VPN disconnect

VPN disconnect

[tony.chamberlain]

This is another VPN question.

We have a regular IP address which we use to connect to a PPTP VPN
which assigns us 10.0.1.29.  If the PPTP connection goes down, we
will lose that address.

Our software relies on our IP address being 10.0.1.29.  Is there a way,
if the VPN temporarily goes down, to maintain the IP address of
10.0.1.29 ?

Re: VPN disconnect

[James Carlson]

tony.chamberlain@lemko.com writes:
> This is another VPN question.
> 
> We have a regular IP address which we use to connect to a PPTP VPN
> which assigns us 10.0.1.29.  If the PPTP connection goes down, we
> will lose that address.
> 
> Our software relies on our IP address being 10.0.1.29.  Is there a way,
> if the VPN temporarily goes down, to maintain the IP address of
> 10.0.1.29 ?

You can tell pppd to request a particular address by adding it to your
options, like this:

	pppd 10.0.1.29: ipcp-accept-local

(The ":" at the end means "request this local address, and don't
insist on any particular peer address.")

pppd doesn't have an automatic means to save the last-used address for
a link and pick it up again.  Perhaps it should have one, but you
could do this in a script by having your own /etc/ppp/ip-up that
stores $IPREMOTE into a file, and then pull in that file's contents
for a later invocation of pppd.

Note that this just tells pppd to request a particular address.
There's no telling whether the peer understands what to do with such a
request, or if it can or will honor it.  Some servers may refuse to
negotiate at all under such conditions, causing the link to fail.
(Bugs are unfortunately common.)

-- 
James Carlson         42.703N 71.076W         <carlsonj@workingcode.com>

Re: VPN disconnect

[James Cameron]

On Wed, Feb 04, 2009 at 12:11:33PM -0500, James Carlson wrote:
> Note that this just tells pppd to request a particular address.
> There's no telling whether the peer understands what to do with such a
> request, or if it can or will honor it.  Some servers may refuse to
> negotiate at all under such conditions, causing the link to fail.
> (Bugs are unfortunately common.)

On the peer side, pptpd on Linux in the default configuration gives the
IP address to pppd on command line, and so the IP address is usually
non-negotiable.  I don't know about other peers.

-- 
James Cameron                         http://quozl.netrek.org/
HP Open Source, Volunteer             http://opensource.hp.com/
PPTP Client Project, Release Engineer http://pptpclient.sourceforge.net/