session recovery on change of IP

[John Sutton]

On Fri, 11 Apr 2003, David Woodhouse wrote:
> On Fri, 2003-04-11 at 12:50, John Sutton wrote:
> > Is it possible to configure ssh so that a session can continue/recover
> > after a change of IP?
> 
> man screen
> 
> Other than that, no.

I can't see how using screen gets me any further?  Surely screen just
allows multiple sessions multiplexed into one tty stream (badly put but
I think I know what I mean ;-).  End result will be that *all* the
sessions get broken on a change of IP?  

> > Any solution?
> 
> Avoid changing the IP address you use for the connection, by tunnelling
> from your dynamic dialup address to somewhere else, and effectively
> giving yourself a static IP address?

This is an intriguing notion... Markus Friedl (see other post) has
suggested the same.  I have limited experience with tunnelling protocols
(I messed around with pptp bewteen linux and windoze boxes some years ago)
but I can't immediately see how this could work.  Surely to set up an IP
tunnel of any sort you have got to have two "fixed" endpoints?

OTOH, I can see how you *might* have a "lightweight, non-encrypted"
tunnelling protocol which *is* impervious to change of IP.  Then you could
run an ssh session through this tunnel.  Quite how the server end of the
tunnel would recognise that this "new" connection was actually an existing
connection which had changed it's IP and therefore be able to tie the 2
ends back together, I don't know...

Does this make any sense?

> This is being sent from an unmetered static IP dialup in the UK though.
> Not that it's not expensive, mind you :)

How expensive is that?  The minimum I've found is £51+vat per month (for
300 hours per month) single channel ISDN.  I consider this *too* expensive
so I've gone back to using a dynamic dialup for £11+vat ;-(

***************************************************
John Sutton
SCL Internet
URL http://www.scl.co.uk/
Tel. +44 (0) 1239 711 888
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