© Tony Lawrence, aplawrence.com
How can I print to a remote PC that does not have a static IP address?
This is a fairly common problem: you have a PC at home and you make some sort of connection over the internet to your server, but your application needs to print to your PC. That would be easier if your PC had a fixed, constant IP address, but your connection is dynamic so it changes.
By the way: this article assumes a Unix/Linux server. It doesn't talk about Windows apps, though often the solution is exactly the same concept.
There are many, many ways to solve this problem. So many, in fact. that I'll probably miss one or two in this write up. If I do miss something, do let me know: it may help someone else down the line.
Some of these methods involve configuring an LPD printer on your remote Windows machine. That's easy to do with Windows 2000 or XP and Windows LPD clients are easily found for other versions. A Google search for "Windows LPD Server" will turn up hundreds of options, free and low cost. The concept here is that you define an lpd printer on the server, and that its address will be looked up by name.. somewhere. Some of these even help you do that automatically, usually by way of something running on the server that their software can contact. Some things you might want to look at in this area include:
- Tarantella http://www.tarantella.com ("follow me printing" is what they call it)
- FacetWin http://www.facetcorp.com
- ICE-TCP http://www.jriver.com (it's the "ice.lp" part you want;
Other ways to do this are to use Windows SMB style printing. That will require Visionfs, Samba or FacetWin on the server and some help for those to "find" the connecting PC. Personally, I like the LPD solutions better, but in some situations the SMB way can be easy enough.
- Dynamic DNS services
Register a domain name and subscribe to a dynamic dns service. There are dozens of them: Google search for "dynamic dns service" and pick what you like. A little client runs on your Windows machine and updates the service whenever your IP changes. When the server goes looking for "xyz.com", the dynamic dns service tells it what your address is now.
This approach can work, though it also has its problems. The issue, especially with the free and inexpensive services, is that they may be slow or inaccurate in updating, which will kill you dead for printing.
- Write your own DNS update client/server
This really isn't hard to do in Perl. The idea is to have a little client on the Windows PC that probably runs at boot, figures out its IP address, and contacts a matching server app on your server to inform the system of your new address. Keep in mind that thw Windows side doesn't need to try to figure out its address (and may not even know it if it's going through a firewall); when it contacts the server, the server will be able to tell where it came from. You could even do this using a "port knocking" technique (see What is "port knocking"?) where you'd log the attempt to access some port and then scan the logs to pick up the address.
See Dynamic DNS Services for examples of writing your own update scripts.
- Use "local printing"
Local printing comes from old dumb terminals that, with the proper escape codes, would then send all data received out another port until a "stop local print" code was received. See http://aplawrence.com/Unixart/terminals.html for more on that. Windows terminal emulators can often be set to respond to the same codes and send the data to your Windows printer.
Your application may make this a reasonable choice, or it may be more difficult than you may like. Most terminal emulators (see What are some terminal emulators I can use from windows? and http://www.anzio.com/support/whitepapers/printguide.htm) support this.
- Use a VPN connection
Appliance VPN's are very inexpensive; for example see http://aplawrence.com/Reviews/rf550vpn.html. Most of these can happily work with the remote side using DHCP, and can also provide DHCP to the network (which may be only 1 machine if remote). With a VPN, your address will (or can be) fixed as far as the other side of the VPN is concerned: you are always 192.168.4.2 for example. See http://aplawrence.com/Basics/vpn.html if you don't understand that yet.
- Manual methods
If you have root access to the machine you are using, just do a "su" and edit /etc/hosts. You can get your address from "who -mux", from netstat -a and all sorts of other ways: see How do I find out what IP address a user logged in from?
- Scripting it automatically.
Have something run from the user's .profile that finds out the address and updates /etc/hosts (or DNS).
The problem here is that you need root access to update /etc/hosts. There are three ways to solve that:
- You might use sudo: see http://aplawrence.com/Basics/sudo.html or (OSR5) "asroot" or (Unixware) "tfadmin and adminuser"
- Make a setuid binary that runs the script.
- Use a named pipe: the unprivileged client writes to the pipe, a root owned process reads from it.
Some sample scripts for that are shown below.
# remotelpsetup, run at boot (run in background!) /etc/fuser -k /dev/remoteprinters /bin/rm -f /dev/remoteprinters /etc/mknod /dev/remoteprinters p while true do exec < /dev/remoteprinters /usr/local/bin/updateremotelp done
# pickprinter, called from user's .profile set `/bin/who -mxu` MYTTY=$2 MYADD=$6 MYALREADY=`grep $MYADD /etc/hosts| sed 's/ .*//'` if [ "$MYALREADY" ] then MYADD=$MYALREADY fi test -z "$MYADD" && exit 0 case $MYTTY in ttyp[0-9]*) :;; *) exit 0; esac case $MYADD in -) exit 0;; 192.168.*) exit 0;; localhost) exit 0;; *) : ;; esac while true do echo "Please select the printer you wish to use 1. Tiffany 2. Marilyn 3. Amelia 4. Susan Q. Quit " PRINTER="" read choice case $choice in 1) PRINTER=TIFFANY;; 2) PRINTER=MARILYN;; 3) PRINTER=AMELIA;; 4) PRINTER=SUSAN;; [qQ]) exit 0;; esac if test -z "$PRINTER" then : else echo "CookieM $PRINTER $MYADD" > /dev/remoteprinters echo "Printer $PRINTER set for $MYADD" exit 0; fi done
# updateremote read key printer address case $key in CookieM) : ;; *) exit 0;; esac /bin/grep -v $address /etc/hosts > /tmp/hosts.$$ /bin/grep -v $printer //tmp/hosts.$$ > /tmp/hosts2.$$ echo "$address\t$printer" >> /tmp/hosts2.$$ cp /tmp/hosts2.$$ /etc/hosts /bin/rm /tmp/hosts.$$
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