Datalink Layer

Traffic that flows across a port-channel is not forwarded out member links in a round robin basis. A hash is calculated and packets are consistently forwarded across a link based on that calculated hash. The load balancing hash is a system wide configuration that uses a global command: port-channel load-balance X where X is the…

With the port channel being a logic interface, problems can occur if the physical member interfaces are not configured similarly. Generally each member state must all be in either in a layer 2 or layer 3 port type, then associated with the port channel. The rest of the configuration should be done from the logical…

LACP interface priority enables the master switch to choose which member interfaces are active in a port channel when there are more member interfaces than the maximum permitted. A port with a lower priority number is preferred. The interface priority can be set in interface configuration mode, with the command lacp port-priority 1

The LACP system priority identifies the master switch for a port channel. The master switch is responsible for choosing the interfaces that are active in a port channel, and if there are more than the maximum number configured which interfaces are disabled. The system with the lower system priority is preferred. The system priority can…

An etherchannel can be configured to have a specific maximum number of interfaces. A scenario where this can be useful is ensure the active member count is within the powers of two. (2 links, 4 links, 8 links) for load balancing algorithm purposes. To set the maximum number of member interfaces in a port-channel, configure…

An etherchannel typically comes online when only one member interface can successfully form an adjacency with a remote device. In some network design scenarios there may be a situation where a single member interface won’t provide enough bandwidth to serve traffic effectively. A minimum number of member interfaces to be established can be set in…

The original LCP standards sent out a LACP protocol packet every 30 seconds; if a LACP packet is not received three times then the link is deemed unusable. This may result in up to a 90 second delay before a problematic link is removed from the port channel. An amendment was made to the standards…

show etherchannel port show etherchannel port can display detailed information on the local configuration and information from the packets received. This in some cases can provide too much information and slow down the network administrators troubleshooting efforts. Commands exist to be more specific in troubleshooting efforts. show lacp neighbor show lacp neighbor with the optional…

Once a port channel has established, it is important to check that it is operating optimally. The command show etherchannel summary provides a summary of configured port channels on the switch along with its status. Status Code Description U The Etherchannel is up and working correctly D The Etherchannel is down and not working M…

Etherchannel is configured in the interface configuration mode of the switch. There are three ways that it can be configured: statically, LACP, or PAgP. X in the examples below are the channel-group number. Statically channel-group X mode on LACP Etherchannel Active Mode channel-group X mode active Passive Mode channel-group X mode passive PAgP Etherchannel Desirable…