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I have a Cisco C9300 is one of my main racks. Recently it has been restarting on it's own. My suspicion that the PSU is on the way out. Strange part is when it does this the VLAN table resets to default. To fix this I have to local logon to it and then enter the VLAN for the management network, pull down the vlan.dat file and overwrite it on flash. Once that is done I reload the switch. When it restarts it comes up working the way it should. Why when the power cuts out does the VLAN table drop? I have seeing this happen on switches when they have PSU issues on multiple other C9300s we have.

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    I’ve got a few 9300s and have NEVER seen that behavior after a power loss. Furthermore, I’ve never personally seen that behavior on any other model I’ve ever used. Have you looked to see if there’s any known bugs about the VLAN database being lost like that, or opened up a Cisco TAC case yet? Maybe consider upgrading/downgrading the software too, to see if the problem follows. Should be easy to recreate/test by pulling power manually, I’d think.
    – Jesse P.
    Commented Dec 22, 2021 at 22:07
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    I will put in a TAC for it. It is running on the 17.03.03 firmware. I had this issue on the 16.9.3 firmware as well.
    – JukEboX
    Commented Dec 23, 2021 at 16:39
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    That’s interesting. I’ll be looking forward to hearing an update about this and I’ll try to do some research myself.
    – Jesse P.
    Commented Dec 23, 2021 at 18:31
  • Are you running VTP for vlan distribution? Sounds like maybe the switch could be coming up blank if it hasn't learned anything from a VTP server. If you manually put the vlan.dat on there, then it would boot up with them, then, VTP would just wipe the file. Only guessing, just trying to offer ideas. Obviously the crashing would be a separate issue, but they certain could go together if there's a hardware fault with the RAM or something. It doesn't feel to me like a PS issue, but still could be.
    – user3629081
    Commented Nov 19, 2022 at 3:30

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Reset to default
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So the issue was each switch as acting like its own VTP server. The switch would reach out to a non existent VTP server and drop its vlan.dat. The fix we have for this was to change the VTP to tranparent.

vtp mode transparent

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    Cisco best practices now include using transparent mode and restricting VLANs on a trunk to only those used on the switch with the switchport trunk allowed vlan interface command.
    – Ron Maupin ♦
    Commented Nov 22, 2022 at 15:49
  • @RonMaupin we do do that as well.
    – JukEboX
    Commented Nov 22, 2022 at 17:15

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