cannot export routes (AS_PATH problem ?)

[Julien Sansonnens]

Hi Kurt,

Thanks a lot for your reply.

I understand the logic, but I'm sure there must be a way to choose the
routes one want to export?

Imagine I have two upstreams, and two peered networks (say: customers).
Both upstreams provide me with a (kind of) full table.

I would like to export the table I get from upstream 1 to peer 1, and the
table from upstream 2 to client 2 (regardless if it's the best route or
not...)

An "export all" is not a solution, since the packets will be redirected to
one or the other upstream according to the best routes algorithm.

thanks  Julien




Le ven. 4 janv. 2019 à 12:18, Kurt Wauters <kuwauters at gmail.com> a écrit :

> Hi Julien,
>
> It probably comes down to one of the standard BGP rules. Community adding
> and filtering seem to be ok but you only advertise the routes that are
> "best" or for which you've got an entry in your routing table.
> If you have multiple upstreams connected the routes are probably spread
> over your upstreams because they all have different flavours of policy and
> peering agreements.
>
> Kind regards
> Kurt
>
> On Fri, Jan 4, 2019 at 8:46 AM Julien Sansonnens <julien at jsansonnens.ch>
> wrote:
>
>> Hi,
>>
>> Using BIRD 1.6.4 I want to do something very basic: export routes to a
>> peer to allow transit.
>>
>> for that, I start by adding communities to my received routes, so I can
>> distinguish the upstream.
>>
>> import filter {
>> if !is_martian() && !is_self_net() && from = bgp_next_hop then {
>> bgp_large_community.add((myas, 100, XX)); #XX for each upstream
>> accept;
>> }
>> else reject;
>> };
>>
>> A community is (apparently?) added to each route. I get about 61'000 ipv6
>> routes from my upstream.
>>
>> Now I want to export them to "peer1". Here is my export function:
>>
>> function bgp_export_peer (){
>> if (myas,100,20) ~ bgp_large_community then return true;
>> }
>>
>> here is the problem: it looks like only 123 routes are exported !
>> bird> show route export peer count
>> 123 of 362489 routes for 61724 networks
>>
>> Here is an example of an exported route:
>>
>> 2001:9d8:200b::/48 via 2a06:1287:3308:c0c0::1 on peer-mmnetworks [mmnet
>> 22:24:20] * (100) [AS25577i]
>>         Type: BGP unicast univ
>>         BGP.origin: IGP
>>         BGP.as_path: 207149 206499 204893 206313 6724 8560 25577
>>         BGP.next_hop: 2a0c:b640:fffe:10:192:220:4:2
>>         BGP.local_pref: 100
>>         BGP.community: (666,666) (997,6499) (6724,900) (6724,960)
>> (8560,4) (8560,10000) (57555,0) (57555,4100) (57555,4101) (65010,10000)
>>         BGP.large_community: (206313, 206313, 206313) (207149, 100, 20)
>>
>> and an example of a non-exported route:
>>
>> 2406:3003:2032::/48 via 2a06:1287:3308:c0c0::1 on peer-mmnetworks [mmnet
>> 20:48:51] (100) [AS55430i]
>>         Type: BGP unicast univ
>>         BGP.origin: IGP
>>         BGP.as_path: 206499 6939 38861 55430
>>         BGP.next_hop: 2a06:1287:3308:c0c0::1 fe80::b9d7:d605
>>         BGP.med: 0
>>         BGP.local_pref: 100
>>         BGP.community: (0,2906) (0,6939) (0,12876) (0,12989) (0,13335)
>> (0,15133) (0,15169) (0,16265) (0,16276) (0,16509) (0,20940) (0,22822)
>> (0,32934)
>>         BGP.large_community: (207149, 100, 20)
>>
>> as you see, my lare community are added on both routes.
>> The exported route has my AS as the first value on the left (AS_PATH),
>> which is not the case for the non-exported route.
>>
>> Logically, all exported routes should have my AS on the left. Am I
>> missing something? It's probably logical, but I do not understand what's
>> going on here.
>> In the same way, I can not export any route that comes from my peers
>> (direct connection), since they have only their AS in the path.
>>
>> help would be highly appreciated.
>> cheers, Julien Sansonnens
>>
>>
>>
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