03-29-2012 07:04 AM - edited 03-04-2019 03:50 PM
Hello all,
I hope the diagram explain what it is I am trying to do, I have 4 routers R1 – R4 – R3 and R4 and they receive via EBGP a route to 161.163.160.0/22 this route can be seen in the IP table of each of R1 – 4. I am attempting to install a backup route to this network via R1 by configuring a static route to its WAN connection and then prepending the AS path, this route can be seen in R2 but R2 does not advertise this route to either 3 or 4.
R2>sh ip bgp 161.163.160.0
Multipath: iBGP
Advertised to update-groups:
1
2856 65352 65439, (received & used)
161.163.164.247 (metric 153856) from 161.163.164.247 (161.163.164.247)
Origin incomplete, metric 0, localpref 100, valid, internal, best
Community: 4282908783
2856 65352 65439, (received & used)
161.163.164.249 (metric 154112) from 161.163.164.249 (161.163.164.249)
Origin incomplete, metric 0, localpref 100, valid, internal
Community: 4282908783
65438 65438 65438 65438 65438 65438 65438 65438 65438, (received & used) ••ß PREPENDED route
161.163.164.14 from 161.163.164.14 (161.163.164.244)
Origin IGP, metric 0, localpref 100, valid, external
The prepended route is not advertised
R2>sh ip bgp neighbors 161.163.164.249 advertised-routes | include 161.163.160.0
Thank you,
Jonathan
Solved! Go to Solution.
03-29-2012 07:16 AM
hi Jonathan,
The prepended route is not advertised by R2 to R3 and R4 since this route is also advertised by R3,4 to R2.
The R2 selects the route received by R3,R4 as best, so do not advertise back the route received by the same node (BGP rule).
If R3,R4 does not have the route, they learn the prepended route by R2.
Hope that helps,
Vasilis
03-29-2012 07:16 AM
hi Jonathan,
The prepended route is not advertised by R2 to R3 and R4 since this route is also advertised by R3,4 to R2.
The R2 selects the route received by R3,R4 as best, so do not advertise back the route received by the same node (BGP rule).
If R3,R4 does not have the route, they learn the prepended route by R2.
Hope that helps,
Vasilis
03-29-2012 07:28 AM
It does yes although I think I answered the question myself if I took the time to read my post :-( R2 advertise the route to other peers just not the peers it receives the BEST path from.
Thank you Vasilis
03-29-2012 03:11 PM
You are welcome Jonathan,
Thanks for the rating!
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