DCHP overrides default gateway and nameserver on double-nic server.

From: Morten ab Lange (morten_nospam_at_yahoo.com)
Date: 10/16/03 

Date: 15 Oct 2003 19:25:28 -0700

Hello,

I am setting up several Linux boxes ( RedHat Enterprise Linux 2.1,
kernel 2.4.9-e.27) that use two different ethernet interfaces.

eth0 is used for setup and administration purposes and the adress is
obtained by DHCP from a windows 2003 server ( HP/Compaq blade
infrastructrure more or less dictates this ). This all works well,
except for the fact that I also
get a default gateway from the DHCP-server. ( In spite of a config in
the Windows DHCP that seems to say no info on gateway nor nameserver
should be supplied to clients )
This default gatway is for the net that eth0 is on (the "DHCP-net")
but I need to use a gateway on the net where eth1 is as my default gw.

1. Are there any undocumented switches to stop dhcpcd from acting on
info it receives about default gateways ? the PEERDNS=no is supposed
to prevent the same for nameserver info but my /et/resolv.conf is
overwritten all the same.

2. Any workarounds at all ? ( My colleague on the windows side is
working on "tuning" the DHCP server .. ) The only obviuous that I see
(reluctantly) one is to quit using DHCP ...

I guess it is not very commmon to use DHCP on multiple interface
_servers_, so not many "eyeballs" have witnessefd this behaviour yet.
I suspect the problems might be due bugs/deficiencies both in Linux
and Windows (?)

Best Regards ,
Morten

The fragments below should shed some light on the problem :

[root]# cat /etc/sysconfig/network-scripts/ifcfg-eth0
ONBOOT="yes"
DEVICE="eth0"
BOOTPROTO="dhcp"
PEERDNS=no # This does not work as advertised

[root]# cat /etc/sysconfig/network-scripts/ifcfg-eth1
DEVICE=eth1
BOOTPROTO=none
ONBOOT=yes
USERCTL=no
PEERDNS=no
TYPE=Ethernet
IPADDR=172.16.3.136
NETMASK=255.255.255.0
NETWORK=172.16.3.0
BROADCAST=172.16.3.255
# GATEWAY=172.16.3.1 # This has no effect..

[root]# cat /etc/sysconfig/network
NETWORKING="yes"
HOSTNAME="orappt"
GATEWAY=172.16.3.1 # This has no effect
GATEWAYDEV=eth1 # This has no effect

## Correct routing table and /etc/resolv.conf:
Destination Gateway Genmask Flags MSS Window
irtt Iface
172.16.3.0 0.0.0.0 255.255.255.0 U 40 0
0 eth1
172.16.65.0 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
0.0.0.0 172.16.3.1 0.0.0.0 UG 40 0
0 eth1
nameserver 172.16.3.90
nameserver 172.16.3.19
domain example.com

## Incorrect routing table and /etc/resolv.conf:
Destination Gateway Genmask Flags MSS Window
irtt Iface
172.16.3.0 0.0.0.0 255.255.255.0 U 40 0
0 eth1
172.16.65.0 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
0.0.0.0 172.16.65.240 0.0.0.0 UG 40 0
0 eth0
nameserver 172.16.65.240
domain
search

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