EIGRP Updates Breakdown

So, in order for the global routing table to have EIGRP routes in it, EIGRP has to first be enabled, then go through a process through with it determines which routes are Feasible successors (Best routes) and only then install them to the global routing table.

EIGRP has five basic messages it uses for this EIGRP collaboration between its neighbors.

  • Hello
  • Update
  • Query
  • Reply
  • ACK

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EIGRP Router ID is an important component to EIGRP and is a way for EIGRP to identify each router that is participating in the EIGRP ASN domain.

The EIGRP enabled router uses the following 3 steps to determine its ID:

  1. Manual configuration within the EIGRP config
  2. Highest IPv4 address on an enabled and operating loopback interface
  3. Highest IPv4 address on an enabled and operating non loopback interface

Manually configuring an EIGRP Router ID:

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EIGRP Basics (Static EIGRP Neighbors)

With basic EIGRP configurations there shouldn’t be any issues with EIGRP configured routers to able to create neighborships between each other. At this point I’m not 100% sure why this is an option but it is.

Below is an example of how to configure it. (I created a new sub-interface Gi0/0.70 on R1 and Fa0/1.70 on R3 for this example, just to not mess with the the current setup I have on sub-interface 60).

*** Super important, the static neighbor configuration needs to be configured on both routers ***

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EIGRP Basics (Passive Interfaces)

When EIGRP is up and operational, unicast and multicast EIGRP packets or constantly flooding the network to make sure EIGRP routes are up and are using the best path. These packets are important but not always necessary. There are situations when disabling an interfaces ability to spam the network with EIGRP packets is appropriate and will still allow for a fully operational EIGRP convergence. The way to achieve this is by configuring an interface to passive mode. EIGRP will still advertise the network/subnet configured on that interface, however, the interface will not participate in sending or processing of EIGPR packets.

Here is an example:

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EIGRP Basics (Manipulating EIGRP Hello and Hold Timers)

EIGRP works perfectly fine with its stock settings. However, there comes a time when settings need to get tweaked for various reason. EIGRP by default sends Hello packets every 5 seconds and has a Hold timer of 15 seconds. This means, by default, a router will send a hello packet every 5 seconds, and wait 15 seconds to receive a hello packet from its neighbors before it drops that route.

Hello packet set by each neighbor every 5 seconds:

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