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shrikantupadhyay
Beginner

Nexus 5000 port-channel load-balance hash algorithm based on type of frame

According to the Cisco Nexus 5000 Series NX-OS Software Configuration Guide - 

 

Port channels provide load balancing by default and the basic configuration uses the following criteria to select the link:

- For a Layer 2 frame, it uses the source and destination MAC addresses.
- For a Layer 3 frame, it uses the source and destination MAC addresses and the source and destination IP addresses.
- For a Layer 4 frame, it uses the source and destination MAC addresses, the source and destination IP addresses, and the source and destination port number.

 

My question is, how is the frame determined/classified as layer 2, 3 or 4? Or is it determined based on the configured load-balancing algorithm - src-dst-mac, src-dst-ip, src-dst-port?

2 REPLIES 2
ADP_89
Beginner

Hello,

 

The frame type is determined by the Forwarding Engine based on an in-line lookup on the frame self. The FE has full visibility about all the header bits(payload as well but it's not relevant) so it can perform a logic computation to determine what kind of traffic that frame is transporting.

Based on this result it will apply the chosen hashing algorithm.

 

HTH,

ADP

sbhadrav@cisco.com
Contributor

Cisco NX-OS 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 by default.

The basic configuration uses the following criteria to select the link:
For a Layer 2 frame, it uses the source and destination MAC addresses.
For a Layer 3 frame, it uses the source and destination MAC addresses and the source and destination IP addresses.
For a Layer 4 frame, it uses the source and destination MAC addresses and the source and destination IP addresses.
You have the option to include the source and destination port number for the Layer 4 frame.
For more details please refer the link below:-
https://www.cisco.com/c/en/us/td/docs/switches/datacenter/nexus5000/sw/interfaces/521_N11/b_5k_Interfaces_Config_Guide_Release_521N11/b_5k_Interfaces_Config_Guide_Release_521N11_chapter_0100.html