Nortel Web OS 10.0, Application Manual

Page: 257 / 482

Web OS 10.0 Application Guide
Chapter 11: High Availability
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212777-A, February 2002
Virtual Router Group
The virtual router group ties all of the virtual routers together as a single entity and is central to
the hot-standby configuration. All virtual routers on a given switch must all be either master or
backup. They cannot failover individually, only as a group. Once hot-standby is globally
enabled, the virtual router group must be enabled. The virtual router group aggregates all of the
virtual routers as a single entity.
If the virtual router group is master on one switch, it means the switch is master; otherwise, the
switch is backup. However, Layer 4 processing is still enabled. If a virtual server is not a vir-
tual router, the backup switch can still process traffic addressed to that virtual server IP
address. Filtering is also still functional. Only traffic addressed to virtual server routers is not
processed.
VRRP actually contains support for virtual router groups. Each advertisement is not limited to
a single virtual router IP address and can include up to 256 addresses. This means that all vir-
tual routers are advertised in the same packet, conserving processing and buffering resources.
However, the advertisements are also used to help bridges learn the virtual router MAC
address. Since all of the virtual routers can have different virtual router identifiers (VRIDs),
you must rotate the MAC source address of the advertisement to ensure that the bridges learn
all of the virtual router MAC addresses.
Hot-Standby and Inter-Switch Port States
The second part of the solution involves introducing two additional Layer 4 port states, hot-
standby and inter-switch:
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Links that attach to the standby switch must be configured as hot standby using
/cfg/slb/port x/hotstan
.
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Links that are used by VRRP to deliver updates are configured as
intersw
, or inter-
switch links (not to be confused with Cisco’s ISL). The command to configure one or
more ports as interswitch links is
/cfg/slb/port <port number> /intersw .
N
OTE
– A port cannot be configured to support both hot-standby and interswitch link.
The hot-standby switch listens to the master’s VRRP updates. After an interval period has
expired without receiving a update, the backup switch will take over. The forwarding states of
hot-standby ports are controlled much like the forwarding states of the old hot-standby
approach. Enabling hot-standby on a switch port allows the hot-standby algorithm to control
the forwarding state of the port. If a switch is master, the forwarding states of the hot-standby
ports are enabled. If a switch is backup, the hot-standby ports are blocked from forwarding or
receiving traffic.