Allied Telesis AT-S63 - Manual (Page 404)

Chapter 20: RRP Snooping
404 Section III: IGMP Snooping, MLD Snooping, and RRP Snooping
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 need not
necessitate an adjustment to 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 having to manually reconfigure
default gateway addresses on large numbers of network nodes when a
router pathway fails.
RRP snooping on the AT-9400 Series 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 to
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.
The following guidelines apply to the RRP snooping feature:
ˆ The default setting for this feature is disabled.
ˆ Activating the feature flushes all dynamic MAC addresses from the
MAC address table.