Re: DHCP client receving address from one server and scope options from another

Bill,

Thanks very much for your response, I should have thought of
DHCPINFORM. In hopes of getting a clearer picture of what was
happening, I used Ethereal to do a packet capture of the related
traffic. First I released the address on the client, started the
packet capture, did an ipconfig /renew, and then waited until the DNS
scope options changed.

Here is what I found:

8:13:55AM
Client sent DHCPDISCOVER
Client sent DHCPREQUEST
Client sent Gratuitous ARP

8:41:48AM
Client sent DHCPINFORM
Server C sends ACK (Server with which the IP is registered)
Client sent ARP reply to Server B (The server which overwrites DNS
scope options)
Server B sends ACK

8:41:51AM
Client sent DHCPINFORM
Server C sends ACK
Server B sends ACK

A couple things that I would like to understand, please chime in if
anyone has any details.

1. Why does a client send a DHCPINFORM request nearly a half hour
after renewing the address?
2. Why after receiving DHCPINFORM ACK notices from two servers, would
the client send out another DHCPINFORM reuqest a few seconds later?
3. When the client receives the secondary DHCPINFORM ACK from Server B
which overwrites the DNS scope options, why does the order of the WINS
options not change on the client as well?

Thanks!
Troy.


Bill Grant wrote:
When a client boots up, it broadcasts on the network to get its config
from a DHCP server. The DHCP server replies with an offer.

In addition, a client can send a DHCPINFORM message (after it gets its
initial config) to receive additional information from a DHCP server. This
info may come from a different source. As an example, a remote client might
get its original config from a remote access server, then obtain additional
LAN-based settings from the DHCP server on the LAN using DHCPINFORM.

usenetposter2006@xxxxxxxx wrote:
I am having trouble understanding something that is occuring on one of
my client computers. I am in the process of bringing a new Windows
2003 R2 DC online to replace an old Windows 2000 DC. Both servers are
running DHCP (with non-overlapping scopes), DNS, WINS. There is
another Windows 2000 server on the same network offering the same
services. My previous setup is as follows:

All DHCP servers have non-overlapping scopes and each scope provides
scope options to point DHCP clients to DNS and WINS servers. When a
DHCP server offers a client an address, the options that it sends
always list the DHCP server as the primary server for DNS and WINS.
So for example, Server A gives out an address and the DNS options for
it would be Server A as the primary, and Server B as the secondary.
This has always worked without any problems. With the addition of
the new server I am seeing some very strange behaviour. In
particular, one client is getting a DHCP address from Server C (the
new server), but it's getting it's DNS scope options from Server B.
The WINS scope options on the other hand are coming from Server C as
they should be.

If I release and renew the IP address on the affected client, it gets
all of the proper settings. It gets all scope options from Server C.
But, a few minutes later (5-15) when I check the client using IPCONFIG
/ALL, the DNS options have changed to those offered by Server B.

Does anyone have any insight into why this is happening, or any
suggestions for how I would troubleshoot? There are no errors in the
event logs on the clients or servers, and dns resolution on all
servers seems to be working fine when checked with NSLOOKUP.

Thanks,
Troy.

.

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