BGP Local Preference
on the diagram below we can make R4 choose R3 instead of R2 to get to Network 1.1.1.0/24 behind R1
However, what if we have R5 on AS2 that has one link connected to R4 and one link connected to R2, then is R5 will choose R4 to get to 1.1.1.0/24 or it will choose R2 ?
R3(config)# route-map LocalPref permit 10
R3(config-route-map)#set local-preference 700
R3(config)# Router bgp 2
R3(config-router)neighbor 192.168.13.1 route-map LocalPref in
However, what if we have R5 on AS2 that has one link connected to R4 and one link connected to R2, then is R5 will choose R4 to get to 1.1.1.0/24 or it will choose R2 ?
R3(config)# route-map LocalPref permit 10
R3(config-route-map)#set local-preference 700
R3(config)# Router bgp 2
R3(config-router)neighbor 192.168.13.1 route-map LocalPref in
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ASKER
do you mean, they need to be as shown below:
ASKER
instead of physical Full Mesh: N(N-1)/2 Links we can use:
BGP Confederation OR Route Reflector
BGP Confederation OR Route Reflector
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Thanks
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All BGP nodes inside of the same AS need be connected in full mesh. R4 when receives NLRIs from eBGP neighbors will never advertise those to another iBGP neighbor. NLRIs will be advertised only to directly connected eBGP neighbors. So, even if link between R5 and R3 do not exist you still need to configure R5 as neighbor for all other routers in the same AS (R2, R3 & R4 need to be configured as BGP peers for R5 even if some physical link is missing (physical link between R5 & R3)). Additionally BGP is relying on IGP to provide routes how to reach BGP peers.
There are 2 ways to go around full mesh rule:
- BGP route reflectors
- BGP confederations
But again, those are ways to reduce number of peering inside of AS and still have a "full mesh".