Support accept-own for the l2vpn evpn address family

[cwmos]

With #12364, route leaking between VNIs in an EVPN-VXLAN setup becomes much more flexible.

For example, to allow one L3 VNI 20 to reach another L3 VNI 10, you can simply configure a route reflector to add a route target for VNI 20 on all routes with a route target for VNI 10.

Overall this works fine - see the FRR configuration below.

However, it a host has a VRF for both VNI 20 and VNI 10, then the local routes to VNI 10 will not be leaked to VNI 20 on that host. The reason is that when the host receives an updated route from the route reflector, it will just discard it since the host created that route originally.

I believe the way to fix this is to use the accept-own mechanism described in https://datatracker.ietf.org/doc/rfc7611/

FRR does support accept-own, but as far as I can see only for the ipv4 vpn address family. So it would be great if accept-own was also supported for the l2vpn evpn address family to allow the described use case.

I understand that the route leak could be configured locally on the host. However, it would be nice if only the route reflector had to be touched when route leaking changes.

To illustrate the example, here is an FRR configuration of the route reflector:

hostname host254

router bgp 65000
  bgp router-id 192.168.1.254
  bgp cluster-id 192.168.1.254
  bgp log-neighbor-changes
  no bgp default ipv4-unicast
  neighbor hosts peer-group
  neighbor hosts remote-as 65000
  neighbor hosts capability extended-nexthop
  neighbor hosts update-source 192.168.1.254
  bgp listen range 192.168.1.0/24 peer-group hosts
  !
  address-family l2vpn evpn
   neighbor hosts activate
   neighbor hosts route-reflector-client
   neighbor hosts route-map VRF_LEAK in
  exit-address-family
  !
!

bgp extcommunity-list standard VRF10 permit rt 65000:10
route-map VRF_LEAK permit 10
  match extcommunity VRF10
  set extcommunity rt 65000:20
  set community accept-own
route-map VRF_LEAK permit 20

And here is a configuration of a host:

hostname host1

vrf vrf10
  vni 10
  exit-vrf
!
vrf vrf20
  vni 20
  exit-vrf
!

router bgp 65000
  bgp router-id 192.168.1.1
  no bgp default ipv4-unicast
  neighbor routereflector peer-group
  neighbor routereflector remote-as 65000
  neighbor routereflector capability extended-nexthop

  ! BGP sessions with route reflectors
  neighbor 192.168.1.254 peer-group routereflector
  !
  address-family l2vpn evpn
   neighbor routereflector activate
   advertise-all-vni

   neighbor routereflector accept-own ! NOT SUPPORTED TODAY
  exit-address-family
!

router bgp 65000 vrf vrf10
  bgp router-id 192.168.1.1
  !
  address-family ipv4 unicast
    redistribute static
    redistribute connected
    redistribute kernel
  exit-address-family
  !
  address-family l2vpn evpn
    advertise ipv4 unicast
  exit-address-family
!

router bgp 65000 vrf vrf20
  bgp router-id 192.168.1.1
  !
  address-family ipv4 unicast
    redistribute static
    redistribute connected
    redistribute kernel
  exit-address-family
  !
  address-family l2vpn evpn
    advertise ipv4 unicast
  exit-address-family
!