Route Selection Cisco Routers

Route Selection Cisco Routersroute selection cisco routers

Case :-   

All of the routers R1 R2 R3 R4 are running EIGRP , RIPv2, BGP and advertising all of its local subnets.

R1, R2 , R3 are in BGP AS 100 . R3 is running BGP as 300

R1-R2 is IBGP , R2-R4 is IBGP. R1-R3 is EBGP , R3-R4 is EBGP

R1 and R4 have been configured as route reflector clients at Router R2 so that information of 10.10.10.10/32 can get advertised to R1.

Question is thru which protocol you will see 10.10.10.10/32 in routing table of Router R1 or what will be the AD value of 10.10.10.10/32 network in Router R1.

Solution:-

Route Selection Cisco Routers.

EIGRP and RIPv2 is running on all routers so R1 will have 10.10.10.10/32 thru EIGRP with AD 90 and RIP with AD 120.

By default, network information advertised by one IBGP peer can not be advertised to other IBGP Peer. So to make it happen, route reflector client is also configured at Router R2 for clients 20.1.1.1 and client 40.1.1.2. So Router R1 will have 10.10.10.10/32 learned thru IBGP as well with AD 200

R1 will not be able to learn 10.10.10.10/32 thru EBGP peer 30.1.1.2. Reason is that when 10.10.10.10/32 initially travelled from Router R4 its AS was 100. When it reached R3 , it added AS 300 in its AS tracker. When it reached R1 it found itself again in AS 100. So its AS Path became 100, 300, 100 and due to AS Path loop avoiding mechanism , 10.10.10.10/32 did not get installed.

So Routing protocol comparison was to happen between RIPv2( AD 120), EIGRP ( AD 90) , IBGP( AD 200). Therefore, lowest AD won the election. Therefore, In router R1 we will see 10.10.10.10/32 installed thru EIGRP i.e. keyword “D” with AD 90.

To be able to understand routing problems – you should have thorough knowledge of Networking Concepts. So This case of Route Selection Cisco Routers will make your job easy for sure.

 

 
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