Giants on Gig links on 720 sups

[kris55s]

We just installed 720 supervisors in our core 6500 switches. On the gig links that interconnect buildings we had alot of input errors and giants. I increased the MTU on the gig links from 1500 to 9216. There are no longer input errors but still giants. The amount of giants is not as large as before.

Anyone have any ideas on what else to do to correct this.

[amit-singh]

Hi,

Do you see the giants on both side of the uplinks or one side only. What is the IOS you are running. Please paste the switch configurations. Did you try clearing the counters after the MTU has been increased.

-amit singh

[kris55s]

The giants are on both ends. I did clear the counters after changing the MTU size. I can not paste the config because this is a DoD network. Is there something specific that you are looking for?

Version 12.2(17a)SX3 is running on all the sup's.

[kris55s]

bump

[amit-singh · Accepted solution]

Hi Kristen,

I have come across a bug for the same issue:

Bug ID: CSCec62587- giants on dot1q trunk with sup720 uplink ports

Symptoms :

A Catalyst 6000 series switch running 12.2(14)SX or 12.2(17)SX codes may report giants for packet received tagged on a trunk over the sup720 ports.

The issue is cosmetic.

The fix will be available in 12.2(18)SXD.

I would suggest it to upgrade to 12.2(18)SXD, and that should solve it.

HTH,Please rate if it does.

-amit singh

[kris55s]

I will try the upgrade. You said the bug is for dot1q. We are running ISL on those trunk links. Could that be the problem? I have wanted to change the encap to dot1q but have not had the time and we are going to be going to routed links in the next several months so the change would be irrelevant when we go to the routed links.

[sundar.palaniappan · Accepted solution]

Kristen,

I had run into the same situation for one our customers a while ago. The switch was logging giants on ISL trunks and I found a bug(cosmetic), not sure if it's the same one posted by Amit above, that explained the reason why the port was logging giants.

I believe these ports, by default, support a MTU of 92xx something. Anytime, the frame size exceeds 1500 bytes the switch logs them as giant and continues to forward the frames. It doesn't affect the traffic and it's just a count of # of frames that exceeded the MTU of 1500 bytes. Of course, our customer decided not to upgrade as the bug was only cosmetic.

HTH

Sundar

[kris55s]

Thanks guys!!! I really appreciate both of your explanations.