Cisco Cisco Nexus 5010 Switch Guida Alla Progettazione
Design Guide
© 2010 Cisco and/or its affiliates. All rights reserved. This document is Cisco Public Information.
Page 9 of 38
Figure 6. Traffic Flows with vPC
Dual-Control Plane with Single Layer 2 Node Behavior
While still operating with two separate control planes, vPC helps ensure that the neighboring devices connected in
vPC mode see the vPC peers as a single spanning-tree and LACP entity. For this to happen, the system has to
perform IEEE 802.3ad control-plane operations in a slightly modified way (which is not noticeable to the neighbor
switch).
Link Aggregation Group Identifier
IEEE 802.3ad specifies the standard implementation of PortChannels. PortChannel specifications provide LACP as a
standard protocol, which enables negotiation of port bundling.
LACP makes misconfiguration less likely, because if ports are mismatched, they will not form a PortChannel.
Consider example A in Figure 8, in which switch 1 connects to switch 2. Port 1 on switch 1 connects to port 4 on
switch 2, and port 2 on switch 1 connects to port 6 on switch 2.
Now imagine that the administrator configured a PortChannel on switch 1 between ports 1 and 2, while on switch 2
the PortChannel is configured between ports 5 and 3. Without LACP, the ports could be configured in channel-group
mode, and you would not discover that this is a misconfiguration until you notice that traffic has dropped.