I'm trying to find out if it is somehow possible for some switch (Cisco 3750-48) ports to "loose" their "switchport access VLAN 123" setting. I had a switch recently which had 40 ports in VLAN 44 and 8 ports in VLAN 123. I got a call to say the users in the VLAN 123 had lost their connection - when I checked (maybe an hour later) I found these 8 ports also had "access VLAN 44" in the config. If 44 was the native VLAN, could the switch somehow, if there was some error, reconfigure the ports access VLAN 44. My guess is that someone actually reconfigured the ports to access VLAN 44 but there are only one or two people who could do this and neither of them are owning up. TIA, Ned
Port looses VLAN setting
Feb 18, 2009
7 Replies
Do you have some 802.1x in your switch config or any other kind of VLAN autoassignment?
As the other poster pointed out, 802.1x or secondary vlans could be at play, but much more likely to be a changed config or an unsaved config w/ a reboot.
Yes, I have 802.1 trunks on this switch
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I don't think there was a reboot - when I was fixing the problem (switchport access vlan 123) from the console, I'm fairly sure I saw a console message "VLAN1 interface down" ... followed soon by an "VLAN1 interface up". Can you explain further what you mean by "802.1x or secondary vlans...". I would love to be able to recreate the problem and prove nobody was messing with the config... Ned
I've never seen a cisco switch change its VLAN settings in the 10+ years I've been using Cisco switches doing VLANs across thousands of ports that I've configured.
RANCID is great at tracking changes for your switches/routers. It doesn't log every command, there are other solutions for that, but knowing when something changed is good. Make sure you use seperate admin usernames and you pick up the last person who did make a change in comments at the top of the config as well.
By "loose" do you mean broadcast the seeting for others to see?
It sounds like it didn't loose its setting at all, but rather it did lose its setting.
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