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sat86 10-01-2005 05:42 AM

DHCP problems - multiple DHCP servers
 
I use my computer on a university network, and it would appear that someone has managed to run their own dhcp server (probably some wireless router or something) on the network. This interferes with my obtaining an IP address from the legitimate server.

However windows appears to get an IP address from the correct place. Why is this the case? ethereal seems to be showing windows DHCP packets only getting sent to the correct address, (does windows cache the DHCP server address?) whereas linux appears to just broadcast for the nearest server.

How can I force linux to use the correct server? (Should the dhclient -s option work? It reports the network is unreachable.)

(My distro is Fedora Core 4 though I'd expect I might just have to use dhclient options rather than use a config tool.)

Thanks

homey 10-01-2005 09:39 AM

I've never actually had to do this but have a look at man dhclient.conf .
In particular, you may need to use reject < ip address > and
server-name

sat86 10-01-2005 01:29 PM

Thanks.

That appears to reject the offers from the rogue server, though the proper one appears not to be responding just now...

I may have to convince it by putting in some client details.

homey 10-01-2005 02:34 PM

Doesn't server-name work?

server-name "string";

The server-name statement specifies the name of the boot server name to use.
This is also not used by the standard client configuration script.

sat86 10-02-2005 05:43 AM

This does not appear to be necessary. It seems that telling the server my MAC address and other such details encourages it to respond. Though for some reason it is possible NOT to instruct dhclient to reject the rogue server and it still takes the legitimate address despite getting two offers. I don't know how it can tell which to choose. Though forcing it to reject the rogue one is a useful safety measure.

Thanks for the help.


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