We have some Cisco 2960 switches running c2960s-universalk9-mz.122-55.SE7.bin. We downgraded to this from c2960s-universalk9-mz.122-58.SE2.bin at the advice of our support provider when this issue first started. Sometimes, a couple of VLANs on a switch will lost all connectivity to the rest of the network. There are no errors in the log, spanning tree looks completely normal, etc. The only thing that brings connectivity back is either rebooting the switch or deleting the affected VLANs from the switch and adding them back in. Once either of those happens it is like everything is back to normal. This has happened on both stacked and stand-alone 2960 switches. Has anyone ever heard of this? I'd like to hear any suggestions as to where to go next.
I would suggest you to try the following approach. Identifie a particular "broken" VLAN ID, source and destination MAC addresses pair and investigate starting from there. You should be aware what are incoming and outgoing interfaces for this flow supposed to be.
! Check interfaces statistics
show interface status
show interfaces counters
show interfaces counters errors
! Verify STP
show spanning-tree vlan details
show spanning-tree interface
! Verify CAM table population
show mac address-table interface
show mac address-table dynamic address - from previous output
! Verify if the outgoing interface are programmed correctly
show platform forward
If still you won't be able to find out the reason for the issue, please, open a TAC service request.
Thank you both very much. A TAC case is already open and is making zero progress. With that said, I am working on sanitizing the config from our core. I am attaching a cheesy diagram of the setup, which is fairly simple. The VLANs in question only exist on the switches depicted in the diagram, not on any others.
As far as the switches go, there are basically zero errors on any interfaces in the affected vlans:
GigabitEthernet1/0/1 is up, line protocol is up (connected)
Hardware is Gigabit Ethernet, address is c40a.cbXX.XXXX (bia c40a.cbXX.XXXX)
MTU 1500 bytes, BW 100000 Kbit, DLY 100 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation ARPA, loopback not set
Keepalive set (10 sec)
Full-duplex, 100Mb/s, media type is 10/100/1000BaseTX
input flow-control is off, output flow-control is unsupported
ARP type: ARPA, ARP Timeout 04:00:00
Last input 00:00:19, output 00:00:00, output hang never
Last clearing of "show interface" counters never
Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 283
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