[c-nsp] Issue with port-channel hashing

james list jameslist72 at gmail.com
Sun Jul 24 01:46:18 EDT 2016

Hi Matt
where can I find the exact alghorithm for the load balancing decision ?

I see two host on the same subnet (Storage replication) are using the same

I read that the command "port-channel load-balance src-dst-mixed-ip-port"
could cause from secs to mins of traffic loss... I cannot try it :-(


2016-07-23 0:53 GMT+02:00 Mack McBride <mack.mcbride at viawest.com>:

> With some traffic patterns there isn't much you can do.
> If there are very few source and destination addresses then you may not be
> able to
> Distribute the traffic.  Especially for long lived flows.
> Try 'port-channel load-balance src-dst-mixed-ip-port' if you are on code
> that supports it.
> Also ensure you have 'port-channel load-balance per-module'.
> You already found the adaptive knob.
> Adaptive is more difficult to troubleshoot when there are issues.
> You may also want to set 'mls ip cef load-sharing full'.
> Mack McBride | Senior Network Architect | ViaWest, Inc.
> O: 720.891.2502 | C: 303.720.2711 | mack.mcbride at viawest.com |
> www.viawest.com
> -----Original Message-----
> From: cisco-nsp [mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of
> james list
> Sent: Friday, July 22, 2016 1:45 AM
> To: cisco-nsp at puck.nether.net
> Subject: [c-nsp] Issue with port-channel hashing
> Dear experts,
> I need help.
> On my C6500 sup720 (12.2(33)SXI5) I’ve a port channel 4 x 1Gbs with 1 Gbs
> full and hashing fixed.
> On the port-channel I’m trunking with few L2 vlans and on top of one of
> those I’ve L3 (with OSPF).
> Since hashing is fixed all the traffic that 6500 Asic has decided to send
> on that link is experiencing problems.
> My questions:
> 1)      Which is the faster and safer way to detect the “guilty” (src/des
> tip) ? I see accounting seems not working
> 2)      What if I would change hashing from fixed to adaptive ? any detail
> on that ? I'm not able to find how it works in detail on cisco.com
> An help is appreciated,
> Cheers
> James
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