Router Redundancy Using XRRP
Overview of XRRP Operation
If Communication is Maintained Through Non-XRRP Interfaces. In
some cases, it may be possible that all connectivity is lost between the routers
on all their XRRP virtual router interfaces, in which case XRRP operates and
both routers try to take control of all the virtual routers in the Protection
Domain, but if connectivity still exists on non-XRRP VLANs, a situation could
occur in which both routers allow and use the same MAC addresses on the
non-XRRP VLAN(s). This could create a situation in which a switch connected
between the two routers will see continuous move interrupts and potential
duplication of inbound packets if that switch floods. To prevent this condition,
a simple XRRP protocol packet is exchanged between the two routers on the
non-XRRP VLAN to inform each other of their uses of the MAC addresses. This
exchange prevents the routers from taking over each other’s MAC addresses.
Note that this protocol is used only when one router attempts to take over
control of the other routers virtual router interfaces.
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.
12-9
To Next Page
Loading...
