Cisco Catalyst 6500 User Manual page 7

MultiChassis EtherChannel
A MultiChassis EtherChannel is an EtherChannel with ports that terminate on both chassis of the VSS. A VSS
MEC can connect to any network element that supports EtherChannel, such as a host, server, router, or switch.
At the VSS, an MEC is an EtherChannel with additional capability. The VSS balances the load across ports in
each chassis independently. For example, if traffic enters the active chassis, the VSS selects an MEC link
from the active chassis. This MEC capability ensures that data traffic does not unnecessarily traverse the VSL.
•
L2 MEC enables loop free topology, doubles the uplink bandwidth as no links are blocked and
provides faster convergence than STP.
•
L3 MEC provides reduced neighbor counts, better load−sharing (L2 and L3 for unicast and
multicast), reduced VSL link utilization for multicast flows and faster convergence than ECMP.
Refer to Multichassis EtherChannels for more information on MEC.
Recommendations
•
Always run L2 or L3 MEC.
•
Do not use on and off options with PAgP or LACP or Trunk protocol negotiation.
♦
PAgP †Run Desirable−Desirable with MEC links.
♦
LACP †Run Active−Active with MEC links.
♦
Trunk †Run Desirable−Desirable with MEC links.