Non-existant computers still pingable

[Guest]

I have 2 DHCP servers in my W2K network, each with their own scope. I have 2
issues currently. One is that I seem to be able to ping a user workstation
by name, that does not exist, and get a response, and the other is that I
have a reservation in for a particular user's computer, but the reservation
is not used.

For the 1st issue, the name I chose to ping, eg starksd is the old name of
an XP workstation. The computer account does not even exist in AD anymore,
but I am able to ping the name, and get a response back with a valid IP
within the scope of one of the DHCP servers. The name does not appear in the
address leases at all. The information in the DHCP server actually tells me
that the IP address is assigned ot another machine. If I ping that machine I
also get a response, with the same IP as the non-existant one. I did NOT
change the name of the computer in question. Starksd was an old computer
that was disposed of.
I am also able to find old names for computers in AD, and when I try and
ping them, I don't get a response (and I shouldn't) but I do see that it
tries to ping a particular IP address.

2nd issue is a little stranger. I have a windows XP computer that was
running service pack 1. I set up a DHCP reservation for it based on MAC
address. Once the reservation was in place, I released and renewed the IP
from the client, and it came back with the same IP, and DHCP showed the
reservation was active. Now, the client machine has a different IP address,
is running service pack 2 with the firewall OFF. If I release and renew, it
will NOT pick up the reservation I set for it.

Can anyone explain why either of these 2 situations are happening? The
second one I could fix by deleting the reservation and making a new one based
on the new IP address of the client, but then I will have to edit the PIX
firewall config as this machine has certain privilleges in terms of network
access that others do not.

Thanks

 

[Doug Sherman [MVP]]

The ping command doesn't care about DHCP. If you have a hosts file entry or
a DNS host record for the old machine and the record points to an existing
IP address, you will get a ping echo.

As to the MAC address issue, this can and probably has been changed for
Windows networking purposes. You can change it back to the original or
whatever you want by editing the registry on the client machine. See:

http://www.nthelp.com/NT6/change_mac_w2k.htm

Doug Sherman
MCSE Win2k/NT4.0, MCSA, MCP+I, MVP

 

[Phillip Windell]

an XP workstation. The computer account does not even exist in AD anymore,
but I am able to ping the name, and get a response back with a valid IP
within the scope of one of the DHCP servers. The name does not appear in the
address leases at all. The information in the DHCP server actually tells me
that the IP address is assigned ot another machine.

AD has nothing to do with it.
You probably have the old name still listed in WINS. You ping the old name,
WINS resolves it the the original IP#,...the "current" machine (shown in
DHCP) is responding to the Ping.

2nd issue is a little stranger. I have a windows XP computer that was
running service pack 1. I set up a DHCP reservation for it based on MAC
address. Once the reservation was in place, I released and renewed the IP
from the client, and it came back with the same IP, and DHCP showed the
reservation was active. Now, the client machine has a different IP address,
is running service pack 2 with the firewall OFF. If I release and renew, it
will NOT pick up the reservation I set for it.

You probably used the wrong MAC address or have the MAC mispelled in the
reservation.

 

[Guest]

Re the MAC address issue, are you saying that the client machine now has a
new MAC address?? When I run ipconfig /all I see the same MAC address as is
assigned in DHCP for the reservation. I even had someone else check it to
make sure I wasn't just seeing what I wanted to see!

As for the DNS issue, I have 2 DNS servers, which are also the DHCP servers.
I am beginning to think that these were not set up correctly. There are old
entries in DNS as you predicted. Is there a white paper or something like
that which refers to how to set up 2 DNS servers, one as primary and one as
backup, so I can check our configuration and make sure it is ok?

It seems as though DNS is not refreshing, or something like that.

 

[Phillip Windell]

As for the DNS issue, I have 2 DNS servers, which are also the DHCP servers.
I am beginning to think that these were not set up correctly. There are old
entries in DNS as you predicted. Is there a white paper or something like
that which refers to how to set up 2 DNS servers, one as primary and one as
backup, so I can check our configuration and make sure it is ok?

DNS has nothing to do with DHCP. You can run DHCP and not have any Domains,
any DNS Server, and no windows machines at all.

If something is screwed up it is DHCP and *only* DHCP. It stands alone
independent of anything else.

 

[Doug Sherman [MVP]]

I guess my theory about the MAC address issue was wrong - don't know the
answer for your situation unless the reservation is not configured correctly
or there are duplicate MAC addresses on the network. See:

http://support.microsoft.com/default.aspx?scid=kb;en-us;164903

As for DNS/DHCP, the manner in which dynamic DNS records are updated in a
DHCP environment is affected by both DHCP server and client settings. See:

http://support.microsoft.com/default.aspx?scid=kb;en-us;228803

If the stale records are primarily machines which have been retired or had
their names changed, you can probably address the issue with scavenging -
See:

http://support.microsoft.com/default.aspx?scid=kb;en-us;228803

Doug Sherman
MCSE Win2k/NT4.0, MCSA, MCP+I, MVP