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

2 Mar 2011

      On 2.3.2011 14:55, Mathias Wolkert wrote:
...
Hi
On 3/2/11 11:32 , Ondrej Filip wrote:
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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;
}

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?

			Ondrej
...
/Tias
...
...
Any help is much appreciated.
/Tias