EIGRP summary notes : CCNA/CCNP/CCIE

EIGRP  :

It’s a hybrid protocol .

AS number has to match in all EIGRP router

EIGRP does not support VLSM by default , to support VLSM must use no auto-summary command

split horizon always on ,

EIGRP uses own protocol 88  and DUAL algorithm

EIGRP uses multicast address 224.0.0.10

EIGRP manual summary address command  on interface  creates a null 0 route on local router routing table , and it gives administrative distance of 5 to  summary route .

EIGRP uses administrative distance 90 for normal routes  and 170 for external routes 

EIGRP will load balance across 4 equal cost path .by default unequal load balancing is off to enable unequal load balance use variance command  with value .

EIGRP routers use query message to find backup route around the network ,

a router send query message to its neighbor for its connected network , even if it is goes down , which is unrealistic , because it is sending a query for its own network to a neighbor .

EIGRP  (SIA ) stuck in active comes into play when a router wait to hear for a query , which is for 3 minute . and neighbor get re-initiated .

EIGRP stub ,  stub router does not receive a query message from neighbor.  Stub command  mostly used in hub-and-spoke network.

when EIGRP stub command  applied in a router by default it will advertise summary and connected routes to its neighbor .

EIGRP  stub receive-only  command ,,,,,, only  receives routes from neighbor   does not send anything to its neighbor .

when a router goes down in EIGRP send a final hello message which is called good bye message ..

if we use neighbor command update are send through unicast , both neighbor have

to have neighbor command in place

if you use passive interface command  , router will not exchange hellos , hence no neighbor relationship .

if u use split horizon on hub , to get the router from spoke to spoke

use neighbor command on all router .

EIGRP maintains a topology table , if a route goes down other route comes back from topology table

EIGRP does unequal cost load balancing

EIGRP router maintains 3 table   : neighbor table ,   topology table , routing table ,

EIGRP table and terminology :

Feasible Distance  (FD) : how far a route is from  me (router)

Advertise Distance (AD) : how far a route is from my neighbor router

Successor : which goes to routing table meaning a primary path

Feasible Successor : backup route  

Rule      :   to be consider a feasible successor the advertise distance must be less

than feasible distance of the successor . its a loop prevention mechanism

eigrp active   : meaning bad route,   router is trying to find an active route by sending query

eigrp passive :  good route , everything ok

EIGRP  uses 5 packet type for peering neighbor and route exchange:

hello   : forms relationship

update : sends update to each other

query : asks  about routes

reply : response to a query

ack  : acknowledges the update, query , and reply messages .

EIGRP  metric calculation :

  by default metric based on bandwidth and delay

Bandwidth  : can be configured manually on interface

Delay     :  can be configured manually on interface

reliability :

loading :

MTU :

ip default network ---- command   flag a default route to its neighbor