I have installed RHEL 4 U2 AS on a new machine. The problem I am having is that when I boot the machine, I won't get an IP from the router.I have to unplug the cable from the nic or the router, plug it back in, and ifconfig it up. Any ideas why it would do this? For reference:

etc/sysconfig/network-scripts/ifcg-eth0

DEVICE=eth0
BOOTPROTO=dhcp
HWADDR=00:30:1B:3E:46:1D
ONBOOT=yes
TYPE=Ethernet

dmesg:

eth0: RealTek RTL8139 at 0xb000, 00:30:1b:3e:46:1d, IRQ 10
eth0: Identified 8139 chip type 'RTL-8100B/8139D'
eth0: link up, 100Mbps, full-duplex, lpa 0x41E1
eth0: no IPv6 routers present
eth0: link up, 100Mbps, full-duplex, lpa 0x41E1
eth0: no IPv6 routers present
eth0: link down
eth0: link up, 100Mbps, full-duplex, lpa 0x41E1

Grep DHCP in /var/log at least. There may be a bunch of reasons, for example incorrect DHCP client version, your host not in the list on dhcp server (I don't know if routers can be this smart). Also you can run 'dhclient eth0' and view output instead of grepping - it'll be some useful information.