EVPN-MPLS Multi-Homing and Passive VRRP

SAP and spoke SDP based ESs are supported on R-VPLS services where bgp-evpn mpls is enabled.

Figure 1 shows an example of EVPN-MPLS multi-homing in R-VPLS services, with the following assumptions.

Figure 1. EVPN-MPLS Multi-Homing in R-VPLS Services

In the example in Figure 1, the hosts connected to CE1 and CE4 could use regular VRRP for default gateway redundancy; however, this may not be the most efficient way to provide upstream routing.

For example, if PE1 and PE2 are using regular VRRP, the upstream traffic from CE1 may be hashed to the backup IRB VRRP interface, instead of being hashed to the active interface. The same thing may occur for single-active multi-homing and regular VRRP for PE3 and PE4. The traffic from CE4 is sent to PE3, while PE4 may be the active VRRP router. In that case, PE3 has to send the traffic to PE4, instead of route it directly.

In both cases, unnecessary bandwidth between the PEs is used to get to the active IRB interface. In addition, VRRP scaling is limited if aggressive keepalive timers are used.

Because of these issues, passive VRRP is recommended as the best method when EVPN-MPLS multi-homing is used in combination with R-VPLS redundant interfaces.

Passive VRRP is a VRRP setting in which the transmission and reception of keepalive messages is completely suppressed, and therefore the VPRN interface always behaves as the active router. Passive VRRP is enabled by adding the passive keyword to the VRRP instance at creation, as shown in the following examples:

config service vprn 1 interface int-1 vrrp 1 passive

config service vprn 1 interface int-1 ipv6 vrrp 1 passive

For example, if PE1, PE2, and PE5 in Figure 1 use passive VRRP, even if each individual R-VPLS interface has a different MAC/IP address, because they share the same VRRP instance 1 and the same backup IP, the three PEs own the same virtual MAC and virtual IP address (for example, 00-00-5E-00-00-01 and 10.0.0.254). The virtual MAC is auto-derived from 00-00-5E-00-00-VRID per RFC 3768. The following is the expected behavior when passive VRRP is used in this example.

The following list summarizes the advantages of using passive VRRP mode versus regular VRRP for EVPN-MPLS multi-homing in R-VPLS services.