Port Channel Configuration

A port-channel or channel group, is an aggregation of multiple physical interfaces that creates a logical interface. A port-channel bundles up to four individual interfaces into a group to provide increased bandwidth and redundancy. Port-channeling also load balances traffic across these physical interfaces. The port-channel stays operational as long as at least one physical interface within the port-channel is operational.

Cisco Nexus 3550-T Programmable Switch Platform allows users to configure up to 12 port-channels. A port-channel can be created by bundling compatible interfaces. A port-channel can be configured to work as a Layer 2 port-channel or a Layer 3 port-channel. Based on the configuration mode of port-channel, it can allow configuring the respective properties like a Layer 2 port-channel can be configured as an access port or as a trunk port. Same way if a port-channel is configured as a Layer 3 port it allows assigning of IP Address and also allows configurations like NAT/ACL to be applied to it. The configuration applied to the port-channel is also applicable for the member interfaces.

Create Port Channel

The Nexus 3550-T enables users to create port-channels by using the CLI.

To create a port-channel, use the following command:

admin@NX-3550-T# configure interface port-channel1 load-balance src-dst-mac

The above command creates a port-channel with id 1. This port-channel will be using the source and destination mac addresses for distributing the traffic across the member interfaces of the port-channel.

Load Balancing in Port Channel

The Nexus 3550-T load balances traffic across all operational interfaces in a port-channel by reducing part of the binary pattern formed from the addresses in the frame to a numerical value that selects one of the links in the channel. Port-channels provide load balancing using symmetric hashing over the Layer 2 or Layer 3 fields in the frame. The load balancing algorithm can be selected at the time of port-channel creation. It can be changed later from CLI by specifying the desired algorithm.

To configure the load balancing algorithm the following command is used:

admin@NX-3550-T# configure interface port-channel1
admin@NX-3550-T(config-if-po1)# load-balance src-dst-ip

Modes of Operation in Port Channel

Port channel can be configured to work in static mode or Link Aggregation Control Protocol (LACP) mode also known as dynamic or 802.3ad mode. The mode can be specified using the CLI. By default, the port-channels operate in static mode.

To configure the LACP mode for a port-channel, use the following command:

admin@NX-3550-T# configure interface port-channel1 lacp

Adding Members to Port Channel

The Nexus 3550-T currently allows up to four physical interfaces to be part of a port-channel. These physical interfaces need to be part of the same quad to be added as a member of the port-channel. So the interfaces ethernet1 to ethernet4 can ONLY be added as a member to port-channel 1. On similar lines interfaces, ethernet5 to ethernet8 can be added as a member of port-channel 2 and so on allowing ethernet45 to ethernet48 to be members of port-channel 12. An interface can be added as a member of port-channel using the following command:

admin@NX-3550-T(config)# int et2 channel-group 1

The above command will add an interface ethernet2 to port-channel 1. In case the port-channel was not created prior to running this command, it will also create a new port-channel with the default configuration.

In case multiple interfaces are to be added as members of a port-channel, the following command can be used.

admin@NX-3550-T(config)# int et1-3 channel-group 1

The above command will add interfaces ethernet1 to ethernet4 as members of the port-channel 1. If an invalid interface and port-channel combination is supplied as part of the command, an error highlighting that the combination is invalid gets printed on the CLI.

admin@NX-3550-T(config)# int et5-7 channel-group 1
ethernet5 cannot be a member of port-channel1
ethernet6 cannot be a member of port-channel1
ethernet7 cannot be a member of port-channel1

To dump all the configured port-channel use the following command:

admin@NX-3550-T(config)# show port-channel
port-channel Mode   Ports
------------ ------ -------------------------------
1            static ethernet1; ethernet2; ethernet3

Port Channel as Layer2 Interface

Port channel can be configured to work as a Layer2 interface working in access mode or trunk mode via CLI using the following command:

admin@NX-3550-T# configure interface port-channel1
admin@NX-3550-T(config-if-po1)# switchport mode access

Once the port-channel is configured in access mode, CLI can be used to configure the VLAN for the port-channel. If no VLAN configuration is applied to the port-channel, it will become a member of VLAN 1.

admin@NX-3550-T(config-if-po1)# switchport access vlan 10

Port Channel as Layer3 Interface

Port channel can be configured to work as a Layer3 interface via CLI using the following command:

admin@NX-3550-T# configure interface port-channel1
admin@NX-3550-T(config-if-po1)# ip address 10.0.0.1/24

Once the port-channel is configured to work as a Layer3 interface, all the layer3 features like NAT/ACL can be applied to the port-channel. For example below commands configure port-channel 1 as a NAT interface. For all other commands please refer to the respective sections.

admin@NX-3550-T(config-if-po1)# ip nat inside

This page was last updated on Mar-23-2021.