On Mar 26, 2017, at 10:16 AM, Alarig Le Lay <alarig@swordarmor.fr> wrote:

On dim. 26 mars 09:08:25 2017, Michael McConnell wrote:

Hello all,

We are running into an issue transiting a down stream ASN. E.g. Uplink
<-> Our ASN <-> Downlink ASN

To me it seems we should only need to bgp_path.prepend our outbound
filter, however our uplink is dropping the as path when we run it that
way.

Any suggestions as to what I am missing to carrier a downstream ASN
and prefixes to our uplinks?

Thanks so much,
Mike

Hi, why do you want to bgp_path.prepend? Your ASN will be automatically
added in the path if you act as transit between upstream and downstream
AS.

Exemple:

template bgp DOWNSTREAM {
import keep filtered;
export all;
}

function bgp_filter_customer_in (prefix customer_prefix) {
       if ! (net ~ customer_prefix) then return false;
       else return true;
}

filter bgp_filter_customer_petrus_in {
       if (bgp_filter_customer_in(2001:678:3cc::/48)) then accept;
       else reject "Prefix filtered for petrus";
}


protocol bgp bgp_petrus from DOWNSTREAM {
       local as 204092;
       description "BGP for petrus";
neighbor 2a00:5884::25 as 206155;
       import keep filtered;
       import filter bgp_filter_customer_petrus_in;
}


And from another router, we see that:
bird> show route all protocol bgp_grifon_nominoe
2a00:5884::/32     via 2001:7f8:b1::a on eth2 [bgp_grifon_nominoe 12:41:15] (100) [AS204092i]
Type: BGP unicast univ
BGP.origin: IGP
BGP.as_path: 204092
BGP.next_hop: 2001:7f8:b1::a fe80::215:17ff:fe39:f01a
BGP.local_pref: 100
2001:678:3cc::/48  via 2001:7f8:b1::a on eth2 [bgp_grifon_nominoe 12:41:15] (100) [AS206155i]
Type: BGP unicast univ
BGP.origin: IGP
BGP.as_path: 204092 206155
BGP.next_hop: 2001:7f8:b1::a fe80::215:17ff:fe39:f01a
BGP.local_pref: 100

So, we have our prefix with just our ASN, and 2001:678:3cc::/48 with our
and the customer ASN.

--
alarig