Problem accessing network using Linux

Ok, here at work, we have Windows computers which login into a MS domain server.

Some of us also have Linux boxes which get a ip address
from the dhcp server. We can see other boxes and see the internet until about 1 week ago.

Now, we still get a ip address but can't see anything within our own network or on the internet.

My question is how did they do this? How can they accept packets from my windows box but deny packets from my linux box. (This has happened to about 20 of us..)

Thanks.

check your default router on your linux boxes

ifconfig -a

Thats a good start

I had a linux box not pick up on the default router settings from a windows dhcp server.

It says:
[/root]: netstat -rn
Kernel IP routing table
Destination Gateway Genmask Flags MSS Window irtt Iface
165.136.53.x 0.0.0.0 255.255.255.0 U 40 0 0 eth0
127.0.0.0 0.0.0.0 255.0.0.0 U 40 0 0 lo
0.0.0.0 165.136.53.xxx 0.0.0.0 UG 40 0 0 eth0

The 3rd line is my default, correct? (On Sun, it actually says
default but for Linux, it just says 0.0.0.0..)

That 165 address is supposed to be my gateway, I know that.

That looks right..hmm, your sure of the default gateway, yes?

0.0.0.0 165.136.53.xxx 0.0.0.0 UG 40 0 0 eth0

have you tried to renew your dhcp lease? Or has any of your network engineers changed anything? Subnet mask? Seems like a lot of possible variables...

you can also get ethereal or some other packet sniffer to show you where the hell your traffic is going...ethereal can give you quit a bit of info.