13. eigrp and ospf

Enhanced IGRP (EIGRP) and Open Shortest Path first (OSPF)

EIGRP

EIGRP is a classless routing protocol.It is a Cisco protocol.

AS number

It uses the concept of an autonomous system to describe the set of routers that run the same routing protocol and share routing information.

Hybrid routing protocol

EIGRP is sometimes referred to as a hybrid routing protocol. Because it has characteristics of both distance-vector and link-state protocol.

Hop counting

EIGRP has a maximum hop count of 255. (the default is set to 100)

EIGRP features

It supports for IPv4 and IPv6 .Considered classless (same as RIPV2 and

OSPF)Communication via reliable Transport

Protocol.Best path selection via Diffusing Update

Algorithm (DUAL)

Protocol-dependent modules

One of the most interesting features of EIGRP is that it provides routing support for multiple network protocols: IP, IPX, Apple Talk and now IPv6.

It is also known as PDM.

Neighbor Discovery

When EIGRP routers receive their neighbors updates, they store them in a local topology table.

This local topology contains all known routes from all known neighbors and serves as the raw material from which the best routes are selected and placed into the routing table.

EIGRP table

EIGRP maintains 3 types of table to maintain neighbor’s information –

1. topology table 2. neighbor table3. routing table

RTP

Reliable Transport ProtocolEIGRP uses a protocol called RTP.This protocol is used to manage the

communication of message between EIGRP- speaking routers.

DUAL

Diffusing update algorithmEIGRP uses DUAL for selecting and

maintaining the best path to each remote network.

Multiple ASes

EIGRP uses autonomous system numbers to identify the collection of routers that share route information.

Only routers that have same autonomous system numbers share routes.

Route Discovery and maintenance

The hybrid nature of EIGRP is fully revealed in its approach to route discovery and maintenance.


EIGRP uses a series of tables to store important information about its environment

1. Neighbor ship table2. Topology table3. Route table


Neighbor ship table

The neighbor ship table records information about routers with whom neighbor ship relationship have been formed.


Topology table -:

The topology table stores the route advertisements about every route in the internetwork received from each neighbor.


Route table -:

The route table stores the routes that are currently used to make routing decisions.

EIGRP metrics

There are 4 types of metrics –

1. Bandwidth2. Delay 3. Load 4. Reliability

Maximum paths and hop count

EIGRP can provide equal-cost load balancing of up to four links.

We can have EIGRP actually load-balance across up to six links by using the following command:

R1(config)# router eigrp 10R1(config-if)# maximum-paths ?<1-6> number of paths

Maximum paths and hop count

EIGRP has a maximum hop count of 100, but it can be setup to 255. # router eigrp 10 # metric maximum-hops ? <1-255> hop count

Configuring EIGRP

# config t# router eigrp 20# network 10.0.0.0# network 20.0.0.0# ctrl+z#copy run start

Passive-interface command

# router eigrp 20# passive-interface s 0/1/0 ctrl+z# copy run start

Verifying EIGRP

There are several commands that can be used on a router to help us troubleshoot and verify the EIGRP configuration. # show ip route # show ip route eigrp # show eigrp neighbors # show eigrp topology # show eigrp packet # debug ip eigrp notification

# show ip route eigrp

This command shows only EIGRP entries in the routing table.

# show ip eigrp neighbors This command shows all eigrp neighbors.

# show ip eigrp tolopogy

This command shows entries in the EIGRP topology table.

# debug eigrp packet

Shows hello packets sent/received between adjacent routers

# debug ip eigrp notification

This command shows EIGRP changes and updates as they occur on your network.

Successor path

Primary route to reach destination.

Routing table contains this successor path information.

Feasible successor

Backup route to reach the destination.

Topology table contains feasible successor path information.

DUAL FSM

DUAL finite state machine.

Working of DUAL FSM

1. FSM define a set of possible something can go through, what events causes those states and what event result from those states.

DUAL selects alternate routes quickly by using the information in the EIGRP table.

If a link goes down, DUAL looks for a feasible successor in its neighbor and topology table.

Hello packets

EIGRP uses small hello packets.Hello packets are sent every 5 seconds by

default.

RTP

Reliable transport protocol

RTP supports unicast and multicast.

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OSPF

Open shortest path firstIf you have multiple routers and not all of

them are Cisco, then we can not use EIGRP.

Dijkstra algorithm

OSPF works by using the dijkstra algorithm.

Wild card

# conf t# router ospf 1# network 192.168.0.0 0.0.0.15 area 0#network 193.168.0.0 0.0.0.3 area 0Ctrl+z# copy run start

OSPF Terminology

Link –

a link is network or router interface assigned to any given network.

router id -

the router ip is an IP address used to identify the router.

neighbor –

neighbor are two or more routers that have an inteface on a common network, such as 2 routers connected on a point-to-point serial link.

Adjency –

an adjency is a relationship between two OSPF routers that permits the direct exchange of route updates.

OSPF is really picky about sharing routing information - unlike EIGRP which directly shares routes with all of its neighbor.

OSPF directly shares routes only with neighbors that have also established adjencies.

Hello Protocol -

the OSPF Hello provides dynamic neighbor discovery and maintain neighbor relationships.

hello packets and link state advertiesment (LSA) build and maintain topological database

Neighborship database -

The Neighborship database is a list of all OSPF routers for which hello packets have been seen.

topological database -:

The topological database contains information from all of the link state advertisement packets that have been received for an area.

Link state advertiesment -:

a link state advertiesment (LSA) is an OSPF data packet containing link-state and routing information that's shared among OSPF routers.

OSPF area -:

an OSPF area is a grouping of networks and routers. all routers in the same area share a common area id.

a router can be a member of more than one area at a time.

all the routers within the same area have the same topology table.

SPF Tree calculation

within an area, each router calculates the best/shortest path to every network in that same area.

this calculation is based upon the information collected in the topology database and an algorithm

called shortest path first.

Enabling OSPF

There are two basic elements of OSPF configuration-

1. Enabling OSPF2. Configuring OSPF

Enabling OSPF

r1(config)# router ospf <1-65535>

<1-65535> identifies the OSPF process ID.

It’s a unique number on this router that groups a series of OSPF configuration commands under a specific running process.

Different OSPF routers do not have to use the same process ID.

OSPF configuration

# conf t(config)# router ospf 1 (1 is

process ID)(config)# network 10.0.0.0 0.255.255.255

area 1# copy run start

# show ip ospf database

# show ip ospf interface

# show ip ospf neighbor

# show ip protocols

# debug ip ospf packet

#debug ip ospf hello

#debug ip ospf adj

13. eigrp and ospf

Technology