Figure 1 shows the Anycast mechanism used to support gateway redundancy for dual BGP instance services. The example shows two redundant DC gateways (DGWs) where the VPLS services contain two BGP instances: one each for EVPN-VXLAN and EVPN-MPLS.
The example shown in Figure 1 depends on the ability of the two DC GWs to send the same inclusive multicast route to the remote PE or NVEs, such that:
The remote PE or NVEs create a single BUM destination to one of the DC GWs (because the BGP selects only the best route to the DC GWs).
The DC GWs do not create a destination between each other.
This solution avoids loops for BUM traffic, and known unicast traffic can use either DGW router, depending on the BGP selection. The following CLI example output shows the configuration of each DGW.
/* bgp configuration on DCGW1 and DCGW2 */
config>router>bgp#
group ”WAN"
family evpn
type internal
neighbor 192.0.2.6
group ”DC"
family evpn
type internal
neighbor 192.0.2.2
/* vpls service configuration */
DCGW-1# config>service>vpls(1)#
-----------------------
bgp
route-distinguisher 64501:12
route-target target:64500:1
exit
bgp 2
route-distinguisher 64502:12
route-target target:64500:1
exit
vxlan instance 1 vni 1 create
exit
bgp-evpn
evi 1
incl-mcast-orig-ip 10.12.12.12
vxlan bgp 1 vxlan-instance 1
no shutdown
mpls bgp 2
no shutdown
auto-bind-tunnel
resolution any
exit
<snip>
DCGW-2# config>service>vpls(1)#
-----------------------
bgp
route-distinguisher 64501:12
route-target target:64500:1
exit
bgp 2
route-distinguisher 64502:12
route-target target:64500:1
exit
vxlan instance 1 vni 1 create
exit
bgp-evpn
evi 1
incl-mcast-orig-ip 10.12.12.12
vxlan bgp 1 vxlan-instance 1
no shutdown
mpls bgp 2
no shutdown
auto-bind-tunnel
resolution any
<snip>
Based on the preceding configuration example, the DC GWs behavior in this scenario is as follows:
DCGW-1 and DCGW-2 send inclusive multicast routes to the DC RR and WAN RR with the same route key. For example:
DCGW-1 and DCGW-2 both send an IR route to DC RR with RD=64501:12, orig-ip=10.12.12.12, and a different next-hop and tunnel ID
DCGW-1 and DCGW-2 both send an IR route to WAN RR with RD=64502:12, orig-ip=10.12.12.12, and different next-hop and tunnel ID
DCGW-1 and DCGW-2 both receive MAC/IP routes from DC and WAN that are redistributed to the other BGP instances, assuming that the route is selected as best route and the MAC is installed in the FDB
As described in section BGP-EVPN Routes in Services Configured with Two BGP Instances, router peer policies are required so that only VXLAN or MPLS routes are sent or received for a specific peer
Configuration of the same incl-mcast-orig-ip address in both DCGWs enables the Anycast solution for BUM traffic for all the following reasons.
The configured originating-ip is not required to be a reachable IP address and this forces the remote PE or NVEs to select only one of the two DC GWs.
The BGP next-hops are allowed to be the system-ip or even a loopback address. In both cases, the BGP next-hops are not required to be reachable in their respective networks.
In the example shown in Figure 1, PE-1 picks up DC GW-1's inclusive multicast route (because of its lower BGP next-hop) and create a BUM destination to 192.0.2.4. When sending BUM traffic for VPLS-1, it only sends the traffic to DC GW-1. In the same way, the DC GWs do no set up BUM destinations between each other as they use the same originating-ip in their inclusive multicast routes.
The remote PE or NVEs perform a similar BGP selection for MAC or IP routes, as a specific MAC is sent by the two DC GWs with the same route-key. A PE or NVE sends known unicast traffic for a specific MAC to only one DGW.