Cisco Cisco 1700 2600 3600 3700 Series VPN Module 白皮書
© 2012 Cisco and/or its affiliates. All rights reserved. This document is Cisco Public Information.
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Figure 19. Virtual Switch Preemption
You should enable Switch Preemption only on the switch that has the higher switch priority. With the following
command, you can enable this function under the virtual switch configuration mode. You can specify an optional
timer value from 5 to 20 minutes, where this number represents the number of minutes the current active virtual
switch waits after it establishes communication with the peer standby virtual switch through the VSL. The default
and minimum time is set to 5 minutes. This timer is important, because it takes a variable amount of time after VSL
initialization to initialize the remaining modules and establish network connectivity.
vss#conf t
Enter configuration commands, one per line. End with CNTL/Z.
vss(config)#switch virtual domain 10
vss(config-vs-domain)#switch 2 preempt 7
vss(config-vs-domain)#^Z
vss#
Use the following command to verify the configuration:
vss#show switch virtual role
Switch Switch Status Preempt Priority Role Session ID
Number Oper(Conf) Oper(Conf) Local Remote
------------------------------------------------------------------
LOCAL 1 UP FALSE(N) 100(100) ACTIVE 0 0
REMOTE 2 UP TRUE (Y*) 120(120) STANDBY 1170 1366
Standby operational preempt timer(switch 2): 7 minutes
Standby will takeover as active in approx. : 4 minutes
Standby configured preempt timer(switch 2): 7 minutes
In dual-active recovery mode: No
Preemption should only be configured if there is a compelling requirement to do so. If preemption is enabled, the
convergence time will be longer due to the fact that the switch will experience an additional reload. This additional
reload is necessary, in order for the new switch to go from an active to a standby state.
First Hop Redundancy Protocols
First Hop Redundancy Protocols (Hot Standby Router Protocol [HSRP], Gateway Load Balancing Protocol [GLBP],
and Virtual Router Redundancy Protocol [VRRP]) provide default gateway redundancy for devices when there are
two or more redundant routing nodes, but the attached devices are not learning the network topology through
Layer 3 routing protocols.