flowcontrol problem on a Cisco 6513

Unanswered Question

I am running an iSCSI SAN and I had to turn on flowcontrol on the switch ports. I've been having some performance problems with one of the servers connected to the iSCSI SAN and I'm trying eliminate a switch problem.

Here's what I get when I do a show flowcontrol:

Port Send FlowControl Receive FlowControl RxPause TxPause

admin oper admin oper

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

Gi9/37 desired on desired desired 0 0

Gi9/38 desired desired desired desired 0 0

Gi9/39 desired on desired desired 0 0

Gi9/40 desired desired desired desired 0 0

Gi9/41 desired on desired off 0 0

Gi9/42 desired desired desired desired 0 0

Gi9/43 desired desired desired desired 0 0

Gi9/44 desired desired desired desired 0 0

Gi9/45 desired desired desired desired 0 0

Gi9/46 desired desired desired desired 0 0

Gi9/47 desired desired desired desired 0 0

Gi9/48 desired desired desired desired 0 0

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

I've been talking to Equallogic tech support and they're telling me the output doesn't make sense. here's what they say:

For all of your iSCSI ports, where you have explicitly set flowcontrol to "receive desired", we should see something in the "oper" column in the Receive Flowcontrol set. They should all report either "desired on" or "desired off". "desired desired" means that no negotiation took place at all.

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On the server side I have Dell servers with Broadcomm Netxtreme Gigabit NICs and their flow control is set to Auto.

I have this problem too.
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Calin Chiorean Tue, 08/26/2008 - 03:34

Hi!

With flowcontrol you have this options:

flowcontrol receive

- desire - allow but not required (so if the other end send flow-control packets, this are accepted but not explicit required during negotiation)

- off / on - disable / enable flow-control packets

and the same for flowcontrol send.

I usually configure the port with flowcontrol receive desire and usual they negotiate ok and I have under the Control Oper field "on"

If you want to force everything configure flowcontrol with on option and see if everything is ok.

Hope that help you a little bit.

Good luck!

Cheers,

Calin

rduke Fri, 09/05/2008 - 07:12

Not running iSCSI; however, this is what some of my ports look like with flow control working on a 48 port card in a 6513.

In any case, the numbers would not be all zero if any flow control were occuring.

I am having problems trying to get flow working on Novell servers. Supposely all you have to do is add a line to the autoexec.ncf file to enable flow on the servers, but the switch will not enable flow-even with a forced setting. This is also using broadcom cards in IBM servers. The funny thing is that flow works on the same hardware with any Windows OS installed. I figured it was a driver issue, but can not find a fix. I am getting a lot of input queue drops which is easy to see with a show interface summary command.

Hope this helps. There does not seem to be a lot of documention about flow control.

Randy

Port Send FlowControl Receive FlowControl RxPause TxPause

admin oper admin oper

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

Gi4/8 desired off off off 0 143216

Gi4/9 desired off off off 0 0

Gi4/10 desired off off off 0 0

Gi4/11 desired on off off 0 1749140

Gi4/12 desired on off off 0 639628

Gi4/13 desired off off off 0 0

Gi4/14 desired on off off 0 3241984

Gi4/15 desired on off off 0 7468796

Gi4/16 desired on off off 0 6481304

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