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BGP question - need help !!!

Hi,

I'm having 2 routers conencting to separate isp, these 2 routers are running egp to the isp and running ibgp between them.

ISP A (AS100) ISP B (AS200) | | | | rtr A (AS900) -- ibgp -- rtr B (AS900) *It uses ISPA ip block and receive full routes from both isps. Two routers are running hsrp, NO OSPF or other internal routing protocol is running between them.

Rtr A

router bgp 900 no synchronization bgp log-neighbor-changes bgp bestpath compare-routerid bgp dampening network 10.1.1.0 neighbor 20.6.6.7 remote-as 100 neighbor 20.6.6.7 soft-reconfiguration inbound neighbor 20.6.6.7 filter-list 1 out neighbor 10.1.1.1 remote-as 900 neighbor 10.1.1.1 next-hop-self

Rtr B

router bgp 900 no synchronization bgp log-neighbor-changes bgp bestpath compare-routerid bgp dampening network 10.1.1.0 neighbor 30.6.6.7 remote-as 200 neighbor 30.6.6.7 soft-reconfiguration inbound neighbor 30.6.6.7 filter-list 1 out neighbor 10.1.1.2 remote-as 900 neighbor 10.1.1.2 next-hop-self

- My problem now is : when I checked rtr A routing table (sh ip bgp), it doesn't receive all the route from Rtr B. Some specific dest (e.g.

12.8.1.0) only shows one best route via isp A, the route via Rtr B doesn't appear in routing table. Why Rtr A behaves differently ?

- when I check routing table on Rtr B, I could see all the route received from Rtr A and every destination has two routing path.

- In case ISP A failure (Rtr A is still up & running), will this route

- 12.8.1.0. failover to Rtr B automatically ?

- when I type sh ip bgp 12.8.1.0 on Rtr B, I could see following 'Advertised to upadte-groups' info. :

BGP routing table entry for 12.8.1.0/23, version 24780039 Paths: (2 available, best #2, table Default-IP-Routing-Table) Advertised to update-groups: 2

- When I type th same on Rtr A, it shows following 'Advertised to non-peer group peers' :

BGP routing table entry for 12.8.1.0/23, version 29880351 Paths: (2 available, best #2, table Default-IP-Routing-Table) Advertised to non peer-group peers:

- why Rtr A does not accept the parameter of 'updated-group'. When 2 routers establish ibgp, they should under the same peer group. Why does Rtr A shows 'Advertised to updated-groups', while Rtr B shows 'Advertised to non peer-group peers' ? Does it mean my ibgp configuration is incompleted ?

Many thanks in advance :-)

Reply to
yellow
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- My problem now is : when I checked rtr A routing table (sh ip bgp), it doesn't receive all the route from Rtr B. Some specific dest (e.g.

12.8.1.0) only shows one best route via isp A, the route via Rtr B doesn't appear in routing table. Why Rtr A behaves differently ?

Router B has the better path, therefore router A doesn't populate it's BGP or routing table with that update.

- In case ISP A failure (Rtr A is still up & running), will this route

- 12.8.1.0. failover to Rtr B automatically ?

I believe it will, but I always tell my customers that the best way to determine this is to schedule downtime and do a failover test.

Regards, Steve

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Reply to
www.networking-forum.com

In BGP, you only advertise the best route to your neighbors. Since B considers the route it learned from A to be better than the one it learned from the ISP, it doesn't advertise the ISP route back to A.

The ISP A routes are all better than the ISP B routes, so Rtr A advertises all its routes to Rtr B.

Yes. When the connection to ISP A goes down, Rtr A will withdraw its routes from its advertisements. Then Rtr B's best (and only) routes will be the ones it learned from ISP B, so it will advertise them to Rtr A.

I didn't see anything about peer groups in the BGP configurations you posted.

Reply to
Barry Margolin

Barry Margolin =E5=AF=AB=E9=81=93=EF=BC=9A

Hi, If i don't setup peer group, will it affect the failover function & route updates between these two routers ? If my site only has 2 Rtrs, do you still suggest to use peer group ?

Thanks, Thanks

Reply to
yellow

Peer groups are useful when you have several neighbors that you want to use the same options with. You list the options in the peer group configuration, and then use "neighbor x.x.x.x peer-group XXXX" for each neighbor. If you only have two routers, there's no need for peer groups.

P.S. Did you really need to quote *everything* just to ask this question?

Reply to
Barry Margolin

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