Cisco Cisco 1700 2600 3600 3700 Series VPN Module White Paper

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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.