Cisco Catalyst 6880-X Specifications download pdf (Page 92)

Core Layer April 2014

The VSL allows the switches to communicate and stay in synchronization. The VSS uses the Stateful Switchover

(SSO) redundancy facility to keep the control plane synchronized between the two switches. As a result, the VSS

appears to devices in adjoining layers as a single switch with a single MAC address.

Step 6: Configure dual-active detection mechanism.

In the event that the VSL is severed (that is, all links are down), or for any reason communication is lost over

the VSL (such as excessive high CPU utilization), both supervisors would assume the active control plane role,

thus creating a dual-active condition, that can result in network instability. To prevent a dual-active scenario

from causing an outage in the network, VSS supports multiple unique dual-active detection and recovery

mechanisms.

The dual-active detection mechanisms are used to trigger a VSS recovery mode. In the VSS recovery mode

only one switch chassis is allowed to remain active, the other switch (the previous VSS active switch) enters

recovery mode, and shuts down all of its interfaces except the VSL interfaces, thereby preventing instability in

the network. Once the VSL is repaired, and communication over the VSL is reestablished, then the VSS reloads

the switch in recovery mode and returns the VSS to a normal operating state.

You can use the following methods to detect this dual-active condition:

• Virtual Switch Link Protocol (VSLP) Ethernet Fast-Hello link

• Enhanced Port Aggregation Protocol (PAgP) hellos with an adjacent switch

This design uses the Fast-Hello (VSLP) link for dual-active detection. Configure the link by using a Gigabit

Ethernet interface on each VSS switch chassis and cabling them together (similar to a VSL connection) in a

back-to-back fashion. This link does not require high bandwidth because it is only a detection link with control

plane hellos on it.

Figure 28 - VSLP

VSL 10GbE

EtherChannel

VSLP Dual-Active

Detect Link

Active Hot

Standby

2108

C6500-VSS(config)# switch virtual domain 101

C6500-VSS(config-vs-domain)#dual-active detection fast-hello

C6500-VSS(config)#interface range gigabit1/1/24, gigabit2/1/24

C6500-VSS(config-if-range)#dual-active fast-hello

C6500-VSS(config-if-range)#no shutdown

%VSDA-SW1-5-LINK_UP: Interface Gi1/1/24 is now dual-active detection capable

%VSDA-SW2_STBY-5-LINK_UP: Interface Gi2/1/24 is now dual-active detection capable

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Cisco Catalyst 6880-X Specifications Page 92