Bug 152094

Summary:	init.d/net bombs when DHCP gateway is on different subnet to the IP
Product:	Gentoo Linux	Reporter:	Adam Nielsen <a.nielsen>
Component:	[OLD] baselayout	Assignee:	Gentoo's Team for Core System packages <base-system>
Status:	RESOLVED WONTFIX
Severity:	normal
Priority:	High
Version:	2006.0
Hardware:	All
OS:	Linux
Whiteboard:
Package list:		Runtime testing required:	---
Attachments:	Patch to allow a gateway in a different subnet to the IP in a DHCP response

Description Adam Nielsen 2006-10-20 05:02:00 UTC

For Internet access, I configure my ethernet interface via DHCP, and the DHCP response comes from the DSL modem plugged into that NIC.  Unfortunately the DSL modem must be configured as a gateway, but its IP (10.1.1.1) is always on a different subnet to the IP address in the DHCP response, e.g.

My Internet IP: 1.2.3.4
Interface Subnet: 1.2.3.0/24
Default gateway: 10.1.1.1

I get an error because the default gateway is on an unknown subnet:

$ /etc/init.d/net.inet0 restart
 * Stopping inet0
 *   Bringing down inet0
 *     Stopping dhclient on inet0 ...    [ ok ]
 *     Shutting down inet0 ...           [ ok ]
 * Starting inet0
 *   Bringing up inet0
 *     dhcp
 *       Running dhclient ...
PREINIT
deconfig
REBOOT
bound
SIOCADDRT: Network is unreachable

If I add dhcp_inet0="nogateway" to /etc/conf.d/net then the problem goes away - but of course then I don't have a default subnet so no Internet access.

This is the behaviour with at least two different DSL modems supplied by a large Australian ISP.

The scripts really need to check the gateway's subnet, and if it's different to the main IP address, do something like this first:

$ route add -net 10.1.1.0/24 dev inet0

Then later on when the script tries to add the default route the kernel can find the subnet and allows the route to be added.

Comment 1 Adam Nielsen 2006-10-20 18:21:19 UTC

Created attachment 100114 [details, diff]
Patch to allow a gateway in a different subnet to the IP in a DHCP response

This patch (hopefully) applies to /lib/rcscripts/net.modules.d/helpers.d/udhcpc-ifconfig and if a DHCP response is received with a gateway on an unknown subnet, it adds a host route telling the kernel that the gateway is available on the same interface that DHCP is being performed on.

This fixes the bug for me, and should not otherwise affect the behaviour of the script.

Comment 2 Roy Marples (RETIRED) gentoo-dev

2006-10-21 05:08:35 UTC

We let the dhcp clients use their own scripts starting with baselayout-1.12 which is now stable. Basically we punted the entire helpers.d directory from baselayout.

If /sbin/dhclient-script still has your issue then please re-open this bug - hopefully with a patch for it :)