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New Member

3750 stack dropping routed packets

The stack consists of a 24TS and a 12S. It has about 40 vlans on it and 25 SVI's. Except for minor changes to access-lists, its config has stayed relatively the same for several years.

I added a 3750E to the stack over the summer and upgraded the firmware. A few weeks ago, when our residential students returned and traffic levels went up drastically, I started getting reports of poor performance, including packet loss of over 30% at times.

In all instances, it seems to be source IP dependent. Two clients on the same distribution switch, one with high loss, and one with no issues. Level 2 connectivity is solid.

I upgraded the firmware again and one of out mailservers now had issues. I removed the 3750E and this was fixed, but the overall issue is continuing.

I downgraded the firmware this morning with no change in operation. I do notice that clearing the ARP table seems to help, but it is only temporary. I've now had 12.2(35,37, and 40) all have the same issue. I have even replaced the stacking cables.

I'm at a loss now. I'm about to build another stack with spares and do a major swap, since I have run out of ideas.

(and the students are about to riot.)



Re: 3750 stack dropping routed packets

From your description, my impression is that this problem is config-related. Access lists are always suspect in this kind of situation.

I noticed that it had been running for quite some time but that says little.

Do away with the access-lists and try again or post the configuration so that we can have a look at it.



New Member

Re: 3750 stack dropping routed packets

I'm still puzzled by the fact that a 'clear arp' will provide temporary relief. How long it lasts seems to be directly related to the overall activity on the particular vlan.

Doing away with the acls could not be done for very long, since this is our primary firewall to the world. Were you saying delete them entirely or just take the access-groups off the svi's?

I will need to spend quite a bit of time sanitizing the config before I could post it here, but its possible.


Super Bronze

Re: 3750 stack dropping routed packets

Are you doing just L2 or L2/L3 on the stack?

What feature image have you been using?

What SDM template are you using?

Any information on the processor load when there's drops?

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