Inter-AS Option B and VPN-NH-RR support the use of non-segmented trees for forwarding BUM traffic in EVPN.
For ingress replication and non-segmented trees, the ASBR or ABR performs an EVPN BUM label swap without any aggregation or further replication. This concept is shown in Figure: VPN-NH-RR and ingress replication for BUM traffic.
In Figure: VPN-NH-RR and ingress replication for BUM traffic, when PE2, PE3, and PE4 advertise their IMET routes, the ABRs re-advertise the routes with NHS and a different label. However, IMET routes are not aggregated; therefore, PE1 sets up three different EVPN multicast destinations and sends three copies of every BUM packet, even if they are sent to the same ABR. This example is also applicable to ASBRs and Inter-AS Option B.
P2MP mLDP may also be used with VPN-NH-RR, but not with Inter-AS Option B. The ABRs, however, do not aggregate or change the mLDP root IP addresses in the IMET routes. The root IP addresses must be leaked across IGP domains. For example, if PE2 advertises an IMET route with mLDP or composite tunnel type, PE1 is able to join the mLDP tree if the root IP is leaked into PE1’s IGP domain.