Re: SIOCDELRT, or: proper syntax to delete default route for an interface?

[Sven Hartge <sven@svenhartge.de>]

Matt Ventura <mattventura@mattventura.net> wrote:
>> me@client:~$ date ; sudo route -n

>> Thu Jan 22 11:48:48 EST 2015
>> Kernel IP routing table

>> Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
>> 0.0.0.0         10.144.15.100   128.0.0.0       UG    1      0        0 ppp0
>> 0.0.0.0         192.168.1.1     0.0.0.0         UG    0      0        0 eth0
>> 10.144.0.1      0.0.0.0         255.255.255.255 UH    0      0        0 ppp0
>> 128.0.0.0       10.144.15.100   128.0.0.0       UG    1      0        0 ppp0
>> 134.67.15.30    10.8.0.5        255.255.255.255 UGH   1      0        0 tun0

> Try it with 0.0.0.0 instead of default. I didn't notice that the netmask 
> was 128.0.0.0 rather than 0.0.0.0. Not sure why it would do that or if 
> that has some kind of special meaning.

VPN clients normally use two routes as "default" route:

0.0.0.0/128.0.0.0    (or 0.0.0.0/1)
128.0.0.0/128.0.0.0  (or 128.0.0.0/1)

This way, the VPN client does not need to replace the existing default
route. Because those two new route are more specific than 0/0, all
packages are routed into the tunnel and not to the old default gateway.

If the VPN client crashes (or the tunnel interfaces is removed) those
two routes are automatically removed too and the old default route is
active again.

If the client replaced the old default route then you would be left with
a system without any default route, because the new one would have been
deleted together with the tunnel interface.

Grüße,
Sven.

-- 
Sigmentation fault. Core dumped.