Cisco 4510 ports flooding during backups

[Michael Lydon]

Have a Cisco 4510R+E switch, Sup 7E, running IOS version 3.02.09.SG.   We have a pretty simple network...all servers and PCs are plugged directly into this switch on the default vlan with the exception of one additional Cisco 2960 switch for a group of PCs on the other side of the building which are on VLAN2.  At night during hyperv host backups, our Solarwinds NPM reports millions of transmit discards on just about every active port on the 4500 switch (verified with the sh interface command looking at Total output drops).    If I run a backup of a server during the day...everything grinds to a halt...even accessing servers we aren't backing up.   We previously were on an older iOS version which I upgraded to the 3.02.09...both did the same thing.  Any ideas on why every single port would be flooded during a single server backup?   

[Joseph W. Doherty]

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Posting

Sounds like unicast flooding.

If the backup device just accepts packets, adn doesn't transmit any packets, or transmits very infrequently, the switch will age its MAC out of the MAC table and flood to all ports.

One solution is to sync your ARP and MAC timeout timers.

[Michael Lydon]

Set the MAC timeout to 14400 to match ARP and this didn't resolve the issue.  I'll try setting the mac timeout a little longer and see if it helps.  

[Joseph W. Doherty]

Disclaimer

The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.

Liability Disclaimer

In no event shall Author be liable for any damages whatsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.

Posting

Does the backup send to an IP?

Does this happen immediately when backup starts too?

[Michael Lydon]

The backup is Backup Exec...we have a single backup server...and agents deployed on our other servers.   The issue seems to occur only when 2 particular servers are being backed up...both are our only Hyper-V host servers.  It'll happen maybe about an hour after the backups start on those servers.   When backing up stand alones, there doesn't seem to be any problems.

We just installed Solarwinds monitoring this week so I'll have a more concrete understanding of timeframes in a few days.