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@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@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