[c-nsp] Unicast traffic being sent to every port? Aging issue?

[Chris Woodfield]

Replying to an old thread...

I'm seeing a very similar situation caused not by ZFS but by a dual-switch model resulting in one switch never seeing the frames that come in over the other since their least-cost routing hop is on the same switch. We've tuned our CAM and ARP timeouts to prevent this normally, but spanning-tree events/TCNs put all of those CAM entries into a fast-aging queue, which results in traffic to each host flooding until the ARP entry times out. Clearing the ARP table manually is a fix, but not exactly without its own impact.

However, while researching the issue I found this paragraph in Cisco's docs:

"Note: In MSFC IOS, there is an optimization that will trigger VLAN interfaces to repopulate their ARP tables when there is a TCN in the respective VLAN. This limits flooding in case of TCNs, as there will be an ARP broadcast and the host MAC address will be relearned as the hosts reply to ARP."

http://www.cisco.com/en/US/products/hw/switches/ps700/products_tech_note09186a00801d0808.shtml#cause2

Given that the switches in question are Cat6Ks running SX code, any reason the above might either not be working or not helping us even if it is? Is there a command needed to enable this optimization?

Thanks,

-C

On Mar 23, 2010, at 4:12 PM, Gert Doering wrote:

> Hi,
> 
> On Mon, Mar 22, 2010 at 07:03:36PM -0700, Ray Van Dolson wrote:
>> What's happening is, esx1/2 beging talking to zfs1.  All is well for a
>> while... but at some point, zfs1's MAC address expires from the CAM on
>> the switch (I guess that is what is happening).
> 
> If zfs is only receiving packets, yes, that's likely to happen.
> 
> What we do is easy: install something like rwhod that broadcasts a 
> single packet every minute.  Make sure all CAM tables are always up
> to date.
> 
> gert
> -- 
> USENET is *not* the non-clickable part of WWW!
>                                                           //www.muc.de/~gert/
> Gert Doering - Munich, Germany                             gert at greenie.muc.de
> fax: +49-89-35655025                        gert at net.informatik.tu-muenchen.de
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