Cisco Cisco 1700 2600 3600 3700 Series VPN Module White Paper
© 2012 Cisco and/or its affiliates. All rights reserved. This document is Cisco Public Information.
Page 19 of 55
4 Po4(SU) PAgP Gi1/5/3(P) Gi2/5/3(P)
Last applied Hash Distribution Algorithm: Adaptive
Although this new load-distribution algorithm requires configuration for regular Cisco EtherChannel and
multichassis Cisco EtherChannel interfaces, it is the default load-distribution algorithm used on the virtual switch
links.
Multichassis Cisco EtherChannel Links
The multichassis Cisco EtherChannel interface spans more than a single physical switch (Figure 11). The Cisco
Virtual Switching System allows the formation of this multichassis Cisco EtherChannel link. It also allows the dual-
homed connections to and from the upstream and downstream devices to be configured as Cisco EtherChannel
links, as opposed to individual links. As a result, multichassis Cisco EtherChannel links allow for implementation of
new network designs where true Layer 2 multipathing can be implemented, without the reliance on Layer 2
redundancy protocols such as Spanning Tree Protocol. With 12.2(33)SXI and above, VSS supports 512
EtherChannels.
Figure 10. Multichassis Cisco EtherChannel Links
Like regular Cisco EtherChannel interfaces, all ports within the multichassis Cisco EtherChannel link have the
same source index, regardless of the chassis in which they are physically present. This makes it possible to apply
a single IP address for Layer 3 Cisco EtherChannel links or for Spanning Tree Protocol to view a Cisco
EtherChannel interface as a single, logical port.
One unique difference between multichassis Cisco EtherChannel and regular Cisco EtherChannel interfaces is the
way traffic is load-balanced across the channel group members. A regular Cisco EtherChannel link selects the
appropriate channel group member to exit, based purely on the hashing algorithm of choice. A multichassis Cisco
EtherChannel link, however, has some extra intelligence to reduce the amount of traffic that requires transmission
across the VSL. This optimization is accomplished by populating the index port only with the ports local to the
physical chassis. This allows the chassis to favor the local ports of the multichassis Cisco EtherChannel link over
those on the remote chassis.