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

[Ondrej Filip]

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;
}

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
>>