For austrian ISP chello net-misc/pump failes to retrieve a network adress on startup. Calling pump directly (pump -i eth0) gets an adress. Further investigation shows that the problem resides in rc-scripts/pump.sh Disabling in rc-scripts/pump.sh the line setting --win-client-ident solves the problem.
you neglected to post `emerge info` or your /etc/conf.d/net
Do other dhcp clients work like dhcpcd, udhcpc or dhclient?
Need more info about this