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New Member

bgp path selection issue

hi,

i have the following cli show command output,

R2#show bgp ipv4 unicast
BGP table version is 11, local router ID is 192.168.220.252
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
              r RIB-failure, S Stale
Origin codes: i - IGP, e - EGP, ? - incomplete

   Network          Next Hop            Metric LocPrf Weight Path
* i192.168.30.0     192.168.110.70           0    100      0 63000 i
*>                  192.168.220.70           0             0 63000 63000 i
* i192.168.40.0     192.168.110.70           0    100      0 63000 63000 i
*>                  192.168.220.70           0             0 63000 i
R2#

why isn't the route through the shortest AS path not selected as the best route for 192.168.30.0. ?

 

thanks,

uddika

Everyone's tags (1)
2 ACCEPTED SOLUTIONS

Accepted Solutions

It seems that one is ibgp

It seems that one is ibgp learnt route. Please show the output form the command show ip bgp 192.168.30.0.

Hall of Fame Super Silver

Hello Uddika,yes use of next

Hello Uddika,

yes use of next-hop-self is a good practice.

However, there are two other options:

a) to have each border router to advertise its own border link(s) subnet(s) in iBGP with a network command under BGP process

b) to use an IGP like OSPF with the passive-interface option to make border links connecting to other ASes known to other iBGP speakers as IP subnets.

 

Hope to help

Giuseppe

 

 

10 REPLIES

It seems that one is ibgp

It seems that one is ibgp learnt route. Please show the output form the command show ip bgp 192.168.30.0.

New Member

R2#R2#R2#show ip bgp 192.168

R2#
R2#
R2#show ip bgp 192.168.30.0
BGP routing table entry for 192.168.30.0/24, version 7
Paths: (2 available, best #2, table Default-IP-Routing-Table)
  Advertised to update-groups:
     2         
  63000
    192.168.110.70 (inaccessible) from 192.168.111.251 (192.168.111.251)
      Origin IGP, metric 0, localpref 100, valid, internal
  63000 63000, (received & used)
    192.168.220.70 from 192.168.220.70 (192.168.220.70)
      Origin IGP, metric 0, localpref 100, valid, external, best
R2#
R2#

thanks, i noticed that R2 does not have the route for the next hop, 192.168.110.70.

 

New Member

i guess the recommended

i guess the recommended configuration is to advertise routes to ibgp peers with next-hope-self, isn't it?

Hall of Fame Super Silver

Hello Uddika,yes use of next

Hello Uddika,

yes use of next-hop-self is a good practice.

However, there are two other options:

a) to have each border router to advertise its own border link(s) subnet(s) in iBGP with a network command under BGP process

b) to use an IGP like OSPF with the passive-interface option to make border links connecting to other ASes known to other iBGP speakers as IP subnets.

 

Hope to help

Giuseppe

 

 

New Member

Hi,        Already the route

Hi,

        Already the route is learned via shortest as path only i think since the route is correctly learned from EBGP nly not IBGP..So why the additional config is required here? pls clarify

Hi, isn't there'bgp bestpath

Hi,

 

isn't there

'bgp bestpath as-path ignore'

configured on the router?

 

Best regards,

Milan

New Member

no,.. i checked that.

no,.. i checked that.

Hi,in that case, can you

Hi,

in that case, can you paste more details?

sh ip bgp 192.168.30.0

output from both R2 and R1 plus BGP config section from both of them?

 

Best regards,

Milan

 

Hello

Hello Try a soft reset and check again Clear ip bgp * soft Res Paul
Please don't forget to rate any posts that have been helpful. Thanks.
New Member

didn't work, even rebooted

didn't work, even rebooted all router.

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