PPP problem

[Alexei Nefediev <nefediev heron itep ru>]

Hello,

does anybody know what can be wrong with PPP under RH 5.1? 
I have 

initscripts-3.67-1
ppp-2.3.5-1
net-tools-1.432-2

installed. When I try to get connected I see that pokets are being sent
and received, but IP address is not assign to my computer. Quite the same
configuration (I mean all config files with IP addresses, DNS's etc, and
even with the same kernel loaded) leads to NO problems under RH 5.0.

What could it mean?
What else packets affect PPP connection?

Thanks in advance,
Alexei