BGP communities
Fabiano D'Agostino
fabiano.dagostino96 at gmail.com
Mon Apr 6 22:32:41 CEST 2020
Thank you I was able to solve in this way:
My testing network is made up of router server (as1), router2(as2), router3
(as3).
The goal: as2's routes don't have to be announced to as3
route server conf:
function bgp_out(int peerID)
{
if(0,peerID) ~ bgp_community then return false;
return true;
}
protocol pipe as2 {
import something;
export where bgp_out(2);
}
protocol bgp { ipv4 {import/export all;}}
router2 config:
protocol bgp {
ipv4 {
import all;
export filter {bgp_community.add((0,3)); };
}
}
With this configuration AS3 doesn't receive AS2's routes anymore. But I
have a question, why the if condition is true? It should be if (0,2) ~ (is
inside) [(0,3),..], isn't it?
Thanks,
Il giorno lun 6 apr 2020 alle ore 21:06 Alexander Zubkov <green at qrator.net>
ha scritto:
> 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
>
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