EIGRP - QUICK NOTES

EIGRP                                                                                                         

•         IGP

•         Classless

•         Hybrid (Best of LS & Best of DV)   LS -> Convergence ,DV -> Simplicity in Config

•         Metric -> Composite Metric .By default it depends upon Bandwidth & Delay . But load , relability and MTU can be considered if the metric weights i.e K values are set to 1.   

•         Bandwidth in 10^7/ Bandwidth (kbps) and delay in 10microseconds.

•         Bandwidth =the lowest of the link along the path , Delay= sum of the all delays along the path

•         K Values = Metric Weight.

             K1 = Bandwidth =1 , K2= Load= 0 , K3= Delay =1 , K4/K5 = Reliability , MTU =0 (Container)

•         Load Balancing over unequal path is proportionate. This achieve due by Variance command.

By default EIGRP can do load balancing over 4 equal cost paths.

But we can load balancing up to 16 equal / unequal cost paths.

R1(config-router)# variance 2    ------multipler - best path cost will get multipled by 2 and which path whose cost  comes under that value over those path load balancing can happen.

•         EIGRP Neighbor relationship Rule:-

                1)They should be directly connected

                2) They should belong to same AS

                3) There K Values should be same.

•         EIGRP Summarization Rule:-

                1) Automatic Summarization will happen at Classful boundary.

                2) Manual Summarization will happen at at any arbitary boundary.

When summarization is configured on an interface , the router immediatley creates a route pointing to NULL 0. This is EIGRP LOOP Pervention Mechanism.

•         EIGRP control Packets:-     HQURA

                 1) Hello :- Establish neighbor relationship = Multicast

                 2) Query :- Ask neighbor about routing information = Normally multicast . Unicast (retransmitted)

                 3) Update :- Sending routing update = Unicast / Multicast

                 4) Reply:- Respond to query about routing information = Unicast

                 5) Ack :- Ack a reliable packet   = Unicast Hello packets .Ack - U Q R

•         EIGRP Timers

                Fast Neighbor ( bandwidth= > T1 1.544Mbps)  = 5 Secs and 15 Secs

                Slow Neighbor = 60 Secs and 180 Secs.

•         EIGRP AD Values

                 Summary routes = 5 , Internal routes = 90 , External routes =170.

•         Specality :- It elects next best path when it elects next best path.

                 Best path - Successor & Next Best path - Feasiable Successor

•         AD value (Advertised Distance) = Cost between Next Hop  & Destination.

                FD value (Feasiable Distance) = Cost between local router & Destination.

•         DUAL - Diffusion Update Alogrithm

 This a logic which runs on the topology table , elects the best path and put it in Routing table.

              Rule 1:- For a path to become a Feasiable Successor its AD value should be less than current FD value .

                Rule 2:- For a path to be consider as a valid path its AD value should be less than two times the current FD value

•         SIA - Stuck in Active -  This is an Issue

If in topology table Feasiable Successor is not present and if Successor goes down then the router will send Queries to all directly connected routers and will remain in SIA till it gets replies all the Queries . Again these Queries are not bounded to AS . Hence there would be an available route but still it will remain in SIA .

•         Solution for SIA

                1) Summarization

                 2) EIGRP Stub - That router should have single exit point and hence once it is made EIGRP Stub it will tell dont send me Query because I am learning routes from you only.

EIGRP stub options -RCSS

1)receive-only - Prevents the stub from sending any type of route.

2)connected - Permits the stub to send connected routes (may still need to redistribute)

3)static - Permits the stub to send static routes (may still need to redistribute)

4)summary - Permits stub to send summary route

Default is connected and summary

•         Configuration

R1(Config)#router eigrp 100

                         network 11.0.0.0 255.2555.255.0

                         network 12.0.0.0 0.0.0.255

R1# sh ip route

     # sh ip eigrp interface

     # sh ip eigrp neighbor

    # sh ip eigrp topology

•         In EIGRP passive route means good and active route means bad.

•         An EIGRP interface can be configured as Passive so that it wont send and receive update on that interface.

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