Apologies in advance for any operational content this may contain.
I have a customer who wants to get a static ip with his dialup. He uses SSH extensively
and plans to do X11 forwarding, and if he gets disconnected and redials and gets another
IP the previous sessions would be inaccessible.
I can do static IP but I want to try to save the guy a couple bucks.
Would a static IP be required to make sure he doesn't lose those X11 sessions after a disconnect?
Asking here because I figure my chances of getting an accurate answer are better here than on
any of the other mailing lists I read.
Apologies in advance for any operational content this may contain.
I have a customer who wants to get a static ip with his dialup. He
uses SSH extensively and plans to do X11 forwarding, and if he
gets disconnected and redials and gets another IP the previous
sessions would be inaccessible.
I can do static IP but I want to try to save the guy a couple
bucks.
Would a static IP be required to make sure he doesn't lose those
X11 sessions after a disconnect?
Required, but not sufficient.
The TCP stack on each side must remain up continuously. If his TCP
stack resets and he redials, the first packet he gets from the far end
will be met with an RST, and tear down the connection.
The easiest way to do this is to put the modem on a system different
from the SSH endpoint (router, NAT, FW, whatever). If you are using a
NAT or FW in between, it's critical that the state/translation tables
not be flushed when the dial interface goes down/up.
Of course, if you're running TCP or ssh keepalives (or ssh2 rekeying),
and that happens when the link is down, your connection will go away
anyway.
The proper way to do this is with an X analog of screen. VNC is one
possibility. VNC is free, and this would not require a static IP.
Then again, we're talking dialup here. Your customer should do this a
couple of times before he gets dead set on it. Even with LBX and
compression on the SSH session, X over dialup is unpleasant.
Apologies in advance for any operational content this may contain.
I have a customer who wants to get a static ip with his dialup. He uses SSH
extensively
and plans to do X11 forwarding, and if he gets disconnected and redials and
gets another
IP the previous sessions would be inaccessible.
I can do static IP but I want to try to save the guy a couple bucks.
Would a static IP be required to make sure he doesn't lose those X11
sessions after a disconnect?
  No. He just has to be able to request a 'preferred' IP and be granted it if
it's available. DHCP can do this.
  On his end, he must request his last IP as his 'preferred' IP. On your end,
you must give a client the IP they request if it's available.
  If you want to be really slick, you will 'reserve' an IP for 2 minutes after
it's released and only allow it to be reissued (within those two minutes) to
the same user. This protects all your dialup users from session hijacking and
gives them some of the benefits of a static IP while still allowing you to
overcommit IP addresses.
Asking here because I figure my chances of getting an accurate answer are
better here than on
any of the other mailing lists I read.
His best bet would be to use vnc - http://www.uk.research.att.com/vnc/
or one of its variants. Failing that, a pptp connection using RFC1918
addresses for the two endpoints could do the trick, but I'm not sure how
X would deal with the icmp host unreachable messages that would be
received when the pptp session goes down (would probably kill them).
It should also be noted that vanilla vnc is not encrypted (but can be
forwarded over an ssh connection or ssl'ized or <insert your favourite
method here>).
