DHCP Error - Help Please

[philtomo-25]

We have been getting a strange error recently regarding certain computers not talking (recieving) an IP Address through DHCP,

 

Over the last few days we have installed a new suite of a round 20ish pcs.

 

Our scope is set to dish out addresses from the range

 

*.*.16.1 - *.*.18.1 (thus giving us 700 and odd addresses)

(although no addresses have yet been given from the 17.1 or 18.1 subnet)

 

now we have about 30 addresses still available on the 16.1 range, but when we have request the PCs in the new suite to pick up addresses from DHCP it comes up with the error

 

"unable to contact your DHCP server, request has timed out"

 

Then a default (APIPA) address is issued of IP - 10.0.0.* 255.255.0.0

 

This has happened with other PCs other than the new ones so im sure its not the new pc configuration, but also at the same time other PCs on the network have been given Addresses via DHCP??

 

Tried

Client firewall is off

re-installed the network adapter

swapped switches in network cab

 

Any help would be apreciated

 

phil

[Jon]

Then a default (APIPA) address is issued of IP - 10.0.0.* 255.255.0.0

 

 

phil

 

This sound very strange to me as if you are getting an address in the 10.0.0 range this is not APIPA. An APIPA address would be in the range of 169.254.x.y

 

Maybe you have a stray DHCP server on your network somewhere, some routers and wirless access points come with a DHCP server activated by default.

[Oops_my_bad]

Are you part of your LEA's network? If so and it's flat you might be getting DHCP leases from another school :eek:

[Guest AustenLowe]

is that one big subnet from say 172.16.16.1 - 172.16.18.254 ? or three little C's on the same line?

[sahmeepee]

It might be worth running Wireshark on your DHCP server to see what it's doing. Make a note of the MAC address of a client PC (from the top of "route print") then boot it while wireshark is running and filter the results.

 

That subnet of yours also looks a bit strange. Does it go from 16.1 to 18.255 or 16.1 to 17.255 or is it 3 class Cs? I'm not sure there's a valid subnet mask that will give you 16.1 to 18.255:

 

a /22 network (255.255.252.0 subnet mask) gives you 4 class C's worth (ish)

a /23 network (255.255.254.0 subnet mask) gives you 2 class C's worth (ish)

a /24 network (255.255.255.0 subnet mask) gives you 1 class C worth

[Bestbett]

also worth ipconfig /all and ensuring your getting the ip on the LAN adaptor and not wireless, 10.0 is usually a wireless default dhcp scope.