Mec Failure Scenarios - Cisco Catalyst 4500 series Administration Manual

Chapter 5 Configuring Virtual Switching Systems
An MEC can support up to eight physical links, which can be distributed in any proportion between the
VSS Active and VSS Standby switch.
Figure 5-7
Virtual switch
Supervisor
engine

MEC Failure Scenarios

We recommend that you configure the MEC with at least one link to each switch. This configuration
conserves VSL bandwidth (traffic egress link is on the same switch as the ingress link), and increases
network reliability (if one VSS supervisor engine fails, the MEC is still operational).
The following sections describe possible failures and the resulting impacts:
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Single MEC Link Failure
If a link within the MEC fails (and other links in the MEC are still operational), the MEC redistributes
the load among the operational links, as in a regular port.
All MEC Links to the VSS Active Switch Fail
If all links to the VSS Active switch fail, the MEC becomes a regular EtherChannel with operational
links to the VSS Standby switch.
Data traffic terminating on the VSS Active switch reaches the MEC by crossing the VSL to the VSS
Standby switch. Control protocols continue to run in the VSS Active switch. Protocol messages reach
the MEC by crossing the VSL.
OL-30933-01
MEC Topology
Router, switch
Active chassis
Single MEC Link Failure, page 5-15
All MEC Links to the VSS Active Switch Fail, page 5-15
All MEC Links to the VSS Standby Switch Fail, page 5-16
All MEC Links Fail, page 5-16
VSS Standby Switch Failure, page 5-16
VSS Active Switch Failure, page 5-16
or server
MEC
Standby chassis
Software Configuration Guide—Release IOS XE 3.6.0E and IOS 15.2(2)SG
Understanding Virtual Switching Systems
Supervisor
engine
5-15