Different export route target for different prefixes of a same VRF

[Ondrej Zajicek]

On Tue, Jun 13, 2023 at 10:47:08AM +0530, Ramanathan Selvamani wrote:
> Hi Team,
> 
> I configured l3vpn in BIRD and I was able to see the routes are learnt and
> advertised based on RT.
> 
> All the routes in this VRF are advertised with RT (1:11) to neighbors.

Hi

I am glad you tried this MPLS L3VPN branch, i would be interested in
your experiences and suggestions with it.


> I have a use case in which I want to apply different RT for different
> routes belonging to the same VRF.
> 
> For example,
> I have the following prefixes in this VRF "vrf2".
> 101.1.1.0/24
> 103.1.1.0/24
> 105.1.1.0/24
> 
> I would like to add different "export route target" as below for routes
> belong to same VRF
> 101.1.1.0/24 :  export RT 1:11
> 103.1.1.0/24 :  export RT  1:20
> 105.1.1.0/24 :  export RT  1:30

Currently, the implicit export RT processing works by removing all RT
communitines and then adding ones specified in the export target
option.

If you want to set individual route targets, you could just keep the
export target set empty and add individual communities ex-post in vpn4
channel import filter (VRF export direction first passes through ipvX
channel export filter, then internal processing, then vpnX channel import
filter), with something like:

case (net) {
  1:11 101.1.1.0/24: bgp_ext_community.add((rt, 1, 11));
  1:11 103.1.1.0/24: bgp_ext_community.add((rt, 1, 20));
  1:11 105.1.1.0/24: bgp_ext_community.add((rt, 1, 30));
}

(note that in vpnX import filter the route is already converted to VPNv4 NLRI, so 'net'
is RD + prefix.


There is an alternative approach, which is not yet implemented, but there
should be an option with EC set that instead of appriori removing all
existing RTs during export, it should keep a defined subset (say [(rt, 1,
10..40)]), and then these RTs could be passed from original IP routes
from VRF.

-- 
Elen sila lumenn' omentielvo

Ondrej 'Santiago' Zajicek (email: santiago at crfreenet.org)
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"To err is human -- to blame it on a computer is even more so."