"Peter" <(E-Mail Removed)> wrote in message
news:A2639206-747D-4383-995A-(E-Mail Removed)...
> Network is in a school, the schools are connected by Cisco 1600 routers,
none are capable of broadcasting DHCP.
> I have chacked all the switches, none are DHCP capable. There is one
wireless access point, it has been removed for troubleshooting, still get
randon 192.168.x.x addresses.
> Pete
3 possibilities come to mind:
1) Rogue DHCP server on LAN ( most likely );
2) Misconfiguration of an authorised DHCP server;
3) DHCP was temp. unavailable, and 192.168.x.x addresses
have been configured in the Alternate Address tab.
When you get a random 192.168.x.x address, do an IPCONFIG/ ALL
and look see what the address of the DHCP server that issued the address.
Is it one of the authorised DHCP servers or is it another address, like
192.168.0.1?
From the machine with the bad 192.168.x.x address,
try pinging the rogue DHCP server. Does it reply?
Common causes of rogue DHCP are:
- Hardware devices like Wireless Access Points ( including the ones you
don't know about :-) )
- Machines with Internet Connection Sharing enabled;
( perhaps a laptop that's only sometimes on the LAN? )
- Users 'experimenting' with downloaded DHCP servers 'for fun'
If you have the IP address of a rogue DHCP server, you can do a
few of things to try to determine what/where it is.
- try pinging it, and then look do an 'arp -a' to see it's MAC address.
The first few digits of the MAC address will tell you the manufacturer
of the device or LAN card.
- try doing an 'nbtstat - A' on the IP address and see if you can get the
machine name.
- try pointing a web browser to the ip address. If it's a hardware type
device, you may get a config or login page that offers up some clue.
- try pinging it continually with ping -t, and then ( after hours
preferably! ) pull the uplink cables
between various switches to determine which switch and port the device is
on.
--
Best Regards,
Ron Lowe
MS-MVP Windows Networking
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