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EIGRP Protocol Tutorial & Configuration

· EIGRP stands for Enhanced Interior Gateway Routing Protocol.

· It Is A Cisco-Proprietary Routing Protocol For TCP/IP

· It Is Based On IGRP Routing Protocol

Features And Characteristics Of EIGRP

· It Is A Cisco Proprietary Routing Protocol

· It Is Based On IGRP Routing Protocol

· It Is An Enhanced Version Of IGRP Protocol

· In Comparison Of IGRP It Provides Faster Convergence Times, Superior Handling Of Routing Loops And Improved Scalability

· It Was Released In 1994

· It Is A Hybrid Routing Protocol

· It Has Characteristics Of Both Distance Vector And Link State Protocols

· It Uses DUAL[Diffusing Update Algorithm] Algorithm To Select The Best Path

· It Uses RTP[ Reliable Transport Protocol] To Communicate With Neighbours

· It Uses Multicast For Routing Updates

· EIGRP uses multicast packets to reduce bandwidth consumed on a link(One packets to reach multiple devices). All nodes on a network segment process broadcast packets, whereas with multicast, only nodes listening for the particular multicast group process the multicast packets.

· It Supports IP, Apple Talk And IPX Routed Protocols

· It Includes Subnet Mask Information In Routing Updates

· It Supports Route Summarization And Discontiguous Networks

· It Supports VLSM/CIDR

· It Supports Load Balancing Across The Six Routes For A Single Destination

· It Supports Trigger Updates

· Its Internal AD Value is 90 And External AD value Is 170, protocol Number is 88

· Distance vector Routing protocols use hop count as the metric for routing decisions, But EIGRP adds logic to the route-selection algoritm that uses factors besides hop count.

· Efficient Neigbhor discovery

· EIGRP Supports different Network Layer Protocols through the use of protocol-dependent module [PDMs]

· Each EIGRP PDM will maintains a separate series of tables containing the routing information. Means, There would be IP/EIGRP Table, IPv6/EIGRP table

· It Is Cisco Proprietary Protocol.

· It Is A hybrid Routing Protocol

· It has advantage of both link state and distance vector protocol

· It uses metric calculation formula to select the best route for destination

· It sends partial and full update only when something is change in network

· It maintain three tables for fast convergence

1. Neighbour table

2. Topology table

3. Routing table

Neighbour Table:

1. EIGRP share routing information only with neighbours

2. To know who the neighbours are, it uses neighbour table

3. When new neighbour is discovered, EIGRP would add its address and interface on which neighbour is connected in neighbour table

4. EIGRP uses separate neighbour table for each routed protocol

Topology table

• EIGRP uses this table to store all routes which it learned from neighbours

• It contains a list of all destination and routes advertised by neighboring routers

• EIGRP selects single best route for each destination from this table

• Other Routes are marked as backup routes

• EIGRP refers selected route as Successor and backup route as feasible Successor

• Show ip eigrp topology – It show successor and feasible successor link

• Show ip eigrp topology all-links – it show all links

Routing Table:

• EIGRP Stores single best Route for each destination

• Router uses this table to forward the packet

• Metric

• EIGRP uses metric to select the best route from all available routes fro destination.

Neighbor Discovery

· Before Exchange routes with each other, they must become neighbours.

· There are three conditions that must be met for neighborship establishment

1. Hello or ACK Received

2. AS Numbers Match

3. Identical Metrices [K Values]

· Link State Protocols tend to use Hello Messages To Establish Neighborship(Also Called Adjancies)

· To maintain the neighborship relationship, EIGRP routers must also continue receiving Hellos from their neighbours

· EIGRP Routers that belong to different Autonomous System Don’t Automatically share routing information and they don’t become neighbours

· EIGRP Advertise its entire routing table when it discovers a new neighbour and forms an adjancency with it through the exchange of Hello Packets

Autonomous Systems

· A router can run multiple EIGRP processes

· It is used to identify the group of routers that will share route information

· Each process operates under the context of an autonomous system

· Router use the same metric calculation formula and exchange routes only with members of the same autonomous system

There Are Four Terms of DUAL Algorithm

FD – [Feasible Distance]

RP – [Reported Distance of Advertised Distance]

Successor [Best Path]

Feasible Successor [Backup Path]

Successor:

· The Best Path To The Destination Is Called The Successor

· The Successor will be copied from the topology table to the routing table

· Successor is stored in topology table as well as in the routing table

Feasible Successor:

· It is a backup path of successor which is stored in topology table

· Successor is stored in topology table as well as in the routing table

Feasible Successor:

· It is a backup path of successor which is stored in topology table

Types of Messages/Packets In EIGRP

1. Hello

· It is used to establish & maintain neighbour relationship between the router

· Keep Alive

· Hello Timer = 5 Sec

· Hold Down Timer = 15 Sec

· Hello Packets are sent Through Multicast Address = 224.0.0.10

· Hello Packets Can be Multicast & Unicast

· It contain an acknowledgment number of 0

· EIGRP routers must form neighbor relationships before exchanging EIGRP updates

2. Update [ RTP]

· It is used to store prefix information/network information of routing table

· Update message can be unicast or multicast

· Use RTP Protocol

· It is sent between the neighbours to build the topology table and routing table

· If there is static neighbour-ship between the router than update message will be sent unicast

· Contain [subnets/Prefix, bandwidth, load, Delay, Reliability, MTU & hop Count]

· Used to communicate the routes that a particular router has used to converge

· EIGRP Updates are sent as multicasts when a new route is discovered or when convergence is completed.

· They are sent reliably between EIGRP routers.

3. Query [RTP]

· Query messages are sent by a router when successor route goes fail and there is no feasible successor in the topology table

· The routers place the route in active state and sent a query to its neighbours for an alternate route

· Query messages are sent as a multicast 224.0.0.10

4. Reply [RTP]

· It is sent in response to query message, packets to update alternate route

· Reply Packets are unicast

5. Acknowledgement

· It is sent as a unicast

· Ack is not used in the case of hello

· It is Just for RTP packets

· Used to acknowledge EIGRP Updates, Queries, and Replies

Metric Has Five Components:

1. Bandwidth

2. Load

3. Delay

4. Reliability

5. MTU

Note: Only bandwidth and delay are by default enabled

EIGRP Uses K value For Metric

K1 X 1 = Bandwidth

K2 X 0 = Load

K3 X 1 = delay

K4 X 0 = Reliability

K5 X 0 = MTU

Default K Value: Metric= K1 + K3

RTP

· EIGRP Uses RTP to communicate with other EIGRP Speaking routers

· RTP Uses multicast and unicast to exchange the data with neighbours

· It uses Class D address 224.0.0.10 for multicast

· EIGRP maintains a list of the neighbours who have replied

· It it doesn’t receive a reply from neighbours, RTP resend same data using unicast

· It sends 16 unicast attempts before declaring neighbor is dead

· EIGRP uses Reliable Transport Protocol (RTP) to ensure that packets are delivered in order and to ensure that routers receive specific packets.

· A sequence number is included in each EIGRP packet

· The sequence value zero does not require a response from the receiving EIGRP router

· Ensuring that packets are received makes the transport method reliable

· All update, query, and reply packets are deemed reliable, and hello and ACK packets do not require acknowledgment and could be unreliable

· Do Not Confuse With Real Time Transport Protocol[RTP] which is used to carry audio/video file over An IP Network

DUAL

· Diffusing Update Algorithm

· EIGRP Uses DUAL To provide the fastest route convergence among all protocols.

Route Convergence

· Selecting best route from all available routes

· Supporting VLSMs

· Dynamically recovering from route failure

· Finding an alternative route if primary route goes down

Autonomous System

· EIGRP Shares routing information only with neighbours

· In order to become a neighbour AS number must be matched

· AS create a logical boundary for route information

· By default router will not propagate route information outside the AS

Some useful command

#router eigrp 10

Maximum-paths

#router eigrp 10

Metric maximum-hops

#Show ip route

#Show ip route eigrp

#Show ip eigrp neighbours

#Show ip eigrp topology

#Debug eigrp packet

#Debug ip eigrp notification