routes with iBGP

[Arjan Filius]

Hello Ondrej, bird-users.


Thanks for your explanation.

hereby the output of the "show route 40.0.40.0/21 all" on both routers. (ip's scrambled)
The second transit has one AS hop extra (5) where the first transit has 
only 4 AS hops. which makes is valid to me, to let router2 choose the 
patch via router1.


router1#

BIRD 1.2.3 ready.
bird> show route 40.0.40.0/21 all
40.0.40.0/21       via <Transit1_BGPRTR1> on eth5 [Transit1_BGPRTR1_IPv4 2010-06-04 11:26:29] * (100) [AS4249i]
         Type: BGP unicast univ
         BGP.origin: IGP
         BGP.as_path: 24785 3356 7332 4249
         BGP.next_hop: <Transit1_BGPRTR1>
         BGP.med: 40231
         BGP.local_pref: 100
                    via <Transit1_BGPRTR2> on eth5 [Transit1_BGPRTR2_IPv4 2010-06-04 11:26:39] (100) [AS4249i]
         Type: BGP unicast univ
         BGP.origin: IGP
         BGP.as_path: 24785 3356 7332 4249
         BGP.next_hop: <Transit1_BGPRTR2>
         BGP.med: 40231
         BGP.local_pref: 100
bird>


router2#

BIRD 1.2.3 ready.
bird> show route 40.0.40.0/21 all
40.0.40.0/21       via <gw1_router1> on eth1 [iBGP_IPv4_1 2010-06-08 13:39:27] * (100) [AS4249i]
         Type: BGP unicast univ
         BGP.origin: IGP
         BGP.as_path: 24785 3356 7332 4249
         BGP.next_hop: <gw1_router1>
         BGP.med: 40231
         BGP.local_pref: 100
                    via <gw1_router2> on eth0 [iBGP_IPv4_2 2010-06-08 13:28:18] (100) [AS4249i]
         Type: BGP unicast univ
         BGP.origin: IGP
         BGP.as_path: 24785 3356 7332 4249
         BGP.next_hop: <gw1_router2>
         BGP.med: 40231
         BGP.local_pref: 100
                    via <Transit2_BGPRTR1> on eth5 [Transit2_BGPRTR1_IPv4 2010-06-04 11:26:30] (100) [AS4249i]
         Type: BGP unicast univ
         BGP.origin: IGP
         BGP.as_path: 38930 1299 3356 7332 4249
         BGP.next_hop: <Transit2_BGPRTR1>
         BGP.local_pref: 100
bird>


Regards,



On Tue, 8 Jun 2010, Ondrej Zajicek wrote:

> On Tue, Jun 08, 2010 at 02:15:07PM +0200, Arjan Filius wrote:
>> Hello bird-users,
>>
>> Running bird 1.2.3-ppa ubuntu 10.04,x64, on 2 hosts, internally connected
>> with 2 lines, and running 2 iBGP sessions, both routers have their own
>> GlobalTransit provider
>>
>> the iBGP protocols have no filters on both routers
>>
>> What is noticed (for example with network 40.0.40.0/21):
>> router1:
>> bird> show route 40.0.40.0/21
>> 40.0.40.0/21       via <Transit1_BGPRTR1> on eth5 [Transit1_BGPRTR1_IPv4 2010-06-04 11:26:29] * (100) [AS4249i]
>>                    via <Transit1_BGPRTR2> on eth5 [Transit1_BGPRTR2_IPv4 2010-06-04 11:26:39] (100) [AS4249i]
>> bird>
>>
>> router2:
>> bird> show route 40.0.40.0/21
>> 40.0.40.0/21       via <gw1_router1> on eth1 [iBGP_IPv4_1 2010-06-08  13:39:27] * (100) [AS4249i]
>>                    via <gw2_router1> on eth0 [iBGP_IPv4_2 2010-06-08  13:28:18] (100) [AS4249i]
>>                    via <Transit2_BGPRTR1> on eth5 [Transit1_BGPRTR1_IPv4
>> 2010-06-04 11:26:30] (100) [AS4249i] bird>
>>
>> so router1 isn't showing it's route option to a transit on router2 (via 2
>> iBGP sessions)
>
>>
>> Is this correct, end if yes why?
>
> It is correct because in router2, iBGP route received from router1 is
> primary and therefore it is not exported back back to router1 (and only
> the primary route is exported).
>
> But the question is why internal route is primary (usually, external
> routes are primary). Could you send the output of 'show route 40.0.40.0/21 all'
> on router2?
>
>

-- 
Arjan Filius
mailto:iafilius at xs4all.nl