Hello everyone. We have faced some strange problem. ill try to explain situation in details . We have network where ip configuration occurs using dhcp protocol. As dhcp clients we have some routers(Dlink,Microtic,Netgear,Trendet), XP Machines(SP2/SP3), Win 7 and Vista machines. An on vista an Win7 some strange dhcp ip lease time borders accidantly can be observed. We set lease tim on server to 15 min(its easy to get the problem with such lease times casue of short renew interval instead of 7 days:)) and client succesefully obtain ip at dhcp start, so we see ok handshake in dump: Discover from client Offer answer from server Request from client Ack from server. At this pint everything is ok. From that point as we know clients side after some period depending on lease time duration(see RFC:)) sends Renew/Update/Verify requests to server, and server ACKs previously send data.Ok: Request from client Ack from server Request from client Ack from server Request from client Ack from server etc... during such renews we can see in ipconfig/all output correct ip lease time start and expire time, so expire-start=15 mins. But accidently something goes wrong and (only observed on vista/win7 machines) ip lease time borders go mad, e.g.: We see,say, current time is 15:20 And here goes Request and Ack answer and.. and we have something crazy like that in ipconfig /all output: Lease obtained <date> 15:50:36 Lease expired <date> 16:45:36 The diff expired-obtaine !=15 min and obtain time is in future O.o Also we met something like that: Lease obtained <date> 15:20:36 Lease expired <date> 16:45:36 The point is that obtained time is correct but expired looks strange. Obtained in such way duration may differ but in such situation settngs a far away from real correct settings. ipconfig /renew fixes the problem, but after some hours the problem may reappear. Iv googled on some forums, a saw something strange with ip lease time behaviour but that was connected with dual boot. In our situation we have only one OS on machine. The strange thing is that such problem doesnt appear(or we havent met) on XP on router boxes. Does anyone know what is that and how to solve the problem? Thanks in advance.

Hi, What is your DHCP server? I suspect this is related to the lease renew process: IP addressing information is leased to a client, and the client is responsible for renewing the lease. By default, DHCP clients try to renew their lease when 50 percent of the lease time has expired. To renew its lease, a DHCP client sends a DHCPRequest message to the DHCP server from which it originally obtained the lease. The DHCP server automatically renews the lease by responding with a DHCPAck message. This DHCPAck message contains the new lease as well as any DHCP option parameters. DHCP Client States in the Lease Process Hope it helps. Alex Zhao Please remember to click Mark as Answer on the post that helps you, and to click Unmark as Answer if a marked post does not actually answer your question. This can be beneficial to other community members reading the thread.

Hi, thanks for the answe, but... Yeah i know how dhcp protocol works that was not the question:) Lease time field in bootp header contains only duration of lease in seconds and there is no info about when it starts and when it ends, its up to dhcp client to set them according to local time. So i think there is mb some bug or conflict between services (like e.g. dhcp-bonjour bootup trouble) which acts like was described. The questions was smthing like: under what conditions dhcp clients side can set such strange ip lease obtained and expired time borders. Wev aslo noticed that such situation occures when there is local time desynchronization between pc and ntp server time. At last when time synched the problem was not observed. Ill post(when get to work) the wireshark/tcpdump dump of renew/ack packets but dont think it will help:( Mb there are some debuggin tools for dhcp (syslog has nothing) or some external monitors or something else which can catch such situation or at least give some detail log about dhcp behaviour? PS its isc server running on debian

Yeah i know how dhcp protocol works that was not the question:) Lease time field in bootp header contains only duration of lease in secodns and there is no info about when it starts and when it ends, its up to dhcp client to set them according to local time. So i think there is mb some bug or conflict between services (like e.g. dhcp-bonjour bootup trouble) which acts like was described. The questions was smthing like: under what conditions dhcp clients side can set such strange ip lease obtained and expired time borders. Wev aslo noticed that such situation occures when local time desynchronization between ntp servers time. At last when time synched the problem was not observed. Ill post the wireshark dump of renew/ack packets but dont think it will help:( Wev stucked cos it Mb there are some debuggin tools for dhcp (syslog has nothing) or some external monitors or something else which can catch such situation or at least give some detail log about dhcp behaviour? PS its isc server running on debian

Seems wev found out the reason. the reson is time changing. 2 situations hand time change or automatic synchronization: First situatoin if during dhcp renew chaing user changes current time forard/backward for some time slice 90% (or mb event 100%) there will bee dhcp session reset - discoever request and of ip settings reset and all connections reset Second situation occurs when there is some desynchronizatin in current time and windows service "corrects" it. That way there may be a discover and connection reset, may be OK or there may be strange situation when obtained and expired lease time siddapears so we cant see them in ipconfig/all output:) That way seems dhcp client lost all info about when there must be update etc ...but some time after there is new handshake(discover-offer-request-ack). What can you tell about such behaviour, especially about situation with automatci time sychronization.Does it work as developers expect? That measn for us that on such PC with time problems DHCP is unstable ...

Hi, We suggest a PSS case be opened to understand the behavior as it goes little too deep for a forum query. Thanks.Ketan Thakkar | Microsoft Online Community Support