Allied Telesis AT-S63 - Manual (Page 364)

Chapter 19: RRP Snooping
364 Section II: Advanced Operations
RRP Snooping Overview
The Router Redundancy Protocol (RRP) allows multiple routers to share
the same virtual IP address and MAC address. In network topologies
where redundant router paths or links exist, the protocol enables routers,
through an election process, to designate one as the master router. This
router functions as the provider of the primary path between LAN
segments. Slave routers function as backup paths in the event that the
master router or primary path fails.
Because the master and slave routers are able to share the same virtual
IP address and MAC address, a change in data paths does not
necessitate adjusting the default gateways on the network nodes that
employ the routers. When a slave router transitions to master, it uses the
same IP address as the previous master router, making the transition
transparent to network end nodes. In large networks, these transparent
transitions can save the time and effort of manually reconfiguring default
gateway addresses on large numbers of network nodes when a router
pathway fails.
RRP snooping on the switch facilitates the transition to a new master
router by minimizing the loss of traffic, and so reduces the impact the
transition could have on your network traffic. RRP snooping monitors
ingress RRP packets, determined by their source MAC address. Source
MAC addresses considered by the AT-S63 management software as RRP
packets are:
ˆ 00:E0:2B:00:00:80-9F
ˆ 00:A0:D2EB:FF:00
ˆ 00:00:5E:00:01:00-FF
A port receiving an RRP packet is deemed by the switch as the master
RRP port. The virtual MAC address of the router is entered as a dynamic
address on the port. If the switch starts to receive RRP packets on another
port, it assumes that a backup or slave router has made the transition into
the role of the new master router.
The switch responds by deleting all dynamic MAC addresses from the
MAC address table. As the switch relearns the addresses, the virtual MAC
address of the new master router is learned on the new master RRP port,
rather than the old port. Any packets received by the switch and destined
for the router are forwarded to the new master router.