BGP communities

[Alexander Zubkov]

You have to configure export filter with something like:
bgp_community.add((x,y));
This is for community written as x:y on most hardware routers.

On Mon, Apr 6, 2020 at 8:57 PM Fabiano D'Agostino
<fabiano.dagostino96 at gmail.com> wrote:
>
> Thanks for your helping,
> How do I set in my router (AS2) the community to the exported routes? I don't understand this.
>
>
>
> Il giorno lun 6 apr 2020 alle ore 20:26 Alexander Zubkov <green at qrator.net> ha scritto:
>>
>> OK. So you have some route x.x.x.x/y that you receive from AS2 by
>> protocol bgp pb_0002_as2?
>>
>> 1) it is received via bgp pb_0002_as2 into table t_0002_as2
>> 2) it is piped from table t_0002_as2 to master4 with filter
>> f_export_to_master (missing in your config)
>> 3) it is piped from table master4 to t_0005_as3 with filter where
>> ixp_community_filter(3) (ixp_community_filter is also missing)
>> 4) it is exported to bgp pb_0005_as3
>>
>> At which point do you think it should be filtered and why?
>> As I see, your routers (AS2) do not set any communities to the
>> exported routes, so if you do not set them in any of those missing
>> filters, then your check for the presence of the community will not
>> fire.
>>
>> On Mon, Apr 6, 2020 at 7:03 PM Fabiano D'Agostino
>> <fabiano.dagostino96 at gmail.com> wrote:
>> >
>> > This is the bird.conf of the route server:
>> > https://pastebin.com/qwp6nBtz
>> > This is the bird.conf of one router:
>> > https://pastebin.com/trwgKG92
>> >
>> > Why does AS3 still receive routes from AS2? What am I missing?
>> >
>> > Thanks,
>> >
>> > Il giorno lun 6 apr 2020 alle ore 18:13 Alexander Zubkov <green at qrator.net> ha scritto:
>> >>
>> >> It is really hard to guess what routes you have actually in your
>> >> bird's table and how your bird is configured.
>> >>
>> >> > I just edited the bird.conf of the route server, should I also edit the bird.conf of the routers which are peering with the route server?
>> >>
>> >> Filters on peers can affect only communities you are sending and other
>> >> attributes, but they do not affect directly the logic of your route
>> >> server's filters, there is no magic here.
>> >>
>> >> On Mon, Apr 6, 2020 at 6:08 PM Fabiano D'Agostino
>> >> <fabiano.dagostino96 at gmail.com> wrote:
>> >> >
>> >> > Does 'show route where' exist as command? Because I have syntax error.
>> >> > Anyway I set up my route server as here:
>> >> > https://www.slideshare.net/apnic/bird-routing-daemon
>> >> > But I am having the problem described here:
>> >> > https://bird.network.cz/pipermail/bird-users/2010-September/001620.html
>> >> >
>> >> > I just edited the bird.conf of the route server, should I also edit the bird.conf of the routers which are peering with the route server?
>> >> >
>> >> > Thanks,
>> >> >
>> >> > Il giorno lun 6 apr 2020 alle ore 17:50 Alexander Zubkov <green at qrator.net> ha scritto:
>> >> >>
>> >> >> Have you tried to check that in cli like:
>> >> >> show route where bgp_out(...)
>> >> >> And check that required route has all needed communities:
>> >> >> show route all x.x.x.x/y
>> >> >>
>> >> >> On Mon, Apr 6, 2020 at 5:35 PM Fabiano D'Agostino
>> >> >> <fabiano.dagostino96 at gmail.com> wrote:
>> >> >> >
>> >> >> > Hey,
>> >> >> > thank you! I think I am having the same problem they had here:
>> >> >> > https://bird.network.cz/pipermail/bird-users/2010-September/001620.html
>> >> >> >
>> >> >> > But I didn't understand how they solved.
>> >> >> >
>> >> >> > Regards,
>> >> >> > Fabiano
>> >> >> >
>> >> >> > Il giorno lun 6 apr 2020 alle ore 17:16 Cybertinus <bird at cybertinus.nl> ha scritto:
>> >> >> >>
>> >> >> >> Hello Fabiano,
>> >> >> >>
>> >> >> >>
>> >> >> >> BGP Communities are basically tags you add to a prefix that is received from, or send to, a peer. And in Bird you can do whatever you want with these communities. A community by itself has no meaning and has no influence on the routing decision whatsoever. It is the meaning you add to it in your configuration what makes them work.
>> >> >> >>
>> >> >> >> More information about communities: https://en.wikipedia.org/wiki/Border_Gateway_Protocol#Communities
>> >> >> >>
>> >> >> >>
>> >> >> >> Kind regards,
>> >> >> >> Cybertinus
>> >> >> >>
>> >> >> >>
>> >> >> >> On 2020-04-06 17:03, Fabiano D'Agostino wrote:
>> >> >> >>
>> >> >> >> and how these kind of checks are handled?
>> >> >> >> if (myas,peeras) ~ bgp_community  what is bgp_community?
>> >> >> >>
>> >> >> >> Thanks,
>> >> >> >>
>> >> >> >> Il giorno lun 6 apr 2020 alle ore 15:32 Fabiano D'Agostino <fabiano.dagostino96 at gmail.com> ha scritto:
>> >> >> >>
>> >> >> >> Thank you, but "if the route does not come from BGP then false"
>> >> >> >> here I have:
>> >> >> >> protocol pipe a {
>> >> >> >>     table master;
>> >> >> >>     mode transparent;
>> >> >> >>     peer table a;
>> >> >> >>     import all;
>> >> >> >>     export where bgp_out(x); => this becomes false, what does this mean?
>> >> >> >>     #export all;
>> >> >> >> }
>> >> >> >>
>> >> >> >> Thanks,
>> >> >> >>
>> >> >> >> Il giorno lun 6 apr 2020 alle ore 10:50 Bernd Naumann <bena at spreadshirt.net> ha scritto:
>> >> >> >>
>> >> >> >> On 05.04.20 23:08, Fabiano D'Agostino wrote:
>> >> >> >> > Good evening,
>> >> >> >> > could someone explain me the meaning of these lines?
>> >> >> >> >
>> >> >> >> > function bgp_out(int peeras)
>> >> >> >> > {
>> >> >> >> > if ! (source = RTS_BGP ) then return false;
>> >> >> >> > if peeras > 65535 then return true; ### communities do not support AS32
>> >> >> >> > if (0,peeras) ~ bgp_community then return false;
>> >> >> >> > if (myas,peeras) ~ bgp_community then return true;
>> >> >> >> > if (0, myas) ~ bgp_community then return false;
>> >> >> >> > return true;
>> >> >> >> > }
>> >> >> >> >
>> >> >> >> > Thanks,
>> >> >> >> >
>> >> >> >> > Fabiano
>> >> >> >> >
>> >> >> >>
>> >> >> >> Morning,
>> >> >> >>
>> >> >> >> I can not cover the whole section but as a start...
>> >> >> >>
>> >> >> >> * if the route does not come from BGP then false (routing table source?)
>> >> >> >> * if the remote AS Number is greater 65535 (16 Bit) then "just" return
>> >> >> >> true (see AS 32 Bit Numbers, and the non-support of older
>> >> >> >> devices/implementations)
>> >> >> >> * For the next 3 I'm not 100% sure how to read but I found
>> >> >> >> https://bird-users.network.narkive.com/3uDbo6H9/any-ix-willing-to-share-their-config
>> >> >> >>
>> >> >> >> ```
>> >> >> >> 0:XXXXX - Do not announce route to peer XXXXX
>> >> >> >> 0:MyASN - Do not announce route to all peers
>> >> >> >> MyASN:XXXXX - Announce route to peer XXXXX only
>> >> >> >> MyASN:MyASN - Announce routes to all peers. This community is
>> >> >> >> automatically added to all routes that are not
>> >> >> >> tagged with any of MyASN:XXXXX communities.
>> >> >> >> ```
>> >> >> >>
>> >> >> >> Maybe this helps a little bit.
>> >> >> >>
>> >> >> >> Bernd