Port Channel Compatibility Requirements
When you add an interface to a channel group, the NX-OS software checks certain interface and operational attributes to ensure that the interface is compatible with the channel group. If you configure a member port with an incompatible attribute, the software suspends that port in the port channel. You can use the show port-channel compatibility-parameters command to see the full list of compatibility checks that Cisco NX-OS uses. You can force ports with incompatible parameters to join the port channel if the following parameters are the same:
- (Link) Speed capability and speed configuration
- Duplex capability and duplex configuration
- Flow-control capability and flow-control configuration
When the interface joins a port channel, some of its individual parameters are removed and replaced with the values on the port channel. The following list provides some of these individual parameters:
- Bandwidth
- Delay
- VRF
- IP address
- MAC address
- Spanning Tree Protocol (STP)
- Service policy
- Access control lists (ACLs)
All the QoS service policies on the port channel are implicitly applied on the member ports when they join the port channel. You will not see QoS service policies in the
running-config of the member ports. When you delete the port channel, the software
sets all member interfaces as if they were removed from the port channel.
Many interface parameters remain unaffected when the interface joins or leaves a port channel, including those in the following list:
- Description
- CDP
- LACP port priority
- UDLD
- Rate mode
- Shutdown
- SNMP trap
Each port that is configured to use LACP has an LACP port priority. LACP uses the port priority to decide which ports should be put in standby mode when there is a limitation that prevents all compatible ports from aggregating and which ports should be put into active mode. You can accept the default value of 32768 for the LACP port priority, or you can configure a value between 1 and 65535. A higher port priority value means a lower priority for LACP. You can configure the port priority so that specified ports have a lower priority for LACP and are most likely to be chosen as active links rather than as hot-standby links.
Port Channel Load Balancing
Because a port channel uses several links to transport packets through physical infrastructure, the packets must be distributed between the physical links through some
load-balancing algorithm. The Cisco NX-OS software load-balances traffic across all operational interfaces in a port channel by hashing the addresses in the frame to a numerical value that selects one of the links in the channel.
You can configure the load-balancing mode to apply to all port channels that are configured on the entire device or on specified modules. The per-module configuration takes precedence over the load-balancing configuration for the entire device. You cannot configure the load-balancing method per port channel. The default load-balancing method for Layer 2 packets is src-dst-mac. The default method for Layer 3 packets is src-dst ip-l4port.
You can configure the device to use one of the following methods to load-balance across the port channel:
- Destination MAC address
- Source MAC address
- Source and destination MAC address
- Destination IP address
- Source IP address
- Source and destination IP address
- Source TCP/UDP port number
- Destination TCP/UDP port number
- Source and destination TCP/UDP port number
- GRE inner IP headers with source, destination, and source-destination