Take Specific Value Inside BGP Community

[Erin Shepherd]

It's a bit non-obvious, but you can do this with a loop. For example we basically replicate the Euro-IX routeserver announcement control communities inside our network, and we use the following function to translate them when exporting routes to a (supporting) route server

# Translate Euro-IX common communities for use by a route server
function translate_routeserver_communities(
  int dest_asn
)
{
  lclist announce_controls = filter(bgp_large_community, [(OURAS, 0..1, *)]);
  for lc c in announce_controls do {
    bgp_large_community.add((dest_asn, c.data1, c.data2));
  }

  lclist prepends = filter(bgp_large_community, [(OURAS, 101..103, *)]);
  for lc c in prepends do {
    bgp_large_community.add((dest_asn, c.data1, c.data2));
  }
}

(I think we could combine those into one with a filter(bgp_large_community, [(OURAS, 0..1, *), (OURAS, 101..103, *)])? This code originally looked slightly different and at the time combining these wasn't posible.

Note that this doesn't strip the input communities - we do that as a separate step later where we strip all non-informational communities

- Erin

On Tue, 20 Feb 2024, at 00:30, Ilham Maulana wrote:
> Hi,
> 
> 
> Is it possible in bird to copy specific value inside BGP Community?
> 
> Example:
> 
> Route 1, Community (a,b,*c*) -> inbound
> Route 2, Community (a,b,*d*) -> inbound
> --
> Route 1, Community (k,l,*c*) -> outbound
> Route 2, Community (k,l,*d*) -> outbound
> 
> The specific value I want to preserve is c and d, and it is dynamic variable.
> 
> whatever c and d inbound, copy to c and d outbound.
> 
> Thanks.
> Ilham
> 5f622eb5-c189-4e05-8584-e4a1d2071a6b
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