Product guide

Router Redundancy Using XRRP
Overview of XRRP Operation
XRRP Operating Notes
■ Reserved Multicast MAC Address – XRRP uses the following multicast
MAC address for its protocol packets: 0101-E794-0640
■ Use of Proxy ARP on non-XRRP VLANs – Although it is not disallowed,
you should not configure Proxy ARP on non-XRRP VLANs on a router
running XRRP. To do so will potentially cause loss connectivity on those
non-XRRP VLANs should the router fail-over to the other router in the
Protection Domain.
The non-XRRP VLANs will not fail-over, however the XRRP-assigned MAC
address, which were used while the router was operating as an XRRP
router, were used on all the router interfaces, XRRP and non-XRRP. When
the router fails-over its XRRP interfaces, it stops operating as an XRRP
router and reverts back to using the default factory-assigned MAC address
on all the interfaces. Any hosts that rely on proxy ARP will only receive
updated ARPs for the router MAC address not for all the possible IP
addresses that the router had previously responded too as a proxy ARP
interface. Note: this is not a problem on the XRRP interfaces because the
XRRP-assigned MAC address will have moved over to the other router and
proxy ARP learned routes will still be valid. (See also “Router connec-
tivity” on the next page).
■ Static and Default route usage – You should never set up a default or
static route that points to the peer XRRP router as the path. Should fail-
over occur, this path is no longer valid and connectivity on that path will
be lost.
■ Router connectivity – In general peer routers using XRRP must have
identical connectivity. That is, they must have the same access to all
remote subnets, and the route costs of the access must be the same. This
will prevent the routing protocols from using the peer XRRP router as the
best path to get to a given subnet.
If this is not done, then fail-over may have to wait until the routing
protocols converge before full connectivity is restored. Should one router
have exclusive access to a given subnet, (that is, the only way one of the
XRRP routers can get to a given subnet is though its peer) connectivity to
those exclusive subnets may be lost when fail-over occurs.
■ SNMP Requests – SNMP requests on an XRRP router interface follow
the virtual interface, which may be different from the physical interface
in a fail-over situation. Alternately, you can ensure that the SNMP requests
are made on the management VLAN or other non-XRRP interface.
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