DHCP Client Differences

Paul Romano ittech68 at yahoo.com
Fri Aug 16 02:49:35 UTC 2013

I am not sure this is the right place to ask, but, is there a single resource that documents the differences or known flaws with different clients?
I have recently seen an issue with Cisco VOIP phones that have a bug and am looking for a master resource for similar issues.
1. Phone boot up and get its IP address from its DHCP server.
2. Then phone set three timers(lease timer, T1,T2) for the IP address lease.
3. When the T1 expired phone goes into RENEWING state and begin to send the DHCP request to extend its lease time.
4. The DHCP server does not give any response for that request.
5. After phone retry 3 times and then it goes into REBINDING state and clear PROGRAMMED flag of its DHCP status.
6. Phone send the DHCP broadcast packets at REBINDING state to the DHCP server and this time the DHCP reply one NAK response to phone.
7. Phone ignore the NAK response and does not go to INIT state since the PROGRAMMED flag is cleared at step 5.
8. After (dhcpLeaseT2 - leaseT1temp)/2 seconds the T1 thread run again and phone go to RENEWING state and repeat above steps(step 2 ~ step 7) again.
9. Phone goes into INIT state after the lease time expired at last.
Phones are running 9.2.1 which does not have fix for this bug.
Recommendation from Cisco TAC is to perform the firmware upgrade to 9.2.3.
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