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Load Balancing Methods for Port Channels on Nexus

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Introduction

A port channel bundles up to eight individual interfaces into a group to provide increased bandwidth and redundancy. You can also have upto sixteen ports in a port channel in active/standby setup. 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. You can configure and run either static port channels or ports channels running the Link Aggregation Control Protocol (LACP). Cisco NX-OS does not support Port Aggregation Protocol (PAgP) for port channels.

 

LACP

With LACP, you can bundle up to eight interfaces in a channel group. You must enable LACP before the feature functions. Each system that runs LACP has an LACP system priority value. You can accept the default value of 32768 for this parameter, or you can configure a value between 1 and 65535. Each port configured to use LACP has an LACP port priority. You can accept the default value of 32768 for the LACP port priority, or you can configure a value between 1 and 65535. LACP uses the port priority with the port number to form the port identifier.

 

Loadbalancing Methods

Entering the port channel displays following methods for load balancing.

switch(config)# port-channel load-balance ethernet ?
  destination-ip         Destination IP address
  destination-mac        Destination MAC address
  destination-port       Destination TCP/UDP port
  source-dest-ip         Source & Destination IP address (includes l2)
  source-dest-ip-only    Source & Destination IP addresses only
  source-dest-mac        Source & Destination MAC address
  source-dest-port       Source & Destination TCP/UDP port (includes l2 and l3)
  source-dest-port-only  Source & Destination TCP/UDP port only
  source-ip              Source IP address
  source-mac             Source MAC address
  source-port            Source TCP/UDP port

destination-ip :- Uses destination mac and destination IP to calculate the hash.
destination-mac :- Uses destination mac address to calculate the hash.
destination-port :- Uses destination mac, destination IP and destination port number to calculate the hash.
source-dest-ip :- Same as destination-ip but also includes source mac and IP address.
source-dest-ip-only :- Uses only the source and destination IP address for calculating the hash.
source-dest-mac :- Uses only the source and destination mac address for calculating the hash.
source-dest-port :- Same as destination-port but also includes source mac, IP and port number.
source-dest-port-only :- Uses only the source and destination port numbers for calculating the hash.
source-ip :- Same as destination-ip but instead uses source mac and IP address.
source-mac :- Same as destination-mac but instead uses source mac address.
source-port :- Same as destination-port but instead uses source mac, IP and port number.

 

FEX and Port Channel

On the Nexus 5000/6000 platforms, all FEXs will inherit the global hashing algorithm from the parent device.
 
On the Nexus 7000 platform, hashing algorithms can be assigned on a per FEX basis (all load balancing changes must be made from the Admin VDC).

For example:

N7K-A(config)# port-channel load-balance src-dst ip-l4port fex 134
 
Any FEX without a hashing algorithm configured with inherit the global hash. Making changes to the modular/global hash will not alter FEX specific hashing algorithms.

To verify the configuration applied you can use this command

N5K_A# show port-channel load-balance

On the Nexus 7000, the per FEX algorithm can be checked by appending the ‘fex <#>’ to the end of the command in the Admin VDC or the FEX’s respective VDC.

 

Port Channel Modes

There are three modes to configure a Port Channel.

On : All static EtherChannels, that is, that are not running LACP, remain in this mode. If you attempt to change the channel mode to active or passive before enabling LACP, the device returns an error message.

Active : LACP mode that places a port into an active negotiating state, in which the port initiates negotiations with other ports by sending LACP packets.

Passive : LACP mode that places a port into a passive negotiating state, in which the port responds to LACP packets that it receives but does not initiate LACP negotiation.

 

Related Information

vPC Status Down between Nexus 5000 and Directly connected Server
vPC Best Practices for Nexus 7000 and 5000
vPC Failover Scenarios and Troubleshooting Checklist
Load-balancing Algorithm for NX-OS Port Channels

Comments
Cisco Employee

Hi

the described loadbalancing methods above only apply to unicast, right ?

grtz

Thijs

Cisco Employee
How do these load-balancing algorithums affect FC and FCoE load-balancing? There should be some mention of that in this document. Thanks, Ed Mazurek
Cisco Employee

bump

Beginner

I would also like to know what Thijs asked.  Does the load balancing algorithm only affect unicast traffic or does it also affect mcast/bcast?