[arch-general] Switching between Internet connections

Leonid Isaev lisaev at umail.iu.edu
Fri Dec 7 13:41:56 EST 2012

On Fri, 07 Dec 2012 13:02:12 +0530
Sudaraka Wijesinghe <sudaraka.wijesinghe at gmail.com> wrote:

> Hello,
> My laptop is connected to a LAN with Internet connection and it gets the
> IP stuff (address, routing, dns) via dhcp using the default systemd
> scripts on boot. I also have a 3G modem (USB) which I have created the
> ppp scripts to connect based on the Wiki article
> https://wiki.archlinux.org/index.php/3G_and_GPRS_modems_with_pppd
> Both connections work fine, except after switching to modem from LAN
> some applications (pidgin, xchat, ect. which were running) still uses
> the DNS nameserver from previous connection (LAN) meaning they still
> trying to send DNS queries to LAN router (which is not reachable at that
> time). This gets fixed after that application is closed and reopened.
> Is this behavior normal or a bug?

I think it is normal. If you suspect DNS is the problem, just use a static
resolv.conf with google/comodo dns nameservers (add "nohook resolv.conf"
to /etc/dhcpcd.conf to forbid dhcpcd to touch the file).

> Thanks.
> P.S.
> To disconnect/connect from LAN I either use:
> > # systemctl stop dhcpcd at wlan0
> > # systemctl start dhcpcd at wlan0
> or
> > # dhcpcd -k wlan0
> > # dhcpcd wlan0
> To disconnect/connect I use poff/pon commands and the scripts are setup
> exactly as described on the Wiki.

So, you become root everytime you change network? If you need this kind
of dynamic connectivity, you'll be much better off using networkmanager...

Leonid Isaev
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