DHCP Lease Renew Issues

[APurk]

Hi,

I have a simple network setup whereby I have a router (not netgear) serving the Netgear switch an IP address via DHCP server.

For reasons I won't detail, I require this to have a short lease time, i.e. 120 seconds.

The issues I have been seeing is that the lease time runs out, and the Netgear has to run a "DHCPdiscover" cycle again to be assigned an IP address with a new lease, therefore leaving me with communication dropout which I cannot tolerate in the application I am using this setup in.

Should the Netgear switch not be renewing the lease with 50% of the lease expired (T1?) and again with 85% of the lease expired (T2?) which I have read regarding windows machines.

I can't seem to find any information relating to this topic in the Netgear manuals, be it CLI or Web config manuals.

Should I be looking at the ARP timeout? Is it this that should be reduced also, as I read it is default 1200 seconds. If this is reduced to <120 seconds would this cause a DHCP lease renew?

Many thanks

APurk

[Retired_Member]

Hi APurk,

Welcome to the community!

Do you mean when DHCP Server set lease time to 120s, the Switch cannot get IP address agian when time over 120s?

I think if Switch can refresh the IP address agian, and the function is ok, right?

So could you please check agian whether Switch can refresh IP address or not when timer over 120s?

Hope it helps!

Regards,

EricZ

NETGEAR employee

[APurk]

Hi Eric,

Sorry if I wasn't clear enough.

The following is paraphrasing from the logs of the DHCP server:

Netgear -> DHCP Discover

Server -> DHCP Offer

Netgear -> DHCP Req

Server -> DHCP Ack (with 120s set lease time)

approx 125 seconds pass with no further DHCP traffic until the Netgear goes through the cycle of DHCP Discover to acknowledge again. However this is done only after the lease has expired and communications have dropped for multiple seconds. The link does re-establish, however the comms loss as I said is not acceptable in the application I am using it in.

I was expecting the switch to do something along the lines of the following:

Netgear -> DHCP Discover

Server -> DHCP Offer

Netgear -> DHCP Req

Server -> DHCP Ack (with 120s set lease time)

60 seconds pass

Netgear -> DHCP Req

Server (if still present) -> DHCP Ack (renewing the 120s lease time)

60 seconds pass

etc.

etc.

My problem seems to be that the Netgear switch is not sending a message back to the server for a new lease request while there is still time remaining on the original lease. Are there any default set, or minimum set times within the Netgear which would be causing me this issue?

I can't remember exactly which firmware version I am running, but it is major version 10.

Many thanks

APurk

[Retired_Member]

Hi APurk,

Thanks for your quickly response!

Now I am clearly with your detailed description.

Did you capture DHCP packet on Server?  And found that Switch didn't send DHCP Req to Server when 60 seconds pass?

Could you please provide your capture packet to us?

I also test in my side, it's ok. I use same Switch but with v11.0 firmware, and Switch can send DHCP Req to Server with 60 seconds pass.

Below is the ScreenShot for capture packet on Server.

[APurk]

I shall check up on the setup, and try wireshark out on it.

I only had the logs the DHCP server produced which I detailed above.

Hopefully be able to update later today.