Router Redundancy Using XRRP
Overview of XRRP Operation
Note Figure 12-3 shows a single interface on VLAN 5, but multiple interfaces could
exist. For the fail-over to occur, Router-2 must have lost communication on
all the VLAN 5 interfaces.
When the fail-over occurs, Router-1 would take over as the Master of the IP
address for Router-2 on VLAN 5. If Router-2 has multiple IP addresses on VLAN
5, a multinet situation, Router-1 takes over all the IP addresses for Router-2
on VLAN 5.
Multiple VLAN Operation
If a router has XRRP interfaces in multiple VLANs, there are some additional
details in the way that XRRP operates. For each VLAN on which you wish to
run XRRP, a virtual router interface is created.
Total Router Fail-Over. In the multiple VLAN case, fail-over again occurs
when XRRP packets are not heard on at least one of the VLANs from the other
virtual router in the Protection Domain. Even if one or more VLANs are still
operating correctly, when one VLAN fails (a link signal is no longer detected
by the router from any device in the VLAN), the router with the failed VLAN
will stop its operation as the Master of its owned virtual router interfaces. The
fail over is a “total router” fail over. The router with the failed VLAN stops
routing on all of its XRRP virtual interfaces and the other router in the
Protection Domain takes control of all the XRRP IP and MAC addresses.
Depending on whether the routers can maintain communication through at
least one or the XRRP VLANs (the VLAN continues to operate correctly for
both routers in the Protection Domain), the type of fail-over varies:
■ If communication is maintained, the router with the failed VLAN can
execute what is called a “fast fail-over”. This situation is depicted in figure
12-4.
■ If all XRRP communication is lost between the routers in the Protection
Domain, the normal fail-over occurs after 3 advertisement intervals, as
shown in
figure 12-5.
12-6
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