6509 DHCP

DAvelarNIC · ‎06-25-2014

Hello again.

I had a question for the community that maybe someone can assist with. We have a 6509 that acts as a DHCP server for all devices. Recently it appears that printers that are set to DHCP have been losing their assigned IP's way before the lease expiration. Lease expiration is set to 60 days. The printers are not restarting or being powered off. The switches they are connected to are not indicating a drop connection. Has anyone experienced anything like this before?

Thanks

Lovleen Arora · ‎06-25-2014

Since the IP address is only leased from the server, the lease must be renewed from time to time. When one half of the lease time has expired (T1=0.5 x LT), the client will try to renew the lease. The client enters the Renewing state and sends a DHCPREQUEST message to the server, which holds the current lease. The sever will reply to the request to renew with a DHCPACK message if it agrees to renew the lease. The DHCPACK message will contain the new lease and any new configuration parameters, in the event that any changes are made to the server during the time of the previous lease. If the client is unable to reach the server holding the lease for some reason, it will attempt to renew the address from any DHCP server after the original DHCP server has not responded to the renewal requests within a time T2. The default value of T2 is ( 7/8 x LT). This means T1 < T2< LT

DAvelarNIC · ‎06-26-2014

Thank you for the response lovleen. I read this as well but what I would like to know is why is it losing its assigned IP even before the 30 day mark of the 60 lease time. If the DHCP server (6509) is assigning a DHCP address to a node for 60 days I don't see why it would not respond to a node even after it has been reset. Shouldn't the 6509 know that MAC address XXXX has been assigned IP XXXX and just reassign it?

I am not sure why the client does not want to have static IP assignments for printers. I know this would help avoid this issue but to create exceptions on Cisco for several hundred printers would not be feasible at this time.

Renan Abreu · ‎06-26-2014

Did you check if the bindings are being lost? Are you saving the bindings to the database? Maybe you're not and reloading the device will make you lose it. Is the ping test enable on the 65xx? It should be by default "ip dhcp ping timeout xxx"

DAvelarNIC · ‎06-26-2014

I think that might be it. On this particular switch it was not set to save the bindings to the db. I just corrected it and will monitor.

I don't see the IP DHCP PING TIMEOUT option. Is it necessary and what should the timeout be set to?

Renan Abreu · ‎06-26-2014

It is configured by default, so if you don't see it, probably it is configured

Renan Abreu · ‎06-25-2014

Hi DAvelarNIC,

I see you have already an answer, but talking about printers, wouldn't it be better to statically assign the IP addresses and create an exclusion on the 6500?