Re: wireless + wired + dhcp +... : unproper default route

[Jerome BENOIT <jgmbenoit@wanadoo.fr>]

Thanks for your reply.

Matt Foster wrote:
> Quoting Jerome BENOIT (jgmbenoit@wanadoo.fr):
>
> > Thanks for your reply: fellowing the below advice
> > I wrote an adquate script that I put in the directory
> > /etc/network/if-post-down.d
> > to set a default route when it is missing:
> >
> > route add default gw <default ip>
> >
> > According to the man page we can specify the Iface,
> > instead to let the kernel to chose for us,
> > by adding something as `dev eth0':
> > I have tried it, but each time
> > the default route seems to be blocked after a while
> > (except when I set the kernel favorite Iface).
> >
> > My basic idea was to write after some basic checks:
> >
> > route del default
> > route add default gw <default ip> dev <fastest connected iface>
> >
> > but as I sait I got into troubles:
> >
> > I guess I missed something:
> > any idea ?
> >
> > Thanks in advance,
> > Jerome
>
>
> This may just be me being dense,

I was asking for a hint.

Please note that I am not (yet) familiar with network stuff.

> but why the 'if-post-down.d' directory, as
> opposed to the 'if-up.d' directory? Surely it would be more logical to
> change the routing tables when a new interface comes up? 

in my /etc/network/interface I wrote

iface eth0 inet dhcp

iface wlan0 inet dhcp
  wireless_<option> <value>

so the routing table is managed by the dhcp manchinerie.
This work fine when only one iface is involved,
but troubles emerge when the two ifaces are involved.
For the post-down why, please see below.


> What kind of troubles ddi you have with the route exactly? 
Up to now I encoutered two cases:
1]
my wireless iface (wlan0) and my wired iface (eth0) are plugged
(my automation scheme used ifplugd): I can do basic stuff.
Now if the iface that hold the default route is unplugged,
then the default route is removed by ifdown (called by ifplugd).
In other words I have no more default route,
hence my post-down action to set up the default route
(when the other card is still present):

route add default gw <default ip>

This just mimics what /etc/dhcp3/dhclient-script does.
And it works.

2]
My second point is that the choice of the default route iface
is done by the kernel since the above command contains no `dev' option.
So as my wired connection is far faster than my wireless connection,
I want the eth0 iface as my default interface when possible:
to do so, I try the fellowing:

route del default
route add default gw <default ip> dev eth0

and to check the routing table:

ping ping.symantec.com

If the default iface was eth0 before the `del' action,
the  pinging is ok;
but if the default was `wlan0',
the pinging is ok for a short time,
and then it is lost.

Note that for my wlan0 iface, I have to used the fresh ndiswrapper 
driver, so may be the trouble come from there.

Thanks,
Jerome