Intel 480T, Руководство пользователя

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C H A P T E R 9 Enterprise Standby Router Protocol
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Master Switch Behavior
If a switch is master, it actively provides layer 3 routing services to
other VLANs, and layer 2 switching between all the ports of that
VLAN. Additionally, the switch exchanges ESRP packets with
other switches that are in standby mode.
Standby Switch Behavior
If a switch is in standby mode, it exchanges ESRP packets with
other switches on that same VLAN. When a switch is in standby, it
does not perform layer 3 routing or layer 2 switching services for
the VLAN. From a layer 3 routing protocol perspective (for
example, RIP or OSPF), when in standby for the VLAN, the switch
marks the router interface associated with the VLAN as down. From
a layer 2 switching perspective, no forwarding occurs between the
member ports of the VLAN; this prevents loops and maintains
redundancy.
Electing the Master Switch
A new master can be elected in one of the following ways:
• A communicated parameter change
• Loss of communication between master and slave(s).
If a parameter that determines the master changes (for example, link
loss or priority change), the election of the new master typically
occurs within one timer cycle (2 seconds by default). If a switch in
standby mode loses its connection with the master, a new election
(using the same precedence order indicated previously) occurs.
The new election typically takes place in three times the defined
timer cycle (6 seconds by default).
Failover Time
Failover time is largely determined by the following factors:
• The ESRP timer setting.
• The routing protocol being used for inter-router connectivity if
layer 3 redundancy is used. OSPF fail-over time is faster than RIP
fail-over time.