Re: gateway is missing

[Gary Thomas <gary@mlbassoc.com>]

On 2014-03-24 14:45, Niklas Molin wrote:
> Hi.
> 
> I'm trying to toggle the eth0 with ifconfig
> I noticed that it I couldn't access my board after that.
> After some more testing it seems like I can't access my board from a different subnetwork.
> So I did a route -nee (before and after eth0 down and up) and it seems lie the gateway is gone.
> 
> root@imx6qsabresd:~# route -nee
> Destination     Gateway         Genmask         Flags   MSS Window  irtt Iface
> 0.0.0.0         192.168.55.1    0.0.0.0         UG        0 0          0 eth0
> 192.168.55.0    0.0.0.0         255.255.255.0   U         0 0          0 eth0
> root@imx6qsabresd:~# ifconfig eth0 down
> root@imx6qsabresd:~# ifconfig eth0 up  
> 
> When link is back:
> root@imx6qsabresd:~# route -nee
> Kernel IP routing table
> Destination     Gateway         Genmask         Flags   MSS Window  irtt Iface
> 192.168.55.0    0.0.0.0         255.255.255.0   U         0 0          0 eth0
> 
> I did this on a SabreSD and also my custom board.
> 
> Is there anything I'm missing in my setup?

When you run 'ifconfig eth0 down', not only is that interface marked
as 'down', but all routes which are based on it are deleted.  When you
bring it back up with 'ifconfig eth0 up', the system has no idea that
you need any additional routing, etc.  (In fact, it can't make any
assumptions about this at all).

I suspect that your interface (eth0) was originally brought up when
the system booted.  To keep the same behaviour, you'll need to use
the same mechanism as that.

Try this:
  # /etc/init.d/networking restart

Alternatively, you should use different commands to take the interface up/down.
Use 'ifdown eth0' instead of 'ifconfig eth0 down'
    'ifup eth0' instead of 'ifconfig eth0 up'
These commands will respect the setup you have in /etc/network/interfaces where
the raw 'ifconfig' commands do not.

-- 
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Gary Thomas                 |  Consulting for the
MLB Associates              |    Embedded world
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