[j-nsp] Hidden IPv4 iBGP routes

[John Neiberger]

Something that makes this a little stranger to me is that in the
output showing the looped AS, the local AS isn't ever listed. The
route is originating in AS YYYYY and passing through AS XXXXX on the
way to this router, which is in AS ZZZZZ. I'm confused about how an AS
path loop could be happening.

[YYYYY] -- ebgp -- [XXXXX] -- ebgp -- [ ZZZZZ] -- ibgp/rr -- [juniper router]

The Juniper box is an RR client of the upstream router, which in turn
is an eBGP peer with XXXXX who is learning a route from YYYYY. I don't
see how a path loop could form. I suspect something is just
misconfigured somewhere.

On Tue, Mar 13, 2012 at 3:37 PM, David Miller <dmiller at tiggee.com> wrote:
> On 3/13/2012 4:15 PM, Stefan Fouant wrote:
>> Yes this is correct and is indeed the default Junos behavior. If you wanted to receive a looped BGP update, you can define the amount of loops allowed (.i.e. number of times your own AS appears in the AS Path attribute) by configuring the 'set routing-options autonomous system <as-num> loops <num>' command.
>>
>> HTHs.
>>
>> Stefan Fouant
>> JNCIE-SEC, JNCIE-SP, JNCIE-ER, JNCI
>> Technical Trainer, Juniper Networks
>>
>> Follow us on Twitter @JuniperEducate
>>
>> Sent from my iPad
>
> You can also allow loops on a per BGP neighbor basis with:
>
> neighbor 10.0.0.1 {
>    family inet {
>        unicast {
>            loops 1;
>        }
>    }
> }
>
> -DMM
>
>> On Mar 13, 2012, at 4:10 PM, "Mohammad" <masalbad at gmail.com> wrote:
>>
>>> Hi john;
>>>
>>>
>>>
>>> As far as I know when an  eBGP router receives a route contains its own AS
>>> in the AS path it consider it as a loop, so for your case the juniper router
>>> is seeing its own AS (XXXX) in the route's ASPATH received from its eBGP
>>> neighbor (XXXXX  YYYYY I), so the solution I would suggest is to remove AS
>>> XXXX on the other router before sending it to the juniper router, if XXXX is
>>> a private AS you can use remove private on the other router; or you can use
>>> AS override.
>>>
>>> Hope it is helpful;
>>> Mohammad Salbad
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