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Anatomy of an IP PacketIP packets consist of the data from upper layers plus an IP header. The IP header consists of the following:
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Router
Router
Router
Router Router
What is an optimal route ?
What is an optimal route ?
Switch
Switch
Routing Protocol
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Path Determination Graphic
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Routing Protocols
Routing protocols includes the following:
processes for sharing route information allows routers to communicate with other routers to update and maintain the routing tables
Examples of routing protocols that support the IP routed protocol are:
RIP, IGRP, OSPF, BGP, and EIGRP.
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Routed ProtocolsProtocols used at the network layer that transfer data from one host to another across a router are called routed or routable protocols. The Internet Protocol (IP) and Novell's Internetwork Packet Exchange (IPX) are examples of routed protocols. Routers use routing protocols to exchange routing tables and share routing information. In other words, routing protocols enable routers to route routed protocols.
Dynamic Routing Protocols• Function(s) of Dynamic Routing Protocols:
–-Dynamically share information between routers.–-Automatically update routing table when topology changes.–-Determine best path to a destination.
Dynamic Routing Protocols• The purpose of a dynamic routing protocol is to:
–-Discover remote networks–-Maintaining up-to-date routing information–-Choosing the best path to destination networks–-Ability to find a new best path if the current path is no longer available
Dynamic Routing Protocols• Components of a routing protocol
–Algorithm• In the case of a routing protocol algorithms are used for
facilitating routing information and best path determination
–Routing protocol messages• These are messages for discovering neighbors and exchange of
routing information
Static RoutingStatic routing algorithms are basically table mappings established by the network administrator before the beginning of routing. These mappings do not change unless the network administrator alters them. Algorithms that use static routes are simple to design and work well in environments where network traffic is relatively predictable and where network design is relatively simple. Because of this fact, static routing systems cannot react to network changes.Static routes remain in the routing table even if the specified gateway becomes unavailable. If the specified gateway becomes unavailable, you need to remove the static route from the routing table manually. However, static routes are removed from the routing table if the specified interface goes down, and are reinstatedwhen the interface comes back up.
Static Routing• Advantages of static routing
–-It can backup multiple interfaces/networks on a router–-Easy to configure–-No extra resources are needed–-More secure
• Disadvantages of static routing–-Network changes require manual reconfiguration –-Does not scale well in large topologies
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Configuring Static RoutesStatic routes are table mappings established by the network administrator before the beginning of routing. These mappings do not change unless the network administrator alters them.
A static route uses this format:
route if_name dest_ip mask gateway_ip [distance]
Example:hostname(config)# route outside 10.10.10.0 255.255.255.0 192.168.1.1 [1]
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Configuring Default RoutesDefault routes are used to route packets with destinations that do not match any of the other routes in the routing table.
A default route is actually a special static route that uses this format:
ip route 0.0.0.0 0.0.0.0 [next-hop-address | outgoing interface]
This is sometimes referred to as a “Quad-Zero” route.
Example using next hop address:
Router(config)#ip route 0.0.0.0 0.0.0.0 172.16.4.1
Example using the exit interface:
Router(config)#ip route 0.0.0.0 0.0.0.0 s0/0
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Verifying StaticRoute Configuration
After static routes are configured it is important to verify that they are present in the routing table and that routing is working as expected.
The command show running-config is used to view the active configuration in RAM to verify that the static route was entered correctly.
The show ip route command is used to make sure that the static route is present in the routing table.
Classifying Routing Protocols• Dynamic routing protocols are grouped according to
characteristics. Examples include:
–-RIP–-IGRP–-EIGRP–-OSPF–-IS-IS–-BGP
• Autonomous System is a group of routers under the control of a single authority.
Classifying Routing Protocols• Types of routing protocols:
–-Interior Gateway Protocols (IGP)–-Exterior Gateway Protocols (EGP)
Classifying Routing Protocols• Interior Gateway Routing Protocols (IGP)
–-Used for routing inside an autonomous system & used to route within the individual networks themselves.–-Examples: RIP, EIGRP, OSPF
• Exterior Routing Protocols (EGP)–-Used for routing between autonomous systems–-Example: BGPv4
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Autonomous System
AS 2000
AS 3000
IGPInterior Gateway Protocols areused for routing decisionswithin an Autonomous System.
Exterior GatewayProtocols are usedfor routing betweenAutonomous Systems
EGP
AS 1000
An Autonomous System (AS) is a group of IP networks, which has a single and clearly defined external routing policy.
Fig. 48 IGP and EGP (TI1332EU02TI_0004 The Network Layer, 67)
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IGP
Interior Gateway Protocol(IGP)
Exterior Gateway Protocol (EGP)
EGP
EGP
EGP
Interior Gateway Protocol(IGP)
AS 1000
AS 2000
AS 3000
Fig. 49 The use of IGP and EGP protocols (TI1332EU02TI_0004 The Network Layer, 67)
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IGP and EGPAn autonomous system is a network or set of networks under common administrative control, such as the cisco.com domain.
Classifying Routing Protocols• IGP: Comparison of Distance Vector & Link State
Routing Protocols–Distance vector– routes are advertised as vectors– of distance & direction.– incomplete view of network– topology.–Generally, periodic– updates.–Link state– complete view of network – topology is created.– updates are not – periodic.–
Classifying Routing Protocols
Classifying Routing Protocols
• Classful routing protocols–Do NOT send subnet
mask in routing updates• Classless routing
protocols–Do send subnet mask
in –routing updates.
Classifying Routing Protocols• Convergence is defined as when all routers’
routing tables are at a state of consistency
Routing Protocols Metrics• Metric
–A value used by a routing protocol to determine which routes are better than others.
Routing Protocols Metrics• Metrics used in IP routing protocols
–-Bandwidth–-Cost–-Delay–-Hop count–-Load–-Reliability
Routing Protocols Metrics• The Metric Field in the
Routing Table• Metric used for each
routing protocol–-RIP - hop count–-IGRP & EIGRP - Bandwidth (used by default), Delay (used by default), Load, Reliability–-IS-IS & OSPF – Cost, Bandwidth (Cisco’s implementation)
Routing Protocols Metrics• Load balancing
–This is the ability of a router to distribute packets among multiple same cost paths
Administrative Distance of a Route• Purpose of a metric
–It’s a calculated value used to determine the best path to a destination
• Purpose of Administrative Distance–It’s a numeric value that specifies the preference of a particular route
Administrative Distance of a Route• Identifying the Administrative Distance (AD)
in a routing table–It is the first number in the brackets in the routing table
Administrative Distance of a Route• Dynamic Routing Protocols
Administrative Distance of a Route• Directly connected routes
–Have a default AD of 0• Static Routes
–Administrative distance of a static route has a default value of 1
Administrative Distance of a Route• Directly connected routes
–-Immediately appear in the routing table as soon as the interface is configured
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Categories of Routing Protocols
Most routing algorithms can be classified into one of two categories:
• distance vector • link-state
The distance vector routing approach determines the direction (vector) and distance to any link in the internetwork.
The link-state approach, also called shortest path first, recreates the exact topology of the entire internetwork.
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Distance VectorRouting Concepts
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2 Hops
1 Hop1 Hop
Destination
192.16.1.0
192.16.5.0
192.16.7.0
Distance
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Routing table contains the addressesof destinations and the distanceof the way to this destination.
Flow of routinginformationFlow of routinginformation
Router B Router CRouter A Router D
192.16.1.0192.16.1.0 192.16.7.0192.16.7.0
192.16.5.0192.16.5.0
Distance Vector Routing (DVR)
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Routing Tables Graphic
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Distance VectorTopology Changes
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Router Metric Components
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Router CRouter A Router D
192.16.1.0192.16.1.0 192.16.7.0192.16.7.0
192.16.5.0192.16.5.0
Router B
192.16.3.0192.16.3.0
192.16.2.0192.16.2.0
192.16.4.0192.16.4.0
192.16.6.0192.16.6.0
192.16.1.0192.16.1.0
192.16.2.0192.16.2.0
192.16.4.0192.16.4.0
192.16.5.0192.16.5.0
192.16.6.0192.16.6.0
192.16.6.0192.16.6.0
192.16.7.0192.16.7.0
192.16.2.0192.16.2.0
192.16.3.0192.16.3.0
192.16.4.0192.16.4.0
192.16.4.0192.16.4.0
192.16.5.0192.16.5.0
192.16.6.0192.16.6.0
192.16.6.0192.16.6.0
192.16.7.0192.16.7.0
192.16.1.0192.16.1.0
192.16.2.0192.16.2.0
192.16.2.0192.16.2.0
192.16.3.0192.16.3.0
192.16.4.0192.16.4.0192.16.3.0192.16.3.0
192.16.4.0192.16.4.0 192.16.1.0192.16.1.0
192.16.5.0192.16.5.0
192.16.6.0192.16.6.0
192.16.3.0192.16.3.0
192.16.2.0192.16.2.0
192.16.7.0192.16.7.0
192.16.5.0192.16.5.0
192.16.4.0192.16.4.0
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LL Locally connectedLocally connected
Distance Vector Routing (DVR)
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192.16.4.0192.16.4.0
192.16.5.0192.16.5.0
192.16.6.0192.16.6.0
192.16.6.0192.16.6.0
192.16.7.0192.16.7.0
192.16.1.0192.16.1.0
192.16.2.0192.16.2.0
192.16.2.0192.16.2.0
192.16.3.0192.16.3.0
192.16.4.0192.16.4.0192.16.3.0192.16.3.0
192.16.4.0192.16.4.0 192.16.1.0192.16.1.0
192.16.5.0192.16.5.0
192.16.6.0192.16.6.0
192.16.3.0192.16.3.0
192.16.2.0192.16.2.0
192.16.7.0192.16.7.0
192.16.5.0192.16.5.0
192.16.4.0192.16.4.0
192.16.5.0192.16.5.0
192.16.6.0192.16.6.0
192.16.7.0192.16.7.0 192.16.1.0192.16.1.0
192.16.3.0192.16.3.0
192.16.2.0192.16.2.0
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192.16.4.0192.16.4.0
192.16.5.0192.16.5.0
192.16.6.0192.16.6.0
192.16.6.0192.16.6.0
192.16.7.0192.16.7.0
192.16.1.0192.16.1.0
192.16.2.0192.16.2.0
192.16.2.0192.16.2.0
192.16.3.0192.16.3.0
192.16.4.0192.16.4.0192.16.3.0192.16.3.0
192.16.4.0192.16.4.0 192.16.1.0192.16.1.0
192.16.5.0192.16.5.0
192.16.6.0192.16.6.0
192.16.3.0192.16.3.0
192.16.2.0192.16.2.0
192.16.7.0192.16.7.0
192.16.5.0192.16.5.0
192.16.4.0192.16.4.0
192.16.5.0192.16.5.0
192.16.6.0192.16.6.0
192.16.7.0192.16.7.0 192.16.1.0192.16.1.0
192.16.3.0192.16.3.0
192.16.2.0192.16.2.0
192.16.1.0192.16.1.0192.16.7.0192.16.7.0
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Distance Vector Routing (DVR)
Fig. 53 Distribution of routing information with distance vector routing protocol (cont.) (TI1332EU02TI_0004 The Network Layer, 71)
Link State Routing protocol
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Link State Concepts
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Link State Topology Changes
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LSP:„My links toR2 and R4 are up“
LSP: „My links toR1 and R3 are up,my link to R4 is down.“
LSP: „My links toR2 and R4 are up.“
LSP:„My links to R1 and R3 are up.
My link to R2 is down.“
Router 1 Router 4
Router 2 Router 3
SPF
RoutingTable
Link State Routing (LSR)
LSP....link state packetSPF... shortest path first
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Link State Concerns
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Router A Router C
Router B Router D
Router E22
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B - 2C - 1B - 2C - 1
A - 2D - 4A - 2D - 4
A - 1D - 2E - 4
A - 1D - 2E - 4
C - 2B - 4E - 1
C - 2B - 4E - 1
C - 4D - 1C - 4D - 1
Router A Router B Router C Router D Router E
Link State Database
AA
CB
D
E
A D
EC
BB
D A
E B
CC
E C B
A
DD
Link State Routing (LSR)
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Link State Routing FeaturesLink-state algorithms are also known as Dijkstras algorithm or as SPF (shortest path first) algorithms.
Link-state routing algorithms maintain a complex database of topology information.
The distance vector algorithm are also known as Bellman-Ford algorithms. They have nonspecific information about distant networks and no knowledge of distant routers.
A link-state routing algorithm maintains full knowledge of distant routers and how they interconnect. Link-state routing uses:
• Link-state advertisements (LSAs)A link-state advertisement (LSA) is a small packet of routing information that is sent between routers.
• Topological databaseA topological database is a collection of information gathered from LSAs.
• SPF algorithmThe shortest path first (SPF) algorithm is a calculation performed on the database resulting in the SPF tree.
• Routing tables – A list of the known paths and interfaces.
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Link State Routing
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Comparing Routing Methods
Questions
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