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Beginner

3850 Switch with DHCP odd behavior

1. If the VLAN was out of scope, addresses would not be handed out, which is happening successfully.

2. If VLAN was shut down, addresses would not be handedout.

Addresses are being handed out.  Just not enough of them.

It is not a layer 2 issue.

Highlighted
VIP Mentor

Re: 3850 Switch with DHCP odd behavior

Hello

"Again, that shortens the lease, but doesn't solve the problem.
When my office is filled with staff, there still won't be enough addresses, as the system isn't handing out the full range"

A good possibility is due to the high dhcp lease of 2 days and if you have mobile clients this would make exhaustion even more so.

I would suggest to shorten the lease time to a low value (maybe 3hours given the size of your scope it looks like you could take the extra BW) and clear the binding database again and force the clients to renew also (ip config /release/renew)

If this resolve your issue then increase the scope back to a more applicable level

Res
Paul




kind regards
Paul

Please rate and mark posts accordingly if you have found any of the information provided useful.
It will hopefully assist others with similar issues in the future
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Beginner

3850 Switch with DHCP odd behavior

Ok, maybe what I'm telling you isn't sinking in.

There are probably 100 clients in the office.  These clients get one address each.  Oftentimes, all 100 will be in the office at once.  When they are all there, it doesn't matter if the lease is 5 minutes or 5 days, as they are all there.  At those times, 100 addresses would be needed.  Once we get above a certain level (say 70), there are no more addresses available.  (These are just figurative numbers, I'd need to go back to figure out the exact ones, something like 106 or 108 is the maximum being handed out).

The lease time will have no affect on this.  As the problem occurs when everyone is in the office, not when everyone transitions in and out. 

The problem is the DHCP server on the switch doesn't believe it has enough addresses to hand out, as the excluded number is way too high. 

Highlighted
Beginner

I know this is a very old

I know this is a very old thread, I ran across it today because I was having the same problem with a 3850 that I run DHCP on.

 

I have a 20 address pool to hand out IPs for our WAPs.  All the WAPs went down after a circuit outage and after doing some research I noticed that my pool said that all IPs were excluded.

 

Pool WAPs :
 Utilization mark (high/low)    : 100 / 0
 Subnet size (first/next)       : 0 / 0
 Total addresses                : 254
 Leased addresses               : 0
 Excluded addresses             : 254
 Pending event                  : none
 1 subnet is currently in the pool :
 Current index     IP address range                    Leased/Excluded/Total
 0.0.0.0           10.48.38.1       - 10.48.38.254      0 / 254 / 254 

 

Turns out that the switch put all the IPs on to the ip dhcp conflict list. (don't know if this was caused by the outage, still researching) According to some documentation I read, once an IP is on the conflict list it gets excluded from the pool and will not be available again until an admin manually clears it with "clear ip dhcp conflict *".  Once I did this my pool returned to the way it was supposed to be and my WAPs came back up.

 

Pool WAPs :
 Utilization mark (high/low)    : 100 / 0
 Subnet size (first/next)       : 0 / 0
 Total addresses                : 254
 Leased addresses               : 18
 Excluded addresses             : 234
 Pending event                  : none
 1 subnet is currently in the pool :
 Current index     IP address range                    Leased/Excluded/Total
 10.48.38.38       10.48.38.1       - 10.48.38.254      18 / 234 / 254 

 

I don't know if this helps, but, I figured I would post just incase anyone else stumbles across this thread like I did.

-David

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Enthusiast

Re: I know this is a very old

I have the same problem
Highlighted
Beginner

Re: I know this is a very old

Thank you David, this helped me solve an issue that I've had for over 6 months !

I also found this, RE: Auto clearing the conflict list... https://community.cisco.com/t5/network-management/auto-clear-ip-dhcp-conflict/m-p/1530142/highlight/true#M73363

Thad
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