Routing Protocols and Concepts: Ch9 - EIGRP

Suez Canal University – Faculty of Computers & Informatics - Cisco Local Academy

Routing Protocols and Concepts

CH9: EIGRP

Abdelkhalik [email protected]@gmail.com

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mailto:[email protected]


Introduction

• EIGRP is a Classless DV “not hybrid” routing protocol.• Cisco proprietary, Released in 1992 with IOS 9.21. • The main purpose was to create a classless version of IGRP.

IGRP:1985, overcome RIPv1’s metric and network size.Classful DV routing protocol uses Bellman-Ford algorithm.Both IGRP & EIGRP use composite metricDiscontinued support starting with IOS 12.2.

• EIGRP new features that are not found in other DV ProtocolsRTP Provides reliable & unreliable delivery of EIGRP packets.Bounded Updates.DUAL guarantees loop-free paths and backup paths.Establishing Adjacencies, Neighbor and Topology Tables.


IGRP to EIGRP

Enhanced Distance Vector Routing Protocol

Traditional Distance Vector Routing Protocols

1. DUAL algorithm2. Route entries doesn’t age

out, Uses Hello protocol to monitor connection status.

3. No periodic updates.

1. Bellman-Ford or Ford-Fulkerson algorithm.

2. Age out routing entries.3. Use periodic updates.

Algorithm

1. Topology table contains best path and loop-free backup path.

2. DUAL uses backup path in case of unavailable route.

1. Keep track of only the best routes.

2. The router must wait for a new routing update in case of unavailable route.

Path determination

Faster convergence Slower convergence due to hold-down timers.

Convergence


EIGRP Message Format


EIGRP Packet Header

• Opcode: specifies the EIGRP packet type: Update (1). Query (3). Reply (4). Hello (5).

• Autonomous System (AS): Number specifies the EIGRP routing process, also called “Global Process ID”. ID for EIGRP Routing process, Cisco routers can run multiple instances of EIGRP.


TLV: EIGRP Parameters

• The EIGRP parameters message includes the weights that EIGRP uses for its composite metric.

• K1 field for bandwidth and the K3 for delay are both set to 1.• The Hold Time is the maximum time router should wait for

the next hello.


TLV: IP Internal

• The IP Internal message is used to advertise EIGRP routes within an autonomous system.

• Delay: sum of delays from source to destination in units of 10 microseconds.

• Bandwidth is the lowest configured bandwidth of any interface along the route.


TLV: IP External

• The IP External message is used when external routes are imported into the EIGRP routing process.


Protocol Dependent Modules (PDM)

• EIGRP uses PDM to route several different protocols “IP, IPX & AppleTalk”.

• PDMs are responsible for the specific routing task for each network layer protocol.


Reliable Transport Protocol (RTP)

• RTP: is the protocol used by EIGRP for the delivery and reception of EIGRP packets.

• EIGRP was designed as a Network layer independent routing protocol.

• EIGRP replaces TCP with RTP.• Involves both reliable “ack” &

unreliable “no ack” delivery of EIGRP packets.

• RTP Packets can be sent either Unicast or Multicast “224.0.0.10”.


EIGRP Packet Types

• Hello packetsUsed to discover neighbors & form adjacencies with those

neighbors. Multicasts and use unreliable delivery.


EIGRP Packet Types

• Update packetsUsed to propagate routing information.Are Triggered, Partial, Bounded and not Periodic. Use reliable delivery.Multicast / Unicast.

• Acknowledgement packetsUsed to acknowledge

receipt of update, query & reply packets.

Use unreliable delivery. Always Unicast.


EIGRP Packet Types

• Query & Reply packetsQuery Packet: used by DUAL for searching for networks.Reply Packet: automatically sent in response to query.Both use reliable delivery.Query packets are either Unicast or Multicast.Reply packet are only Unicast.


Purpose of Hello Packet

• To discover & establish adjacencies with neighbor routers.• Time interval for sending hello packet

5 seconds: High bandwidth (greater than T1) 60 seconds: Low bandwidth, NBMA networks (T1 or slower ).

• Holdtime: the maximum time the router should wait to receive the next Hello before declaring that neighbor as unreachable.

• Holdtime = 3 times hello interval.


EIGRP Bounded Updates

• EIGRP uses the term partial or bounded when referring to its update packets.Partial: update only includes information about route

changes “not the full routing table”.Bounded only routers affected by the change will receive the

update .• The partial update is automatically "bounded“.• EIGRP minimizes the bandwidth required to send EIGRP

packets.

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DUAL: An Introduction

• DUAL: is the convergence algorithm used by EIGRP.• Provides for fast convergence time by keeping a list of loop-free

backup routes.• The decision process for all route computations is done by the

DUAL FSM.• FSM: is a model of behavior composed of a finite number of

states, transitions between those states, and events or actions that create the transitions.


Administrative Distance (AD)

• the trustworthiness “preference” of the source route.


Authentication

• EIGRP canEncrypt routing information.Authenticate routing information.

• Note: Authentication does not encrypt the router's routing table.


EIGRP Network Topology


Basic EIGRP configuration: AS & Process ID

• AS is a collection of networks under the control of a single authority that presents a common routing policy to the Internet. (RFC 1930). AS Numbers are assigned by IANA. Prior to 2007, AS numbers were 16-bit numbers. Now 32-bit AS numbers are assigned. Entities needing AS numbers: ISP


Basic EIGRP configuration: AS & Process ID

• EIGRP AS number actually functions as a Global process ID.• Process ID represents an instance of the routing protocol

running on a router.


The Router EIGRP Command

• router eigrp autonomous-system • All routers in the EIGRP routing domain must use the same

process ID number (AS Number)


The Network Command

• Functions of the network command1. Enables interfaces that belong to the advertised network to send &

receive EIGRP updates.2. Includes network or subnet in EIGRP updates.

• Router(config-router)#network classful_network_address.


The Network Command with a Wildcard Mask

• Wildcard mask is used when the network administrator does not want to include all interfaces within a network when enabling EIGRP.

• Think of a wildcard mask as the inverse of a subnet mask.255.255.255.255 -255.255.255.252-----------------------0. 0. 0. 3 “Wildcard mask”

• Router(config-router)#network network-address [wildcard-mask]


Verifying EIGRP

• EIGRP routers must establish adjacencies using Hello with their neighbors before any updates can be sent or received.

• To view neighbor table use: show ip eigrp neighbors

• Common Adjacency problems1.Different process ID.2.Incorrect network command.3.Passive-interface.


Verifying EIGRP

• The show ip protocols: used to verify that EIGRP is enabled.


EIGRP Metric Calculation

• EIGRP uses Bandwidth, delay, reliability, and load in its metric:

• Verifying the K Values


Examining the Metric values

• Bandwidth: The value of the bandwidth may or may not reflect the actual physical bandwidth of the interface. Most serial interfaces use a default bandwidth value of 1.544Mbps (T1)

• Delay: a measure of the time it takes for a packet to traverse a route.


Examining the Metric values

• Reliability: how often the link has experienced errors.Reliability is expressed as a fraction of 255. The higher the value, the more reliable the link.

• Load: reflects the amount of traffic utilizing the link.Load is expressed as a fraction of 255.A lower load value is more desirable because it indicates less

load on the link.


Using the Bandwidth Command

• The bandwidth command only modifies the bandwidth metric used by routing protocols not the physical metric.

• Verifying the bandwidth


Calculating the EIGRP metric


Calculating the EIGRP metric


DUAL Concepts

• Successor: The next hop in the best path.• Feasible distance (FD): Best Path metric.


DUAL Concepts

• Feasible successor (FS): The next hop in the backup path.• Reported distance (RD)/ AD :The distance (metric) from the

next hop to the destination network.• Feasibility Condition (FC): RD<FD.


DUAL Concepts


Topology Table: Successor and Feasible Successor



INFO ABOUT A SPECIFIC ENTRY IN THE TOPOLOGY TABLE



VIEW ALL POSSIBLE LINKS WHETHER THEY SATISFY THE FEASIBLE CONDITION OR NOT


DUAL Finite State Machine

• FSMs are used to describe how a device, computer program, or routing algorithm will react to a set of input events.


DUAL Finite State Machine


The Null0 Summary Route

• By default, EIGRP uses the Null0 interface to discard any packets that match the parent route but do not match any of the child routes

• EIGRP automatically includes a null0 summary route as a child route whenever both of the following conditions exist

1. There is at least one subnet that was learned via EIGRP.2. Automatic summarization is enabled.


Disabling Automatic Summarization






Manual Summarization


Manual Summarization


EIGRP Default Route


Fine-tuning EIGRP

• EIGRP Bandwidth UtilizationBy default, EIGRP will use only up to 50 percent of the

bandwidth of an interface for EIGRP information.

• Configuring Hello Intervals and Hold Times


Thank you..

Technology

Routing Protocols and Concepts: Ch9 - EIGRP