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OBi110 not requesting new IP address on DHCPNAK

Started by AndyJ, May 02, 2011, 09:33:41 AM

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AndyJ

I have a static lease defined for my OBi110 - that is, the DHCP server always returns the same IP address for the OBi110. At one point, I changed the static lease on the server to use a different IP address, but did not reboot the OBi110. At the halfway point of lease expiration, the OBi110 attempted to renew its lease on the old IP address, and the DHCP server responded with a NAK, since the IP address had changed. That is expected behavior. However, the OBi110 did NOT request the new address after receiving the NAK. It repeated the DHCPREQUEST for the old address 5 times, to which the server NAKed each time, and then gave up and continued using the old IP address.

There are, of course, ramifications of changing the IP address - if calls are active, they will most likely be dropped, and so on. However, the OBi110 should be requesting a new address after receiving a NAK from the DHCP server.

The lease (from the OBi110's perspective) hasn't expired yet, since the lease expiration is 1 day, and it's only been 13 hours since the lease was originally obtained. So, I'm waiting to see what happens at that point... if the OBi110 continues using the address even beyond expiration, or if it finally requests a new address at that point.

AndyJ

This isn't good. I'll have to email support and see if this can get on the list of things to be fixed.

After the failure to renew the IP address, the OBi110 started retrying at decreasing intervals, still ignoring the DHCPNAK. So, after the failure, it tried again 4 h, 30 s later, then 2 h, 15 s later, then 1 h, 7.5 s later, and so on, until it was down to 1 minute. Then, it just gave up, continuing to use the old IP address, never trying to properly obtain a new address.

AndyJ

One more update... after it appeared the OBi110 had given up, it had actually just backed off a bit. An hour and a half after "giving up", it again started trying to renew the address, then again 45 minutes later, then 22.5 minutes later, and so on. However, this time, after reaching one minute it FINALLY sent a DHCPDISCOVER request to get the new address. The server responded with a DHCPOFFER with the new address. At this point, it looks like the OBi110 rebooted itself. When it came back up, it sent another DHCPDISCOVER, received the DHCPOFFER with the new address, and happily started using it.

So, it looks like the OBi110 isn't honoring the DHCPNAK responses, and won't try to get the new address until the original lease actually expires (I'm assuming that's what happened here).

RonR

AndyJ,

I can reproduce the problem with the OBi DHCP client ignoring NAK's until the lease fully expires, at which point the OBi stops responding to the old IP address.  Three minutes later, the OBi reboots and properly obtains a new (and changed) IP address.

I ran the same test on a PAP2 and observed the same behavior except the PAP2 reboots immediately when the lease fully expires.  The is not a coincidence since the OBi developers are the same Sipura/Linksys/Cisco people that developed the PAP2.

I ran the same test on Windows 7 which properly handles NAK's and Windows immediately obtained a new (and changed) IP address.

This does need to be fixed.

Good find!

RonR

obi-support2,

Please acknowledge that you are aware of this problem and looking into it.

Thank you,

Ron

AndyJ

Thanks for confirming the issue, Ron. I emailed support directly and they said they're adding it to their list of things to do.