EIGRP

Advanced distance vector protocol

Partial Updates

VLSM Support

Data-Link Protocol Support

Fast Convergence

32 or 64-bit metric

IPv4 and IPv6

Runs above the IP Layer as protocol 88

Reliable Transport Protocol

Supports multicast (default) and unicast

Multicast address 224.0.0.10 or FF02::A

DUAL algorithm

IP EIGRP Neighbour Table

Neighbour IP Address

Local router exit interface to neighbor

List of directly connected adjacent EIGRP neighbor routers

IP EIGRP Topology Table

Destination

FD - Feasible Distance, end to end metric of the successor route

RD - Reported distance, metric from the perspective of the neighbouring router

List of all routes learned from each EIGRP neigbour or redistribution, and identifies successor routes and feasible successor routes.

Feasibility condition means the reported distance must be less than feasible distance to maintain loop-free topology.

IP Routing Table

Destination

Best Route

EIGRP Metrics

Composite metric based on bandwidth and delay, can also use reliability and load.

MTU not used for metic calculation

reliability and load issues cause retransmissions which increases delay.

Default values,

K1	1	Bandwidth
K2	0	Reliability
K3	1	Delay
K4	0	Load
K5	0	MTU
K6 (if available)	0	64-bit metrics, throughput and latency by default

Metric = ((K1 * bandwidth + (k2 * bandwidth) / (256 - load)) + K3 * delay) * K5 / (K4 + reliability)) * 256

With default K values,

Metric = (bandwidth + delay) * 256

Bandwidth =

10^7

/ minimum bandwidth along the path in kbps

Delay = sum of all delays in the path in tens of microseconds

Lowest metric is best. to influence metric adjust the delay on interface.


show ip eigrp topology 10.1.2.0 255.255.255.0

EIGRP Queries

Queries are sent when a route is lost and no feasible successor is available.

Queries sent to all neighbouring routers except on the interface of the successor

If neighbors have the lost route they answer the query and stop the query from spreading, if not the query is sent to their neighbours

Router must receive replies to all queries before a new path is calculated

If reply is lost or missing,

Route goes into stuck in active (SIA) state

Neighbour status is verified halfway through the active timer expiration, if no response, neighbour relationship is reset

EIGRP Stub Routers

Improves network stability

Reduces resource utilization

Simplifies remote router configuration

Used on access devices / remote sites

EIGRP Summary Routes

Summarization limits query scope and improves convergence

If router receives a query for a prefix described by a summary route, it immediately responds with a reply message,

Default Route

Can be statically defined using ip route and ipv6 route

EIGRP can redistribute static route using redistribute static command