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

From: Jerome BENOIT (jgmbenoit_at_wanadoo.fr)
Date: 12/30/03

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    Date: Tue, 30 Dec 2003 15:29:57 +0200
To: Matt Foster <mattfoster@clara.co.uk>

    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 

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