Subject: dhcp win95 can't move server

From: Dirk Stueven <[email-masked]>
Date: Wed, 18 Nov 1998 11:33:02 -0500 (EST)

Hello,
 
I have a strange behavior of the WIN95 DHCP client. We have two DHCP
servers running in one subnet with non overlapping IP ranges. The clients are
win95 based, the server is AIX. Now I tried to move one of the DHCP servers to
another machine (different server IP address). What happens is that the
client recognises that the server has gone (lease time out). Then it sends a
DHCPREQUEST asking for his old client address. Both servers are not willing to
give that address, one is not allowed (address is not in it's range), the
other one can't because it has allready given that address to another client.
So there is no offer and the client is not sending a DHCPDISCOVER after
this! 
If I move the client to another subnet, everything works fine with a DHCP
server for that network. 
It seems that the client keeps track of all addresses it gets, looks if it
comes back to a known subnet. In this case it will ask for the address it
got last time and will give up if it will not get it --- stupid! 
>From some other sources I believe that this problem might go away with IP
stack V.2, but that is no solution for me, I've got too many clients out
there. 
I am quite shure that it can be solved by editing the registry but I do
not know what to change. 

Has anybody an Idea out there? 

Best Regards
Dirk Stueven
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From: Ye Gu <[email-masked]>
Date: Wed, 18 Nov 1998 18:47:50 -0500 (EST)

Most likely it is due to the DHCP Server not sending a NACK 
to a INIT-REBOOT request that is asking for an address 
already given out to some other client.

If that server would send a NACK, the dhcp client would 
restart from scratch.

Having network sniffs would tell exactly what is
happening.

Thanks!

Ye

-----Original Message-----
From: Dirk Stueven [mailto:[email-masked]]
Sent: Wednesday, November 18, 1998 8:34 AM
To: Multiple recipients of list
Subject: dhcp win95 can't move server

Hello,
 
I have a strange behavior of the WIN95 DHCP client. We have two DHCP
servers running in one subnet with non overlapping IP ranges. The clients
are
win95 based, the server is AIX. Now I tried to move one of the DHCP servers
to
another machine (different server IP address). What happens is that the
client recognises that the server has gone (lease time out). Then it sends a
DHCPREQUEST asking for his old client address. Both servers are not willing
to
give that address, one is not allowed (address is not in it's range), the
other one can't because it has allready given that address to another
client.
So there is no offer and the client is not sending a DHCPDISCOVER after
this! 
If I move the client to another subnet, everything works fine with a DHCP
server for that network. 
It seems that the client keeps track of all addresses it gets, looks if it
comes back to a known subnet. In this case it will ask for the address it
got last time and will give up if it will not get it --- stupid! 

Best Regards
Dirk Stueven
---

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From: Dirk Stueven <[email-masked]>
Date: Thu, 19 Nov 1998 11:10:03 -0500 (EST)

The new DHCP Server is NOT sending a DHCPNACK message. After my
understanding of the RFC2131 this is only a MAY feature. But when the client does not
receive any ACK or NOACK message it should time out and get back to init
state. Below you find the original text from the RFC.
Any Ideas how to get the client back to init state?

"If the client receives neither a DHCPACK or a DHCPNAK message after
employing the retransmission algorithm, the client reverts to INIT state and
restarts the initialization process.  The client SHOULD notify the user that the
initialization process has failed and is restarting."
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---

From: Ye Gu <[email-masked]>
Date: Thu, 19 Nov 1998 12:57:38 -0500 (EST)

The section immediate following what you quoted below describes how client
should reuse a previously allocated address.  It says:
      If the client receives neither a DHCPACK or a DHCPNAK message
      after employing the retransmission algorithm, the client MAY
      choose to use the previously allocated network address and
      configuration parameters for the remainder of the unexpired lease.

This is what we do on the Win95 client.  It goes back to init state when it
can't contact a DHCP server and its lease has expired.

-----Original Message-----
From: Dirk Stueven [mailto:[email-masked]]
Sent: Thursday, November 19, 1998 8:17 AM
To: Multiple recipients of list
Subject: RE: dhcp win95 can't move server

understanding of the RFC2131 this is only a MAY feature. But when the client
does not

restarts the initialization process.  The client SHOULD notify the user that
the