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N5K: PortChannel & Load Balancing

Hello All,

I've configured port-channel for my backup servers and also applied load balancing on the switch (NEXUS 5548 with 2248 FEX). The server is configured with NIC teaming and is set on auto, which negotiates to use 802.3ad for the channel.

All seems to be working fine however the ports do not seem to be balancing the traffic when transmitting unicast traffic as shown from below N5K output:

ChanId      Port     Rx-Ucst  Tx-Ucst  Rx-Mcst     Tx-Mcst   Rx-Bcst  Tx-Bcst

------       ---------       -------     -------        ------- -    ------ -        ------      -------

  20   Eth102/1/6  52.61%  99.99%    49.45%  63.29%  93.55%  51.27%

  20   Eth102/1/5  47.38%   0.00%     50.54%  36.70%   6.44%    48.72%

------       ---------       -------    -------       -------         -------       -------       -------

  21   Eth102/1/33  51.25%  99.99%  49.92%  63.01%   15.51%   51.40%

  21   Eth102/1/29  48.74%  0.00%  50.07%  36.98%     84.48%   48.59%

The above shows the server is receiving traffic only on one port and not balancing it on another. Server is WIn 2008 R2. These are 1 Gig links with PO are 2 Gig, the backup server needs the 2 Gig but somehow it doesnt seem to utilize the port-channel for incoming traffic.

Currently the load balancing on the N5K platform is set as follows:

N5K# show port-channel load-balance

Port Channel Load-Balancing Configuration:
System: source-dest-port

Port Channel Load-Balancing Addresses Used Per-Protocol:
Non-IP: source-dest-mac
IP: source-dest-port source-dest-ip source-dest-mac

My question here is can i load balance the Tx-Ucst to both ports?

Is there some other way I can utilize both NIC cards on the server to receive traffic?

Any help would be much appreciated.

Thank you.


Adnan M F

Community Member

N5K: PortChannel & Load Balancing


You seem to be using the recommended hashing algorithm. I would use the "show port-channel load-balance forwarding-path" command to verify that your traffic would actually load balance. Because you mention these are backup servers, I'm concerned there may not be enough entropy in the packets to load balance as you'd like.

example :

show port-channel load-balance forwarding-path interface port-channel 301 vlan 1 src-ip l4-dst-port 80 dst-ip l4-src-port 20000

Missing params will be substituted by 0's.

Load-balance Algorithm on switch: source-dest-ip

crc8_hash: Not Used     Outgoing port id: Ethernet1/9

Param(s) used to calculate load-balance (Unknown unicast, multicast and broadcas

t packets):

        dst-mac:  0000.0000.0000

        vlan id:  1

If the "show port-channel load-balance forwarding-path" commands shows that your traffic should transmit out eth102/1/5 or eth102/1/29, then it's possible you are having bug issues. There are known bugs that were fixed in 5.2(9) and 6.1(4) that affect load balancing.

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