[PLUG] Red Hat routing follies

[Derek Loree]

On Sun, 2003-10-26 at 19:21, Carla Schroder wrote:
> I have two NICs installed in one of my test boxes. Currently I'm messing 
> around with Red Hat 9. The NICs are common DLink and Linksys, all duly 
> recognized & drivers installed at installation. I'm using only one of them, 
> the box connects to a gateway/firewall/switch unit. The IP of the gateway is 
> 192.168.1.1
> 
> The weird part is I can't figure out how Red Hat determines which one to use. 
> They are configured the same:
> 
> eth0
> DEVICE=eth0
> ONBOOT=yes
> BROADCAST=192.168.1.255
> IPADDR=192.168.1.6
> NETMASK=255.255.255.0
> GATEWAY=192.168.1.1
> 
> eth1
> DEVICE=eth1
> ONBOOT=yes
> BROADCAST=192.168.1.255
> IPADDR=192.168.1.8
> NETMASK=255.255.255.0
> GATEWAY=192.168.1.1
> 
>  The first time I booted it up, I had eth1 connected. But I couldn't get a 
> network connection until I moved the cable to eth0. Now RH has decided it 
> will use eth1.  How?

Well, it just ain't natural to run two interfaces on the same network. 
My guess is that it is a race condition for the default route.  Which
ever one wins the race gets to keep the route, sorta thing.  You should
be able to fix it with a "route add" command. Something like

route add -net 192.168.1.0 netmask 255.255.255.0 gw 192.168.1.1 dev eth0

should force things to go the way you want them to.
> 
> This looks weird too:
> 
> % /sbin/route
> 
> Destination	Gateway	Genmask		Flags	Metric	Ref	Use	Iface
> 192.168.1.0		*	255.255.255.0	U		0		0	0	eth1
> 192.168.1.0		*	255.255.255.0	U		0		0	0	eth1
> 169.254.0.0		*	255.255.0.0	U		0		0	0	eth1
> 127.0.0.0			*	255.0.0.0		U		0		0	0	lo
> default				192.168.1.1	UG		0		0	0	eth1
> 
> Wut the heck is going on here? How did eth1 get all the goodies? where did 
> 169.254.0.0 come from?

I think this is the address space that Winblows boxes use if they can't
find a DHCP server.  RedHat must be making it easier to find them.
> 
> signed, dazed and confused

If you set one of your cards to have no gateway, the other will always
do the routing for you.

HTH,

Derek Loree