Re: Newbie question - create filter for prefixes to export and also modify bgp next hop

[Mathias Wolkert]

On 3/2/11 15:57 , Ondrej Filip wrote:
On 2.3.2011 14:55, Mathias Wolkert wrote:
Hi
On 3/2/11 11:32 , Ondrej Filip wrote:
On 2.3.2011 10:36, Mathias Wolkert wrote:
Hi

As said, I'm new to BIRD and struggling a bit with the config syntax.

I'll try to explain what I want to do.

I have a few prefixes, lets say 10.1.1.0/24, 10.2.2.0/24, 10.3.3.0/24.
I want to announce these (and only these) in a BGP session, but with a
modified next hop.

How would I do this?

Add this export filter to you BGP session:

export filter {
     if net ~ [10.1.1.0/24, 10.2.2.0/24, 10.3.3.0/24] then {
         bgp_next_hop = X.X.X.X;
         accept;
     }
     else reject;
};

(I did not check syntax, maybe some ';' is missing.
         Ondrej

Working fine, thanks a lot.

Now say I want to do this for all my +100 peers could I do the
filtering once in a filter and call that in every session?

Sure, you can just:

filter bgp_out
{
    if net ~ [10.1.1.0/24, 10.2.2.0/24, 10.3.3.0/24] then {
       bgp_next_hop = X.X.X.X;
       accept;
    }
    else reject;
};

And at every BGP session e.g.:

protocol bgp AAAA {
   local as myas;
   neighbor XX.XX.XX.XX as YYYY;
   import all;
   export filter bgp_out;
   rs client;
}

Perfect, that is exactly what I want.

I realize that it's the tildes and types of brackets part that makes me 
uncertain.


Or you can use function that accepts parameters etc.


Another thing.

One of these prefixes I want to originate from a different AS.
In IOS and quagga I can do this with "set as-path prepend" and get:

prefix/mask<local_as>  <prepended_as>  i


Are you sure? This looks wrong to me.

Doing this in BIRD gives me a different behavior and I get:

prefix/mask<prepended_as>  <local_as>  i

A little bird told me about this not beeing wrong, but closer to what
the standard states.

Do you agree?
How would I get around this, another table and pipes?

So you would like to change originator? Which way? YOU would like to
be an originator?

Yes, I'd like to change the originator to "prepended_as" and also have 
"local_as" in the path like I have on quagga/IOS.

I've been told Cisco is breaking the standard by not appending but 
replace the as-path when originating prefixes.

Not sure myself...


                        Ondrej



/Tias





Any help is much appreciated.

/Tias



/Tias