Can Someone clarify EIGRP in the simplest form?

lAwBoY

I got a hard time trying to understand.

thanks

triple J

EIGRP is Enhanced Interior Gateway Routing Protocol. It is very similar but more advanced than IGRP.

It's a Cisco propriertary protocol. It is setup using rouer eigrp (as number).

It can interoperate with IGRP as long as the as number are the same.

It is a hybrid routing protocol meaning it uses some distance vector concepts and some link-state concepts.

It supports CIDR and VLSM so you can build a large scalable network.

Compared to OSPF or IS-IS (other scalable VLSM routing protocols) it is much easier to configure.

darkuser

http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/fipr_c/ipcprt2/1cfeigrp.htm

QUIX0TIC

Simplest form??? It is a mix of IGRP with OSPF. It takes the best parts of both while being a proprietary Cisco protocol.

2lazybutsmart

Well I've made my self a small summary of the points I thought were important in EIGRP. You need to understand the concepts in the right order. Make sure you get the 'terms' dialed in.

I know it's not small as I mentioned...but the summarization certainly helped me understand things better.


Overview
-EIGRP is a Cisco-proprietary classless, enhanced distance-vector routing protocol.
-Supports VLSM, CIDR, summarization, and discontiguous networks.
-EIGRP supports IP, IPX, and AppleTalk via separate PDMs (Protocol dependent modules) for each protocol.

Neighborhood Discovery
-Routers become neighbors when three conditions are met: 1- Hello or ACK received, 2- AS numbers match, 3- Identical metrics.
-EIGRP only advertises its entire routing table when it discovers a new neighbor and forms an adjacency. After that, only changes to the routing table are propagated from there on.

Important Terminology:
-Feasible distance: the best metric along all paths to a remote network. The metric of a feasible distance is the metric reported by the neighbor (reported distance) plus the metric to the neighbor reporting the route.
-Reported distance: the metric of a remote network as reported by the neighbor.
-Neighbor table: stores information about the neighbors (IP address and interface). There is one neighbor table per PDM. The table is stored in RAM.
-Topology table: stores information about all routes advertised by the neighbors. Each destination is recorded along with the neighbors who have advertised that destination. The table is populated by the PDMs. The table is stored in RAM.
-Feasible successor: is a backup route that is stored in the topology table.
-Successor: is the best route to a remote network. A successor route is used by EIGRP to route all traffic to a destination and is stored in the routing table.
Reliable Transport Protocol (RTP):
-RTP manages communication of messages between EIGRP-speaking routers.
-EIGRP uses the Class D address of 224.0.0.10 to send multicasts. It maintains a list of all neighbors who reply to its multicasts.
-If a neighbor doesn’t reply, it will switch to unicasts. If it doesn’t get a reply after 16 tries it will declare the neighbor dead.
-RTP uses sequence numbers to manage messages.
Diffusing Update Algorithm (DUAL):
-DUAL is responsible for selecting and maintaining information about the best paths to a remote network.

Multiple ASes
-EIGRP supports the use of multiple ASes on a single router.
-Route information is shared between ASes via redistribution.
-Route information that originates within a specific AS is called internal EIGRP routes.
-Route information that originates outside an AS are called external EIGRP routes and have an AD of 170. It doesn’t matter if they are originated by EIGRP or another routing protocol.

Discontiguous Networks and Summarization
-A discontiguous network is a network that has two or more subnetworks of a classful network connected together by a different classful network.
-EIGRP and RIPv2 support discontiguous networks, but not by default because they auto summarize at classful boundaries.
-OSPF supports discontiguous networks by default because it does not auto summarize at classful boundaries.
-EIGRP also supports the manual creation of summaries at classful boundaries.
-To configure discontiguous networks, use the no auto-summary command.

Route Discovery and Maintenance
-EIGRP works like a link-state protocol by the use of hello messages to discover and maintain the state of neighbors.
-EIGRP works like a distance-vector protocol by the use of the routing-by-rumor mechanism.
-EIGRP uses three tables to store routing information:
-Neighbor table: records information about neighbor routers
-Topology table: records information about routes advertised by neighbor routers.
-Route table: stores routes that are currently used to make routing decisions.

EIGRP Metrics
-EIGRP uses four metrics. Bandwidth, delay, load, and reliability. Bandwidth and delay are used by default.
-EIGRP can load-balance four unequal-cost links by default. It can do up to six by using the following command:
-Router(config)# router eigrp 10
-Router(config-router)# maximum-paths 6
-EIGRP has a maximum hop count of 100 by default. It can be increased to 255 by using the following command:
-Router(config)# router eigrp 10
-Router(config-router)# metric maximum-hops 255
-EIGRP uses the maximum hop-count to limit the scope of an AS.

Configuring EIGRP
-EIRP is configured using classful network addresses just like IGRP.
-To stop EIGRP from working on a specific interface, use the passive-interface command as follows:
-Router(config)# router eigrp 10
-Router(config-router)# passive-interface serial 0/1

2lbs.

Webmaster

Good list 2lbs!

Here's something I wrote for the BSCI exam, so it goes a bit further than you need to know for the CCNA, but should be useful for CCNA too:
www.techexams.net/technotes/bsci/eigrp.shtml

viper75

Nice list!!!