BGP link reroute problem

BGP link reroute problem
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Subject Author Date
BGP link reroute problem response3 08-24-2006
Posted by response3 on August 24, 2006, 1:41 pm
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Hi all. I'm learning BGP for my CCNP BSCI exam, and have been trying
to setup a test lab with 3 routers in a full mesh. I've got each
router speaking BGP to each other and advertising a local subnet to
each other (the subnet is setup on a loopback interface instead of a
physical interface). If I do a "show ip bgp", I can see two paths to
each subnet, and a "show ip route" tells me the same thing. The
problem is when I take down the link from router A to C, the traffic
from router A cannot pass through router B to the loopback interface on
router C. I've looked and looked, and it's probably simple, but I
don't understand what's preventing ping traffic from passing through
the alternate routes. If you help out and possibly give a few
suggestions, I'd really appreciate it! Thanks.


Posted by Doan on August 24, 2006, 3:56 pm
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On 24 Aug 2006, response3 wrote:

> Hi all. I'm learning BGP for my CCNP BSCI exam, and have been trying
> to setup a test lab with 3 routers in a full mesh. I've got each
> router speaking BGP to each other and advertising a local subnet to
> each other (the subnet is setup on a loopback interface instead of a
> physical interface). If I do a "show ip bgp", I can see two paths to
> each subnet, and a "show ip route" tells me the same thing. The
> problem is when I take down the link from router A to C, the traffic
> from router A cannot pass through router B to the loopback interface on
> router C. I've looked and looked, and it's probably simple, but I
> don't understand what's preventing ping traffic from passing through
> the alternate routes. If you help out and possibly give a few
> suggestions, I'd really appreciate it! Thanks.
>
Can you post your configurations and "show ip route" of each router?

Doan



Posted by NO_spamm on August 24, 2006, 4:29 pm
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On Thu, 24 Aug 2006 10:41:23 -0700, response3 wrote:

> Hi all. I'm learning BGP for my CCNP BSCI exam, and have been trying
> to setup a test lab with 3 routers in a full mesh. I've got each
> router speaking BGP to each other and advertising a local subnet to
> each other (the subnet is setup on a loopback interface instead of a
> physical interface). If I do a "show ip bgp", I can see two paths to
> each subnet, and a "show ip route" tells me the same thing. The
> problem is when I take down the link from router A to C, the traffic
> from router A cannot pass through router B to the loopback interface on
> router C. I've looked and looked, and it's probably simple, but I
> don't understand what's preventing ping traffic from passing through
> the alternate routes. If you help out and possibly give a few
> suggestions, I'd really appreciate it! Thanks.

The questions that need to be answered are:

- did you configure iBGP or eBGP or a combination?
- did you configure an IGP (OSPF, ISIS, etc)?
- did you use loopbacks as neighbor addresses?




FW

Posted by response3 on August 26, 2006, 4:46 am
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NO_spamm wrote:
> On Thu, 24 Aug 2006 10:41:23 -0700, response3 wrote:
>
> > Hi all. I'm learning BGP for my CCNP BSCI exam, and have been trying
> > to setup a test lab with 3 routers in a full mesh. I've got each
> > router speaking BGP to each other and advertising a local subnet to
> > each other (the subnet is setup on a loopback interface instead of a
> > physical interface). If I do a "show ip bgp", I can see two paths to
> > each subnet, and a "show ip route" tells me the same thing. The
> > problem is when I take down the link from router A to C, the traffic
> > from router A cannot pass through router B to the loopback interface on
> > router C. I've looked and looked, and it's probably simple, but I
> > don't understand what's preventing ping traffic from passing through
> > the alternate routes. If you help out and possibly give a few
> > suggestions, I'd really appreciate it! Thanks.
>
> The questions that need to be answered are:
>
> - did you configure iBGP or eBGP or a combination?
> - did you configure an IGP (OSPF, ISIS, etc)?
> - did you use loopbacks as neighbor addresses?
>
>
>
>
> FW

Here's the configs. Thanks all.

############################

R1
lo0: 192.168.1.1
s0: 10.1.1.1
fa0: 10.3.3.1

Router bgp 1
Network 192.168.1.0 mask 255.255.255.0
Neighbor 10.3.3.2 remote-as 3
Neighbor 10.1.1.2 remote-as 2

------------------------------------

R2
lo0: 192.168.2.1
s0: 10.1.1.2
fa0: 10.2.2.1

Router bgp 2
Network 192.168.2.0 mask 255.255.255.0
Neighbor 10.3.3.2 remote-as 3
Neighbor 10.1.1.1 remote-as 1

-------------------------------------

R3
gi0/0: 10.3.3.2
gi0/1: 10.2.2.2
lo0: 192.168.3.1

Router bgp 3
Network 192.168.3.0 mask 255.255.255.0
Neighbor 10.3.3.1 remote-as 1
Neighbor 10.1.1.2 remote-as 2


###################

Hope this helps. Thanks again.

-Brian


Posted by NO_spamm on August 26, 2006, 10:49 am
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On Sat, 26 Aug 2006 01:46:41 -0700, response3 wrote:

>
> NO_spamm wrote:
>> On Thu, 24 Aug 2006 10:41:23 -0700, response3 wrote:
>>
>> > Hi all. I'm learning BGP for my CCNP BSCI exam, and have been trying
>> > to setup a test lab with 3 routers in a full mesh. I've got each
>> > router speaking BGP to each other and advertising a local subnet to
>> > each other (the subnet is setup on a loopback interface instead of a
>> > physical interface). If I do a "show ip bgp", I can see two paths to
>> > each subnet, and a "show ip route" tells me the same thing. The
>> > problem is when I take down the link from router A to C, the traffic
>> > from router A cannot pass through router B to the loopback interface on
>> > router C. I've looked and looked, and it's probably simple, but I
>> > don't understand what's preventing ping traffic from passing through
>> > the alternate routes. If you help out and possibly give a few
>> > suggestions, I'd really appreciate it! Thanks.
>>
>> The questions that need to be answered are:
>>
>> - did you configure iBGP or eBGP or a combination?
>> - did you configure an IGP (OSPF, ISIS, etc)?
>> - did you use loopbacks as neighbor addresses?
>>
>>
>>
>>
>> FW
>
> Here's the configs. Thanks all.
>
> ############################
>
> R1
> lo0: 192.168.1.1
> s0: 10.1.1.1
> fa0: 10.3.3.1
>
> Router bgp 1
> Network 192.168.1.0 mask 255.255.255.0
> Neighbor 10.3.3.2 remote-as 3
> Neighbor 10.1.1.2 remote-as 2
>
> ------------------------------------
>
> R2
> lo0: 192.168.2.1
> s0: 10.1.1.2
> fa0: 10.2.2.1
>
> Router bgp 2
> Network 192.168.2.0 mask 255.255.255.0
> Neighbor 10.3.3.2 remote-as 3
> Neighbor 10.1.1.1 remote-as 1
>
> -------------------------------------
>
> R3
> gi0/0: 10.3.3.2
> gi0/1: 10.2.2.2
> lo0: 192.168.3.1
>
> Router bgp 3
> Network 192.168.3.0 mask 255.255.255.0
> Neighbor 10.3.3.1 remote-as 1
> Neighbor 10.1.1.2 remote-as 2
>
>
> ###################
>
> Hope this helps. Thanks again.
>
> -Brian


Try, to disable synchronization on all three routers:

router bgp n
no synch


FW

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