BGP, are called exterior routing protocols.

Routing protocols designed to distribute routing information inside a single organizations are called interior routing protocols.

Major Comparison Points between Interior Routing ProtocolsPoint of ComparisonDescription

Type of routing protocolEach interior routing protocol covered in this chapter can be characterized based on the underlying logic used by the routing protocol. This underlying logic often is referred to as the type of routing protocol.

The three types are Type of routing protocol:

DISANCE Vector

Link State

Hybrid

Full/Partial updatesSome interior routing protocols send their entire routing which are called full routing updates. Other routing protocols send only a subset of the routing table in updates, typically just the information about any changed routs. This subset is referred to as partial routing updates Partial routing updates. Partial routing updates require lessoverhead in the network.

ConvergenceConvergence refers to the time required for router to react to changes (for example, link failures and router failures) in the network, removing bad routes and adding new, better routes so that the current best routes are in all the routers routing tables.

MetricThe Metric refers to the number value that describes how good a particular route is. The lower the value is, the better the route is. Some metrics provide a more realisticPerspective on which routes are truly the best routes.

Support for VLSMVariable-length subnet masking (VSLM) means that, in a single Class A,B or C network, multiple subnet masks can be used. The advantage of VLSM is that it enables you to vary the size of each subnet, based on the needs of the subnet. A mask allowing a much larger number of IP address can be used on each LAN-based subnet. Some routing protocols support VLSM, and some do not.

Classless or ClassFull Classes routing protocols transmit the subnet mask along with each route in the routing updates sent by that protocol.

Classfull routing protocols do not transmit mask information. So, only CLASSLESS routing protocols support VSLM.

To say that a routing protocol is classless is to say that it supports VLSM, and vice versa

Routing through the internet with the Border Gateway ProtocolBGP advertises only routing information to specifically define peers using TCP. By using TCP, a router knows that any routing updates will be re-sent if they happen to get lost in transit.BGP uses a concept called autonomous system when describing each route. An autonomous system (AS) is a group of devices under the control of a single organization-on other words, that organization has autonomy for the other interconnected parts of the Internet. An AS number (ANS) is assigned to each AS, uniquely identifying each AS in the Internet. BGP includes the ASNs in the routing updates to prevent loops.BGP does not use a metric like internal routing protocols. Because BGP expects to be used between different ISPs and between ISPs and customers, BGP allows for a very robust set of alternatives for deciding what route to use; these alternatives are called policies. Routing policy can be based on the fact that an ISP might have a better business relationship with a particular ISP.

Interior Gateway Routing Protocol (IGRP)

IGRP is a Cisco-proprietary IP routing protocol created by Cisco more than 10 years ago. Cisco created IGRP to provide a better distance vector protocol to its customers, as compared with RIP-1

The most obvious difference between RIP-1 and IGRP is the metric. IGRP advertises up to five parameter that describe the metric for each route, although, practically, only two ever are used- BANDWITH and DELAY.The Bandwidth part of this more complex metric describes the constrained link speed. For instance, if a route to a subnet contained all Fast Ethernet links, the bandwidth in the update would be 100 Mbps; however if a single 56kbps link were in the path, the bandwidth would be listed as 56 kbps. The delay components includes a cumulative number- fro instance, a route going over ten Fast Ethernet links would have its delay part of the metric ten times bigger then a route with a single 100-mbps line in the path.IGRP calculates the metric based on a mathematical formula.

Distance Vector Protocols Compared

FeatureRIP-V1RIP-2IGRPUpdate timer for fullRouting updates30 seconds30 seconds90 seconds

MetricHop countHop countFunction of bandwidth and delay (default), Can include load, and MTU.Supports VLSMNoYesNo

Infinite-metric value16164,294,967,295

ConvergenceSlowSlowSlow

Link-State Protocols: OSPF and Integrated IS-ISLink-State and distance vectors share a common goal to fill the routing tables with the current best routes. They differ significantly in how the each accomplish the task. The largest difference between the two is that distance vector protocols advertise sparse information; in facet, distance vector protocols know only that other router exist if the other router broadcasts a routing update to them.When a distance vector protocol in a router hears a routing update, the update says nothing about the routers beyond that neighboring router that sent the update.Conversely, LINK-STATE protocols advertise a large amount of topological information about the network, and the routers perform some CPU-intensive computation on the topological data. They even discover their neighbors before bothering to exchange routing information.To figure out the current best routs, a router process the LINK-STATE topology database using an algorithm called the Dijkstra Shortest Path First (SPF) algorithm. This detailed topology information, along with the Dijkstra Algorithm, helps link-state protocols avoid loop and converge quickly.Link-State protocols prevent loops from occurring easily because each router essentially has a completed map of the network. If you take a trip in your car and you have a map, you are a lot less likely to get lost than someone else who is just reading the signs by the side of the road. Likewise, the detailed topological information, helps link-state protocols easily avoid loops. As you will read later, the main reason that distance vector protocols converge slowly are related to the loop-avoidance features. With link-state protocols, those same loop-avoidance features are not needed, allowing for fast convergence-often in les than 10 seconds. Open Shortest Path First (OSPF)OSPF is the most popular LINK-STATE IP routing protocol today and is likely to be the most popular one for some time. The basic operation of OSPF differs from that of the distance vector protocols. One difference relates to how and when OSPF actually sends routing information. A router does not send routing information with OSPF until it discovers other OSPF-speaking routers on a common subnet.

The following list gives you some idea of the process:1) Each router discovers its neighbors on each interface. The list of neighbors is kept in a Neighbor table.

2) Each router uses a reliable protocol to exchange topology information with its neighbors.

3) Each router places the learned topology information into its topology database.

4) Each router runs the SPF algorithm against its won topology database to calculate the best routers to each subnet in the data base.

5) Each router places the best route in each subnet into the IP routing table.

Link-State protocols do require more work by the routers, but the work is typically worth the effort. A router running a link-state protocol uses more memory and more processing cycles then do distance vector protocols. The topology updates require a large number of bytes to describe the details for every subnet, every router, and which routers are connected to which subnets. However, because OSPF does not send full updates on a regular short interval (like RIP), the overall number of bytes sent for routing information is typically smaller. Also, OSPF converges much more quickly then do distance vector protocols and fast convergence is one of the most important features of a routing protocol.OSPF uses a concept called cost for the metric. Each link is considered to have a cost; a routes Costs is the sum of the cost for each link. By default, Cisco derives the cost value for a link form the bandwidth, so you can think of the metric as being based on cumulative link bandwidth.(IGRP metric is based on delay and bandwidth, but it does not treat bandwidth as a cumulative value; it considers only the slowest link in a path.)Routers use Hellos to Discover Neighbors then they can Exchange Routing Information: Protocols which use Hellos to Discover Neighbors are :OSPF and EIGRP only

OSPF and EIGRP only send PARTIAL Routing Updates with its Neighbors when there is a change in the Network.

EIGRP Multicast address is 224.0.0.10The Following list point out some of the key features of OSPF: Converges very quickly form the point of recognizing a failure, it often can converge in less than 10 seconds.

Supports VLSM

Users short Hello messages on a short regular interval (the Hello interval) which the absence of Hello messages indication that a neighbor is no longer reachable.

Sends partial updates when link status changes and floods full update every 30 minutes. The flooding, however, does not happen all at once, so the overhead is minimal

Users cost for the metric.

Integrated IS-ISOSI defines a network layer protocol called the Connectionless Network Protocol (CLNP). It also defines a routing protocol- a routing protocol used to advertise CLNP routes, called Intermediate System-to-Intermediate System (IS-IS). IS-IS advertises CLNP routes between intermediate systems, which is what OSI calls routers.Later in life, IS-IS was updated to include the capability to advertise IP routes as well as CLMP routes. To distinguish it form the older IS-IS, this new updated IS-IS called Integrated IS-IS. The word integrated identifies the fact that the routing protocol can exchange routing information for multiple Layer 3 routed protocols. Integrated IS-IS has an advantage over OSPF because it supports both CLNP and IP route advertisement, but most installation could not care less about CLNP.

IP link State Protocols Compared

FeatureOSPFIntegrated IS-ISPeriod for individual Re-flooding of routing Information30 minutes15 minutesMetricCostMetricSupports VLSMYes Yes

ConvergenceFastFast OSPF uses 10^8 / bandwidth to Determine the Cost of the Route using the following Command:IP Bandwidth 64000- 10^8/64000 = 16 The Cost of this route Would be 16 in the Routing table.Balanced Hybrid Protocols:Enhanced IGRPEIGRP does not use distance vector or link-state logic, but instead it uses a whole new category of routing protocols, other similar to distance vector protocols, and yet other unlike either of the two. Cisco sometimes categorizes EIGRP as a placed hybrid protocol, so you should remember the term.The internal working of EIGRP depend on an algorithm called theDIFFUSING UPDATE ALGORITHM (DUAL).DUAL require far less processing then the computation intensive Dijkstra SPF algorithm.DUAL defines a method for each router not only to calculate the best current route to each subnet, but also calculate alternative routs that could be used if the current route fails. An alternative route, using what DUAL calls a feasible successor route, is guaranteed to be loop free. So, if the current best route fails, the router immediately can start using the feasible successor route instead so that convergence can happen very quickly.

The following list point out some of the key similarities to some of the other protocols covered so far: Like OSPF the Integrated IS-IS, it converges quickly, often in less than 3 seconds after a failure is recognized.

Like OSPF, EIGRP discovers neighbors before sending them routing information.

Like RIP and IGRP, EIGRP requires very little design effort. (Link-State protocols require some design work in medium to larger networks.

Like IGRP, EIGRP is Cisco proprietary.

Like IGRP, EIGRP does not send full updates on periodic interval, but rather sends partial updates only as links to routers go u and down.

Like Link-State protocols, EIGRP builds some topology tables in addition to the IP routing table.

Comparing Link-State and Distance Vector ProtocolsFeatureLink-State(OSPF,EIGRP(HYB))Distance-Vector (RIP-IGRP)Convergence timeFAST Slow Because of Loop Avoidance Features Loop AvoidanceBuilt into the Protocol Split Horizon, Hold-down Timers Memory and CPU RequirementsCPU and Memory Intensive Low Processing is needed Processing

Requires Design EffortYESNOFor large Networks

Advanced Routing Protocol Topics***Route SummarizationRoute (manual) summarization (RS) reduces the size of routing table while maintaining routes to the entire destination in the network. Also improves convergence time

The routing protocol must support VLSM when the network uses route summarization.OSPF- EIGRP-RIPv2 VLSM means that in a single class A, B, C network, more than one subnet mask value is used.

Command for route summarization:Router (config) # Interface serial 0/0Router (config-int) # ip summary-address eigrp 1 10.2.0.0 255.255.0.0

This caused the entire 10.2.0.0 network member to be advertised as 10.2.0.0 instead of advertising:

10.2.1.010.2.2.010.2.3.0 It will only advertise 10.2.0.0 255.255.0.0 for all Subnetworks.

Router# show ip route

Route (manual) summarization can only be supported by Classless routing protocols, because the summaries in effect require that subnet mask information be included inside routing protocols updates.

Autosummarizaion is on by default, and can be disabled for EIGRP, But Autosummarizaion is not available for OSPF.

Router summarization allows summarizing route into any larger grouping, but Autosummarizaion only summarize routes as entire Classful networks (A, B or C class networks).

Finally, because RIP version 1 and IGRP are ClassFul, they cannot perform manual route summarization, which requires a ClassLess router protocol.

When a default route is configured on a router, and parts of the ClassFul network of the destination IP address are in the routing table, then the IP ClassLess command determines if the default route is used.

With IP ClassLess command configured, the packet would be forwarded using the default route because it would not care if there were any other routes in the routing table in the same subnet.

With No IP ClassLess command configured since there are some routes ip address in the same subnet but not matching it would discard the packet because of the other routes in the same SubNetwork with similar routes even though they do not match.

Variably Subnetted- This phrase means that more than one subnet mask is used in the network. Only routing protocols that support VLSM (ClassLess) can use Route (manual) Summarization EIGRP supports VLSM When using RS directly connected routes are not Summarized because they are connected.

Null 0 is used to discard packets going to routes not summarized.

When a network uses more than one value in its prefix /16, /24, /23, /33 on its different routes it is said that that network is using VLSM.

VLSM requirements Subnets Do Not Over Lap only one interface per subnet. The routing protocol must support VLSM

Protocols that support VLSMRIP1NOIGRPNORIP-2YESYES Protocols send mask and Prefix (/15)EIGRPYESinformation in Routing updates and they OSPFYES Support Route Summarization.ClassLess and ClassFull routing ProtocolsClassful- routing protocols do not transmit the mask information along with the subnet number.ClassLess - routing protocols DO transmit mask information.ClassFul - Routing protocols Forgets to send mask information is it assumed all are the same.ClassLess Routing protocols Leaks/Sends out the mask information to other routers.Autosummarization Rip & IGRP - Perform Autosummarization by default it is a feature of ClassFull Protocols.

Rip v2 & EIGRP Autosummarization can be turned on or off.

When a router has interfaces in more than one Class A,B,C network, It advertises a single route fort he entire Class A,B,C network. This feature is called Autosummarization.

Autosummarization must have a continuous set of sub networks for it to be able to work with ClassFull networks.

Routing ProtocolsClassfull Protocols (Forget subnet #) ClassLess (learn/Send Subnet information)Protocol ValueRIPv1OSPF89IGRPEIGRP88SLSMRIP v2

Formula for calculating Host members ClassFull Protocols use 2^2-2

ClassLess Protocols Use 2^2

This only affects the Host values/members.

Static Route Command:Router# ip route 10.1.2.0 255.255.255.0 10.1.128.252 Subnet Number Outgoing InterfaceOrRouter# ip route 10.1.2.0 255.255.255.0 Serial 0Subnet Number Outgoing Interface To get to 10.1.2.0 you have to use 10.1.128.252 (serial ip address) route

To check which Routes are in the routing Table you will have to use the Command

Router# show ip route This will show you all the routs in the rouging table static, IGRP, RIP, EIGRP, and OSPF routes on a router.

The purpose of configuring Static routes, as well as RIP and IGRP is to add Routes to a routers routing table.

Distance Vector Concepts Vector means Send routing information in your update.

Distance Vector protocols work by having each router advertise all the routs they know out all there interfaces. Switches use Cost to determine the best Root for STP

Routers use Metric to determine the best route

Distance Vector ProtocolsMetric UsedRIPHop countIGRPBandwidth, delay, load, MTU, Default values are used

Distance Vector Protocols: RIP and IGRPDistance vector protocols advertise routing information by sending messages, called routing updates, out the interfaces on a router. These updates contain a series of entries, with each entry representing a subnet and metric. The metric represents how good the route is from that routes perspective, with a smaller number being a better route.Any routers that receive a copy of a distance vector routing update receive that information and possibly add some routes to their routing table. The receiving router adds the routes only if the routing update described a route to a subnet that it did not already know about or if it described a route that already was known, but the newly learned route has a better (lower) metric.

The following list formalizes the basic distance vector logic and introduces a few important concepts:

Routers add directly connected subnets to their routing tables, even without a routing protocol.

Routers send routing updates out their interfaces to advertise the routes that this router already knows. These routes include directly connected routes as well as routes learned from other routers.

Routers listen for routing updates form their neighbors so that they can learn now routers, how good the route is: lower metric routes are considered better routes.

When possible, routers use broadcasts or multicasts to send routing updates. By using a broadcast of multicast packet, all neighbors on a LAN can receive the dame routing information in a single update.

If a router learns multiple routs to the same subnet, the router chooses the best route based on the metric.

Routers send periodic full updates and expect to receive periodic updates form neighboring routers.

Failure to receive updates form a neighbor in a timely manner results in the removal of the routes previously learned form that neighbor.

A router assumes that, for a route advertised by router X, the next-hop router in that route is Router X

Remember to use the IP Address of the other router interface ip address with IP-Addressing.

All Protocol updates are received from the other Router Interface IP Address NOT the Router interfaces on the ROUTER which you are looking at.

Routing Information Protocol Version 1 (RIPV1)RIP uses hop count for a metric. That means that, from an individual routers perspective, if there are two routers between itself and a subnet, its metric for that subnet is 2.List of RIP-V1 features can help you compare RIP-1 to some of the other IP routers in protocols: Based on distance vector Logic

Uses hop count for the metric

Sends periodic full routing updates every 30 seconds

Converges slowly, often taking 3 to 5 minutes

Does not support VLSM, also making it a Classful routing protocol

RIP & IGRP default Values FeatureRIP valuesIGRP valuesRoute update timerEvery 30 sec.Every 90 sec.MetricHop CountDelay, Bandwidth, MTU, load, ReliabilityHold down Timer180 sec280 secFlash Triggered updates yesyesMast sent in updateNONO (ClassFull Protocol)Infinite Metric (Route Poison Value)164,232,232,232

Neither RIP or IGRP support VSLM

Distance Vector Loop-Avoidance Features Split horizon- The routing protocol advertises out an interface only if they were not learned form updates entering that interface. Split horizon with Poising Reverse (Poison Reverse)

Route Poising values in there metric valueProtocol Metric Poison ValueRip 16IGRPMore then 4 billion (4,000,000,000)RIP router commandsRouter# router ripRouter# Network 130.25.0.0------------------ (Full A, B, C class networks only)IGRP CommandsRouter# router IGRP 7(AS number) -----Autonomous System number needed-***Router# network 130.25.0.0 ------------------(Full A, B, C class networks only)The network command matches one or more interfaces on a router. For each interface, the network command causes the router to do three things:1) The router Broadcasts or Multicasts routing updates out an interface.2) The router listens for incoming updates on that same interface.3) The router, when sending an update, includes the subnet of that interface in the routing update.

Rip uses the Network number not the subnet number the IOS will change it to the network number if it is entered.

By default RIP configured interfaces Send out RIP updates using RIP v 1 and it can Receive RIP V1 AND RIP V2 by default.

You can check to see what Routing Protocol is being used and the parameters by using the

Command:>Show IP protocolsClass Subnet numberNetwork numberA10.1.2.310.0.0.0B172.16.1.1172.16.1.1C199.1.1.1199.1.1.0 Router RIP [or, IGRP, OSPF, EIGRP] command puts the router in that configuration mode.

IGRPAS- Autonomous System refers to a network that is within the control of a single company or org. Router # Show Ip route------- Is used to list all routes in a routers routing table.

IGRP Router interfaces must use the same AS number. Router# router IGRP 23 (AS number)Example of the show command#Show IP RouteI 10.1.4.0 [100/8539] via 10.1.2.14 Outgoing Interface[100/8539]= [administrative distance/metric] When using more than one Routing protocol Administrative distance is used to determine which routing Protocol has the best believable distance (shortest path to the destination)Routing ProtocolAdministrative distance IGRP100Rip 120 The lower the Administrative distance the more the route is trusted.

IGRP Uses bandwith command on each interface to determine the interface bandwidth.

Debug Commands for RIP and IGRPRIP Debug command:Router# debug IP ripIGRP debug Command:Router# debug ip IGRP transactionsRouter# debug IP IGRP eventsBoth use this command to show all routes:Router# show IP routeTo turn off debugging use:Router# no debug allTo show routing Protocols use: Router# Show IP Protocols

Distance Vector Routing protocols only send ClassFull information in there Routing Commands.Rip uses Full network only for its Network command:#Router RIP#Network 10.0.0.0 (For a Class A network) This command will put the interface Network in the routing table and broadcast it to other routers. Interfaces which send routing information also can receive routing informationIP addressRangeNetwork bitsMaskClass A network 10.0.0.01 1268255.0.0.0Class- B Network172.16.0.0128 19116255.255.0.0Class C Network198.168.1.0192- 22324255.255.255.0Rip- Only uses Hop Count to figure out what to put in the routing table. Rip will only put the route with the lowest metric/hop count in the routing table. If there are two routes with equal metrics Rip will put all equal metric routes in the routing table as long as the table has Max path command configured (default is 4 paths). TCommand to enable IGRP routing :#Router IGRP 2#Network 172.16.0.0 This command sets up IGRP to broadcast its Network and receive other network on that interface.

The AS (2) is needed for all IGRP configuration and all routers must match.

IGRP Uses Bandwidth & Delay Metric to decide on which routs to put in the routing table. If there are multiple routes with equal Metrics IGRP will add all routes with the same metric to the routing table. Max-path command is default to 4 max is 6.IGRP Displays 2-4 (Max is 6) different Equal Metric routs based on the Maximum Paths command. If there are more then 2 paths to a network with equal metrics both will be listed under the route.Commands:Debug IP IGRP transactions Shows the details of the routing updates.Debug IP IGRP events -Shows simply mentions that routing updates have been received.Show IP protocol -Lists several important details about the routing protocol:Update timer is listedTime remaining until the next routing update is sent.Neighbors are listed which routing information was received. To check update just use Show IP Protocols and it will tell you the status of the routing protocol.

Rip -Routing Protocols would put Routs D-B only because Rip uses hop count to figure its metric. If Rip had multiple routes to the same subnet network RIP would load balance the packets.

IGRP- Routing Protocol would put Rout D A B and D C B as a route to be because the Bandwidth and Delay would chose the 1.544 (T`1) link is much faster then the 64k link.Since both routes have the same metric both routes would be put in the routing table. Up to the default of four would be put in the routing table and the max is 6 if set up with the max-paths x command.

IF IGRP had multiple routes with the same metric IGRP would balance the traffic based on the metric of the route.

Link State Routing Protocols and OSPF concepts Link state Protocols Advertise a large amount of topological information about the network, the routers perform some CPU intensive computation on the topological data. They even discover their neighbors before exchanging routing information.

Link State Protocols - must calculate the metric instead of simply being told the metric in the receiving update.

Link state protocols Topology information learned by a router includes a Cost associated with each link in the network.

The algorithm used to calculate the routes with Link State protocols is called the Shortest Path First (SPF) algorithm or it is called Dijkstra SPF algorithm or simply Dijkstra after its inventor.

Routers using Link State Protocols Discover neighbors in a common Subnet

Exchange topology database information by sending several types of packets: Link State Updates (LSU) Database description packets (DD) Link State advertisements (LSA)

Link State Protocol OSPF- Open Shortest Path FirstOpens shortest path First (OSPF) converges much more quickly then do distance vector protocols.To uniquely identify each router in the database, OSPF uses a concept call the OSPF router ID (RID)The end goal is to be able to uniquely identify each router in the data base, and to make sure that no two routes have the same RID to avoid confusion. OSPF has each router use one of the routes IP addresses, because the routes should not use duplicate IP addresses.1) Loop Back address2) Highest IP address on a working interface -----------*******OSPF can be restarted with the command:Router# clear ip ospf processOSPF uses Hello multicasts packets out each interface and hopes to receive Hello packets form the other routers connected to those interfaces.To become a OSPF NeighborRouter on the same subnet must agree about sever of the parameters exchanged in the Hello. Subnet mask used on the subnet

Subnet number (as derived using the subnet mask on each routers interface ip address.

Hello Interval

Dead Interval

OSPF area ID

If any one of these parameters differs, the routers DO NOT BECOME NEIGHBORS.

Hello Packets are used between OSPF routers: If none are received it is called Dead Interval

Dead intervals defaults to 4 times the Hello interval

Cisco routers default to a Hello interval of 10 seconds and a dead interval of 40 sec. (4*10) which means the link is Dead.

Reducing OSPF Overhead Using Designated RoutersDesignated Router (DR)- Must be elected before database description (DD) packets, containing LSA, can be exchanged between routers. DRs are always required on LAN and some times if frame Relay or ATM is used. Point to Point Routers No DR is needed.

LANs with multiple Routers DR is needed.

Using DR reduces the amount of update traffic between routers only the DR sends out updates DD and LSU packets.NBMA- Non Broadcast Multi-access such as Frame RelayCommand for Network Type is: Router# ip ospf network Backup DR (BDR) is used when the DR fails. DR and BDR are called DROTHERABR Area Border Router Area Border Router (ABR) are used to separate network areas to make the advertisements smaller in large networks.

Area Border Router (ABR) is used to describe a router that sits in both areas. An ABR has the topology database for both areas and run SPF when links change status in either area. Area 0 is considered the back bone area

OSPF designs are hierarchical

Link States uses SPF it is also called Dijkstra Algorithm or Dijkstra.Link State first must discover its neighbors by finding routers which share the same Link State protocol and share the same subnet. Once they find their Neighbors they start to send copies of the Topology Data Base and then the router runs the SPF algorithm to calculate the routs needed to be placed in the routing table,Information exchanged:LSU Link State UpdatesDD- Data Base description (has the LSA and Topology Data Base information)LSA- Links state advertisements (Information on subnet number & Mask information). OSPF uses a reliable protocol to exchange routing information about the subnets.Link State protocols:OSPFEIGRP (Hybrid)ISISLinks State Protocols use tables:Neighbor TableTopology Data BaseRouting TablesNeighbor Table Lists a table of Link State NaborsTopology Table holds the Topology information (LSA) with its neighbors. SPF is used to calculate the best routes to a subnet.Links State converges much faster than Distance Vector protocols.OSPF- Topology Database consists of subnets (called links) which contains lists of routers, along with the links (subnets) to which each router is connected. This is what Link State (OSPF) Protocols use to configure their routing table for the best routs to all subnets.OSPF Routers use the concept of OSFP router ID (RID) to identify each router.Route ID is found by doing the following:1) Highest Loopback interface is found2) If no Loopback is found the highest up & up interface is used.

OSPF Sends a Multicast Hello out 224.0.0.5 to find all OSPF Speaking routers. Hello packets have an IP packet protocol of 89 and it is placed in the header of the multicast to 224.0.0.5. Hellos are used to discover Neighbors.

OSPF router listens for Multicasts on 224.0.0.5 for hello packets.

Hello packets have the following information in them:-Header 89-Sending routers RID-Area ID-Hello Interval -Dead interval-Designated Router (DR)-Backup Designated Router (BDR)-A list of neighbors that the sending router already knows about on the subnet. Once a router sees its own RID in a Hello received from a neighbor it is said to be in Two-way communication state with that neighbor.For OSPF routers to become neighbors they must have the following same information configured in there Hellos:Subnet numberSubnet MaskArea IDHello Interval Dead interval If any one of these differs they cannot become neighbors and exchange topology information.Designated Routers (DR) must be elected for the subnet before Database Description (DD) packets are sent.

Database Description Contains :Topology Information And LSA (Link State Advertisements) When a Designated Router has been chosen all updates are sent from and to the (DR). The DR distributes the routing Information. The DR sends the DD and LSU packets to the other routers. Point to Point Links do not need a DR

Multipoint Network Need DRs

DR are used to stop the over loading of the subnets with too much OSPF traffic.

LAN interfaces default to OSPF broadcast which requires a DR

IP OSPF network command is used with the frame relay to determine the type of OSPF used there are Five types.

DRs also needs a Backup Designated Router (BDR) just in case the DR goes down or fails.The election of the Designated router is based on the following criterias:1) The router sending the Hello with the Highest Priority setting becomes the DR.

2) If there is a tie the router with the highest RID wins.

3) Second Up & Up router with the second highest priority becomes the BDR.

4) A Priority setting of 0 means the router will never be a DR.

5) Priority valid Range is 1 through 255

6) If a new router is added to the subnet with a higher Priority value then the present DR the router does not immediately take over a DR, but must wait until the DR & BDR fail If there is no DR and there is a Two-Way communication between two routers a Unicast is sent between them which includes routing updates between neighbors.

OSPF uses a Process ID, They do not have to match in order for router to communicate (send and receive hellos).

OSPF Router Commands: Router # Router OSPF 1 Process ID Wildcard MaskRouter # Network 10.0.0.0 0.255.255.255 area 0 Area # must match in order to communicate Wild card Number: 0.255.255.2550 = Care about the number in that place255 = Do not care about the number in that placeRouter # Network 0.0.0.0 255.255.255.255 area 0 = Match all IP addressThis will match all IP address in all Networks.OSPF Commands:Router# debug IP OSPF eventsRouter# show ip route Show all Routes in routing tableRouter# show ip route ospf Shows only OSPF routes learnedRouter# show ip ospf interface Shows only ospf interfacesRouter# debug OSPF Hello Lets you view transactions between routers OSPF Uses Cost to determine the metric for each route. You can set the cost with the following command:Router# ip OSPF cost x OSPF NON-DRs send updates to the DR & BDR using 224.0.0.6 Multicast Address.BDR (Backup Designated Route)- only listens for and receives updates, so it is ready to take over for the DR, but the BDR does not forward updates to Non-DRs.Once a router has Exchanged its Entire Linkstate Data Base with a Neighbor, it Transitions into a State called FULL-STATE. (Also known as being ADJENCENT) Show IP OSPF Neighbor Command Lists one or more Neighbor in a FULL-STATE = being ADJECENT. OSPF considers a Neighbor in the FULL-STATE to be fully ADJACENT.

Non-DR can be in a FULL-STATE with DR or BDR when the exchange updates with each other.

NON-DR can only form TWO way states with other NON-DRsOnce a Router has received a Full Database exchange from a Neighbor, it can run the SPF algorithm and update the Routing Table. Avoidance is build into the SPF Algorithm whenever a Link Fails all the Neighbors are updated.

OSPF convergence takes about 5 Seconds after the Failure is detected.OSPF Areas are used to create smaller OSPF Areas so the Routing Advertisements are smaller which save some of the memory and process on a Router.AREA Border Router (ABR) are used to separate areas which can also save memory and processing on Routers in its tables it holds Routes on more than one area.

OSPF sends Routing up dates by using the following information

Non-Designated Routers (DR-Other) Sending updates on 224.0.0.5DesignatedRouters

Designated Non-Designated Routers (DR-Other)Routers(DR)Sending updates on 224.0.0.6

EIGRP Link state protocolEIGRP uses three routing tables. Show EIGRP neighbor table :

Router# show ip eigrp neighbor

Show EIGRP Topology Table:

Router# show ip Topology

Show EIGRP Routing Table:

Router# Show IP route EIGRP OrRouter# Show IP route EIGRP- Supports IP, IPX, AppleTalk if configured for all three Layer 3 protocols there would be 9 different tables.

Router# show IPX EIGRP TopologyRouter# show IP EIGRP TopologyRouter# show AppleTalk EIGRP Topology EIGRP- Uses Hello packets messages to exchange messages. EIGRP Must use the same AS number valid range is 1 through 65,535.

EIGRP uses RTP Reliable Transport Protocol (RTP) to send updates.

Sends Multicast on IP address:224.0.0.10 Or to a Unicast address.

224.0.0.10

Updating the Routing Table while avoiding loops EIGRP- Uses Feasible Successor to take over if a route should fail by using

Query Response process to confirm that no loop exists before an attentive route can be used.

EIGRP- Calles the best route (the route with the lowest metric) the

Successor.

Any back up routs that could be used with out causing a loop are called:

Feasible Successors. EIGRP uses the DUAL algorithm Diffusing update Algorithm.

Dual sends out queries when a route fails. When it finds a loop free route to the subnet in questionWhen Dual find it/one adds it to the routing table. EIGRP only works with CISCO equipment.

The Default time for the EIGRP Hello messages is: Every 5 seconds on a point to point network.

60 seconds on Frame Relay and Multi Point.

EIGRP Sends Multicast on IP address:224.0.0.10 Or to a Unicast address.OSPF Sends Multicast on IP address:224.0.0.6 Between the DR and BDR ONLY!!!224.0.0.5 To all other OSPF routers using this IP address. Only the DR sends out on the 224.0.0 for updates Neighbors just listen for the updates.Show ip route valuesD- EIGRPC ConnectedI- IGRPS StaticR- Rip*- Means this is the default route EIGRP and IGRP are CISCO Proprietary Protocols (They only work on CISCO Equipment).

EIGRP only sends Routing information once to a Neighbor and only sends Routing information when there is an UPDATE or a Change in the NETWORK.

IGRP Sends the entire Routing Table every 90 Seconds.

EIGRP Can Send/Exchange routing information for Multiple protocols like NOVELL, IPX, APPLE Talk in addition to IP Layer 3 Protocols.

EIGRP- Router discover other EIGRP Routers that are attached to the same subnet they then form a NEIGHBOR RELATIONSHIP with each other.

Each Router Keeps a List/Table of Neighbors in its EIGRP Neighbor Table. (HELLOs are used to discover Neighbors)

EIGRP- Then exchanges Network Topology information with Known Neighbors, Placing the information in the EIGRP Topology TABLE. EIGRP- Analyzes the topology information, and Puts the Lowest Route with the Lowest Metrics into the Routing Table.Commands: Show IP EIGRP Neighbor Show IP EIGRP TOPOLOGY Show IP route Show IP Route EIGRP (Shows only Successor Routs) Show IPX EIGRP Show APPLE_TALK EIGRPEIGRP Hellos are sent every 5 seconds LANsOn LANs every 60 seconds on WANS like Multipoint Frame Rely Networks.EIGRP Sends Multicast with updates on 224.0.0.10 updates are topology information about the Network.-224.0.0.10 is used when it is to be sent to many EIGRP Routes. A Unicast is sent when it is just one Neighbor.-Hellos are sent to 224.0.0.10 Multicast address.-Updates are sent using Reliable Transport Protocol (RTP).-RTP is used by EIGRP to better avoid Loops.EIGRP Avoids Loops by keeping some basic Topological Information but not All/Full Table.EIGRP When there are Multiple Routes to the same Subnet, it puts the Best Routs in the Routing table.EIGRP- With a Feasible Successor can be used immediately after a Route Failed.-Without a Feasible Successor (FS) EIGRP uses QUERY & REPONSE process to confirm that no Loop exists before it can be used.EIGRP Successor and Feasible Successors with Successor and Feasible Successors there are no Loops, So the Feasible Successors can be used when the Successor Route fails if there are NO Feasible Successors then a new Route must be found with Query and Response.EIGRP Uses BANDWIDTH and DELAY to figure the best route by using them to configure the METRIC. The lower the METRIC the better the ROUTE is.EIGRP Uses DUAL (Diffusing Update Algorithm (DUAL)). To calculate new routes without LOOPS DUAL sends out QUERY and REPLY to FIND LOOP FREE routs when there is no Feasible Successor in the routing table.CommandsIP OSPF Cost x (X= Sets the cost of an interface)Bandwidth x (X sets the Bandwidth used for Route Selection)EIGRP Uses the range 1 65,535 as the Range of Valid Autoxxxxxx (AS) number.CommandRouter EIGRP X ------------------( X= AS number)OSPF When setting up the Network Command for the Router OSPF command it is Preferred to use a STATIC wild card.CommandShow IP INT Brief10.1.1.1 255.255.2555.0Router OSPF 1Network 10.1.1.10.0.0.0 Area 1**** Should be used instead of a Network 10.0.0.0 255.255.255.2555 area 0Used with Link State Routing Protocols (OSPF, EIGRP) only. Distance Vector only uses FULL Networks only A,B,C Network 10.0.0.0 ( Class A Network)Command>Show IP route IGRP ProtocolI 10.1.5.0 [100/1047] via 10.1.4.252, 00:00:18, Serial 0Route to: Subnet 10.1.5.0 ---- Through --- Route VIA 10.1.4.252 on - Serial 0 Received Routing update on S0 at 00:00:18.CommandsShow IP Route Displays all Routes to other know Subnets.Show IP Protocols Show Routing Protocols Parameters and Current Timer Values.Show IP OSPF Interface List area which the interface, and Neighbors ADJACENT on this Interface.Debug IP OSPF EVENTS Issues LOG messages for each OSPF Packet.Debut IP OSPF Packet ISSUES Log Messages Describing the Contents of all OSPF Packets.Debug IP OSPF HELLO ISSUE LOG messages Describing Hellos and Hello Failures.OSPF uses RID (Route Identification) to identify routes.CommandShow IP OSPF Interface Displays this information You can set the Route ID with the following Command >Router-ID xxx Or >Show IP OSPF Neighbor----- Command will show it for all the Neighbors as well.Command to change the Hello sent time which automatically changes the Dead Interval Timer.Commands# INT FA0/0 Command #IP OSPF Hello 4 (Changes the Default of 10 to 4 seconds per HELLO)After the change the Dead Interval will change also to 4x4 = 16 4 = Hello sent time 4 seconds4 = Multiplied by default value16 = Dead Interval Timer = 16 SecondsDefault is 40 (Default Hello = 10 x 4 = 40seconds Dead Time Interval) 10 = Hello sent time 10 seconds4 = Multiplied by default value40 = Dead Interval Timer = 40 Seconds

Only EIGRP and OSPF use WILD Card with their network command:ClassLess ProtocolsCommand:>Router EIGRP 2>Network 192.1.2.3 0.0.0.255> Router OSPF 1> Network 192.1.2.3 0.0.0.0 area 0************Check and Make sure IGRP and RIP does not do it too.EIGRP All Routers using EIGRP must use the Same AS NUMBER. (Range 1- 65,353)EIGRP Show IP Protocols Shows Protocol Parameters and Current Timer Values.Show IP EIGRP Neighbors List EIGRP Neighbor (Also Called PEERS) Status.Show IP EIGRP TOPOLOGY- List the contents of the EIGRP TOPOLOGY including Successor and Feasible Successors. Show IP router EIGRP List only EIGRP Learned Routs form the Routing Table.Show IP Route EIGRP Traffic Lists Traffic Statistics about EIGRP.In the router Table for EIGRP the Successor Routes are Listed to see the Feasible Distance you will have to use the: Show IP EIGRP Topology ---------CommandEIGRP When EIGRP has Tow Equal Metric Routes to the same Subnet it places both to them in the Routing table and Load Balance packets across them (as Long as the Max paths are set to greater than (>1)) and Variance command is used To Show the Successor and Feasible Successor use the following Command: Show IP EIGRP Topology EIGRP Uses Feasible Distance (FD) from the >Show IP EIGRP Topology Listing command to tell the router the Feasible Distance to a route it is a Calculated Metric for the Route.Command:>Show IP EIGRP TOPOLOGYP 10.1.5.0/242 Successors, FD is 2681856 via 10.1.4.2 (2681856) Serial /0 Via 10.1.6.3(2681856) Serial /1Two Equal Cost Routes are listed There Metrics are the same.2681856 = is equal to the Metric for the Route. Since Both Routes have the same FD Metric both routes are considered Successor Routes for the route and Both Routes will be listed in the Routing Table Normally only 1 Successor Route is Listed.Command:>Show IP routeD 10.1.5.0 [90/2681856] via 10.1.4.2, 00:00:57, Serial 0 [90/2681856] via 10.1.6.3, 00:00:57, Serial 1 Both Routes listed are EIGRP Successor Routes.

The Packets needed to be sent to the subnet will be Load Balance between both of the Routes.The following Command:Router(config)#Bandwidth xxxTells the EIGRP the basis of the calculation for its Metric.

Command:#Show IP EIGRP TopologyP10.1.3.0 /24,1 Successor, FD is 2172416 Successor Routevia 10.1.6.3 (2172416/28160) Serial 0/1Feasible Successorvia 10.1.4.2 (2684416/1794560) Serial 0/0Feasible Distance = 2172416/1794560= ??????????? Calculated by Neighbor ???Command:#Show IP routeD10.1.3.0 [90/2172416] via 10.1.6.3 Serial 0/0Only Success Routes are Listed in the Show IP route Command??????When Trying to figure out the Network Command to use a more Specific Wild Card Mask:1) Use the following command to list the configured Interface:Command:# Show IP Interface Brief S010.1.2.32) Uses the Network Wild CardWild Card per ProtocolOSPF Network 10.1.2.30.0.0.0Area 0EIGRP- Network10.1.2.00.0.0.255

Route Summarization Reduces the size of the routing tables while maintaining routes to all the destinations in the Network also improves Convergence.Only used by Routing Protocols which Support VLSM:OSPFEIGRPCOMMAND#INT S0/0#IP Summary-Address EIGRP 1 10.3.0.0 255.255.0.0Variably Subnetted Means that more than one Subnet Mask is used in the Network (Route Summarized).Subnetted Means that there is NO Route Summery being Used in the Network.

Command used to see IP routes:#Show IP route10.0.0.0 /24is Subnetted, 11 Subnets (No Summarization is used)10.0.0.0 /8is Variably Subnetted 5 Subnets, 2 Masks/16/24*NULL 0 Interface Means that Packets matching this route are Discarded Command#Show IP routeD10.3.0.0. /16is a Summary 00:00:38 Null 0

VLSM- VARIABLE Length Subnet Mask Means, in a Single Class A,B,C Network, more than one subnet mask value is used :130.20.32.30130.20.32.36130.20.32.40 ???????????????

ClassFull Routing Protocols Do Not Transmit the Mask information along with the Subnet number when sending Packets:RIPIGRPClassLess Routing Protocols Do transmit the Mask Information when sending Packets: EIGRPOSPFRIP 2ISISClassFull Routing Protocols Accept a Static-Length Subnet Mask (SLSM) through the Network, because they can then reasonably assume that the Mask configured for the own Interface is the Same Mask Used through-out the Network.Auto-Summarization When a router has Interface in more than 1 Class A,B,C Network, It advertizes a single route for an entire Class A, B, or C Network in to the other Network. Only RIPIGRP(EIGRP-RIP-V2 the feature can be turned off)RIP and IGRP---Uses Auto-Summarization by Default and it Cannot be Turned OFF.Contiguous Network Is a single Class A,B,C Network for which all route to Subnets of the Network Pass through only other subnets of that same single Network.Discontinuous Networks Refers to the concept that, in a single Class A,B,or C netwkr, there is at least one case in which the only routs to one subnet pass through subnets of a different Network. ClassFull Routing Protocols Do not support a design with Discontinuous Networks.

ClassLess Routing Protocols Do support Discontinuous Networks.Basically if there are two routes in a Discontinuous Network and the Routing Process lists them in the routing table the router will load balance the packets and some packets will never get to the right equipment in the right network because the packets are sent to the wrong place.

To use Discontinuous Network ---- You will have to disable Autosummarization (only EIGRP and RIPv2 can be turned OFF) then all the routs will be listed in the Routing Table and the right route will be used.Discontinuous Network172.16.2.0 /24172.16.3.0 /24255.255.255.0255.255.255.010.2.1.0Serial 0/0Serial 0/110.3.4.010.2.2.0 (LANS)10.3.5.010.2.3.0Discontinuous Network10.3.6.0#Show IP RouteR 10.0.0.0 /8[120/1] via 172.16.3.3, 00:00:13 Serial 0/1Autosummarization[120/1] via 172.16.2.2, 00:00:13 Serial 0/0is on. This means that it will load balance the Packets and packets sent to the 10.0.0.0 will be Evenly sent to either side based on Traffic balancing instead of address, so some packets will be sent out the wrong interface and it will be dropped at the other side because the LANS are Not accessible from that Router. When you turn OFF Autosummarization (Only can be done with EIGRP and RIPV2) Then all Routes will be listed and used appropriately.#Show IP RouteD10.2.2.0 /24[90/2172416] via 172.16.2.2, 00:00:13Serial 0/1 D10.3.3.0 /24[90/2174213] via 172.16.3.3, 00:00:13Serial 0/1 This means it will Send the packets to the right Router Interface when Autosummarization is Disabled for EIGRP. Default Route Command#IP Route 0.0.0.0 0.0.0.0 168.13.1.101#IP Default Network 10.0.0.0 This command sets up the GateWay of Last Resort. If this command is not configured the Packet is Discarded if the Route to that Subnet is not listed in the Routing Table.*- Listed in the Routing Table means it is a Candidate to be the Default Route.EIGRP and IGRP Will always use the #IP Default Network 10.0.0.0OVER the #IP Route 0.0.0.0 0.0.0.0 168.13.1.101RIP will Always use the * (Default Route) Instead of using the IP Default Network command. #IP Route 0.0.0.0 0.0.0.0 168.13.1.101As the Default ClassFull (No IP ClassLess command) The default Route is only used when the route is not in the Routing Table and it does Not Match any Class A, B, C Network if it does and is not a Specific Match the Packet discarded. ClassLess (IP Classless Command) If the Packet Does Not Match it will Always use the Default Route.#IP ClassLess(ClassLess)#No IP ClassLess (ClassFull)

Packet Routing Flow With Routers

Incoming Packet

Check Routing Table

Is the Route a Connected Route ?

YES Route to that Interface Packet Sent to InterfaceNo

Router Check Routing TableRoute to an IP address VIA IP Address x.x.x.x used by Static Routes AND Routing Protocols

Then Forwards the Packets OUT that INTERFACE

If not use the Default Network/Route configuration based On ClassFull or ClassLess Routing Rules. Only Networks and SubNetworks are Located in the Router Table.#Show IP RouteClass A, B, CC X.X.X.X[Administrative Distance/ Metric] (NO VIA) Serial 0/0Used by :Connected RoutesSX.X.X.X[Administrative Distance/ Metric] VIA X.X.X.XVIA Used by :Static RoutesRIP RoutesIGRP RoutesOSPF RoutesEIGRP RoutesCIDR- ClassLess Interdomain Routing (RFC- 1817) Works by using a Routing Protocol that Exchanges the Mask as well as the Subnet/ Network number a ClassLess view of the Number can be attained.Without CIDR a customer would get 198.0.0.0 and entire Class C Network.With CIDR a customer would only get what the customer NEEDS, 25 IP addressA Customer would get25 IP address out of the 198.8.3.16 Range 198.83.17.30No IP address Space is wasted and a customer can use NAT to Provide Internet Access with PAT or something similar.

To use a secondary IP address on a Single Interface Use:Command:Router# Configure TerminalRouter (config)# Interface Serial 0/0Router(config-interface)- IP address 10.2.4.1 255.255.255.0Router (config-interface)- IP address 10.2.4.2 255.255.255.0 SECONDARY

Native VLAN does not need to be configured on an interface:Command:#Interface FastEthernet 0/0#IP address 10.1.1.1 255.255.255.0#Interface FastEthernet 0.2 (Virtual Interface)#IP Address 10.1.2.1 255.255.255.0 (Native Vlan Configuration) Data Encapsulation Not Needed for Native VLAN.#Interface Fastethernet 0.3#IP Address 10.1.3.1 255.255.255.0#encapsulation dot1q (Non-Native Vlan Configuration) Data Encapsulation(dot1q =802.1q = Protocol Data encapsulation)Or#encapsulation ISL(For Cisco Only equipment)

Routers use Multiple routes with equal metrics because they can be used as backup routes in case the route with the better metric fails. With multiple routes the convergence is almost instantaneous.To tell the router to use the best Route traffic-share min command and the Variance command to Round up the metric and this will be a good strategy for a quick convergence when a route fails. Administrative Distance is used to determine the best/ most Trusted route to a Subnetwork when there are multiple routing protocols pointing to the same subnet. The lower the administrative distance the more trusted that route is as a trusted quick route to another subnet.Administrative Distance per routing protocol:EIGRP 90IGRP100OSPF110ISIS115RIP 120Command# Show IP route R160.20.2.2[120/2] via serial 0/1[Administrative Distance/ Metric] (Metric is HOP count for RIP)When two routing protocol learn a route to another network the one with the lowest administrative distance will be put in the routers routing table. Link State Protocol Calculates the lowest Cost to a subnet when there are multiple routes to the same subnet Link State protocols chooses the route with the lowest metric (cost which is determined by the Bandwidth command on the interface) and puts that route in the routing table.

The Metric is calculated based on the topological Data which is received in large advertisements from other Link Ste Routers.Metric Calculation:Calculation = 10^8/64,000 (link Bandwidth) = 1562.510^8 = Standard format for calculation does not change10^8= 10000000064,000 = 64k which is equal to the bandwidth of the Circuit.Bandwidth Per Circuit TypeSerial Point-to-Point = 64k or 64,000bitsT1 connection= 1.544mb or 1544000Dialup connection= 56k or 56,0001556.5 = Link State Protocol Metric Calculation Value of the Cost to a Subnet.Standard Metric Cost for various common LinksSerial Point-to-Point = 64k or 64,000bits 10^8/64,000 (Link Bandwidth) = 1562.5T1 connection= 1.544mb or 154400010^8/1544000 (Link Bandwidth) = 64 (Cost metric)Dialup connection= 56k or 56,00010^8/56000 (link Bandwidth) = 1758.7 (Cost metric)

The Higher the Bandwidth the lower the Cost Metric and Visa Versa.

Distance Vector Protocols only send sparse information sent from other Distance Vector routers sending up dates:Rip sends updates every 30sechold-down timer is 180secIGRP sends updates every 90 sechold-down timer is 280 secRIP Version 2RIP Version 2 (RIPv-2), as currently defined in RFC 2453, defines several enhancements to the original RIP protocol. RIP- uses distance vector logic; uses hop count for the metric: sends full periodic updates; and still converges relatively slowly.RIP-V2 does add support for VLSM, as compared with RIP-V1, making it a classless routing protocol, with RIP-V2 including the subnet mask for each subnet in the routing updates.

Improvements Made to RIP by RIP-V2FeatureDescriptionTransmits subnet mask with routeThis feature allows VLSM by passing the mask along with each route so that the subnet is defined exactly. It allows VLSM, making RIP-V2 a classless routing protocol.Provides AuthenticationBoth clear text and MD5 encryption can be used to authenticate the source of routing update. Includes a next-hop Router IP address inIts routing updateA router can advertise a route but direct any listeners to a different router on the same subnet.Uses external routeTagsRIP can pass information about routes learned form and external source redistributed into RIP Another router then can pass these external tags to that same routing protocol in a different part of the network, effectively helping that other routing protocol pass information.

Uses multicasting Routing updatesInstead of broadcasting updates to 255.255.255.255 like RIP-1, the destination IP address is 224.0.0.9, an IP multicast address, 224.0.0.9 is reserved specifically for the use by RIP-V2. This reduces the amount of processing required on non-RIP speaking hosts on a common subnet.

The Route TableThe route table shows the best route possible to any know networks. The route table is used by the routers switching function to know which interface and next-hop destination to use fro forwarding any packets. A separate route table exists for each routable, or routed, protocol enabled on the router. As mentioned in the last section, IP routing is on by default but any other protocols, such as IPX or AppleTalk, need to be explicitly enabled.The command to enable IPX routing will be covered in the next chapter. The command to enable IP routing is ip routing, which is issued in the global configuration mode. Since it is on by default, we need to use it only if someone has issued a no ip routing command, which would turn the feature off.Router# ip routeThe Show ip Route CommandTo see the IP route table, use the Router# Show Ip route One of the commands we use to extensively to confirm connectivity is the Cisco ping command.Router#ping 192.168.5.1The exclamation marks (!) from the output/response indicate that we were successful on every effort.

By default SPLIT Horizon is on by default, Meaning Routers will not send routing information out interfaces which it learned the Route information from.

Static RoutesA static route is one that is explicitly configured and entered directly into the route table. Static routs always take precedence over router chosen by any dynamic routing protocol. Static routs are created in global configuration mode and have the following Command:Syntax: ip route network-address subnet-mask next-hop; Example, ip route 192.168.5.0 255.255.255.0 192.168.90.2 Lab-A# config tLab-A (config)# ip route 192.168.5.0 255.255.255.0 192.168.90.2Lab-A (config)#^ZRemember to use the ip address of the other router interface ip address when using static IP-Addressing.Default RoutesA default route is a route table entry that is used to forward frames for which no network entry explicitly list in the rout table. Loosely interoperated, if you dont find the network here, go to this address and that router will assist you. The syntax of the default route is IP route 0.0.0.0 0.0.0.00 next hop.For example Router# ip route 0.0.0.0 0.0.0.0 192.168.90.1Dynamic RoutingDynamic routing, once configured, adjusts automatically to network topology or traffic changes. This updating is accomplished by sharing route information with neighbor routers. The routing protocol determines thee frequency and method of updating the route information.For router to share information, they must be running the same routing protocol. Cisco router support many routing protocols, each of which is enabled in global configuration mode using the Router protocol-name command. To disable a routing protocol, type no router protocol-name, and any additional configuration will be removed.

Gateway of Last Resort Rules********IP Default-Gateway is only used when there is no IP routing used in the routerCommand:# No ip route#IP Default-Gateway 172.16.13.4 (used in boot mode)IP Default-Network --- Used when IP router is enabled.Command#IP routing#IP Default network 198.10.1.0IP Default-Network- uses ClassFull address Network Number:Command# IP address 198.10.1.0IP Default-Gateway must use the major network address# IP address 170.69.0.0 Major network address# IP address 170.69.24.0Routing Decisions are based on the following:****Static Routes ---------------------------------- IP route xxxx.xxxx.xxxx.xxxx Default Gateway --------------------------- IP default-GatewayDefault Network-----------------------------IP Default-NetworkDefault -IP route------------------------------IP Route (Rip only)Routing ProtocolsAdministrative DistanceRipv1, Ripv2120OSPF110IGRP100EIGRP90Rules used to chose the correct Route:Administrative Distance1) Connected Routes-----------------------------02) Static Routes------------------------------------ 13) Routing Protocols EIGRP90IGRP100OSPF110RIP1204) Default Routes- Are used when there are no matching Routes in the Routing Table.#Gateway of last for Resort xxxx.xxxx.xxxx.xxxx64k

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