Thursday, August 15, 2013

Wireless/Switch Troubleshooting: Vlan Status - "Vlan is up, line protocol is down"

I had this wireless problem (as reported to me) that no one could get on wireless.  When I got onsite, I found that you could get on the wireless networks, but you could not get DHCP from the DHCP server.  So, after troubleshooting the DHCP server (which was fine), the Brocade controller (which was fine), the switches connecting the APs to the network (which was fine) and the APs themselves (which were fine), I got back to the core switch (a Cisco 3550) to try to figure out what the problem was.  I happened to notice in the 'show log' that the vlan did not come up.  So, I did the following:

switch#sh int vlan 40
Vlan40 is up, line protocol is down

Ok, vlan up, line protocol down.  So I thought I would go and put the "switchport access vlan 40" on a port that I knew had a connection to it.  That is when I noticed the message "% Access VLAN does not exist. Creating vlan 40".  Hmmmm.  Now, this was working for a while now without any problems.  What is up with that message?

switch(config-if)#int gig 0/7
switch(config-if)#switch mode acc
switch(config-if)#switch acc vlan 40
% Access VLAN does not exist. Creating vlan 40

switch(config-if)#no switch acc vlan 40
switch(config-if)#switch mode trunk
switch(config-if)#do sh int vlan 40
Vlan40 is up, line protocol is down

Ok, still up, down.  So I go into the vlan database and verify it is in there.  Vlan 40 is in there, but the other vlan (80) is not.  So I create it.  Then I go back into config mode and re-IP the vlan.

switch#vlan data
switch(vlan)#vlan 40
VLAN 40 modified:
switch(vlan)#vlan 80
VLAN 80 added:
    Name: VLAN0080
switch#config t
switch(config)#int vlan 40
switch(config-if)#ip address
switch(config-if)#ip helper-address
switch(config-if)#no shut
switch(config-if)#interface Vlan80
switch(config-if)# ip address
switch(config-if)# ip helper-address
switch(config-if)#no shut
switch#sh int vlan 40
Vlan40 is up, line protocol is up

And this fixed this problem.  Im not sure why it lost only these two Vlans.  I have seen switches loose all Vlans before, but not just a few.  Very odd.

UPDATE*** So another engineer I work with noticed that VTP was set to 'server' on most of the switches.  Apparently, Im assuming that when an update was done on another switch with an added vlan (for voice they are putting in), that did not have the wireless vlans on it, it updated to the core and caused this problem (I am assuming).

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