Installing printer across 2 networks

Posted on 2010-01-04
Last Modified: 2012-08-13
We just setup 2 networks, the main and remote side, each on a different subnet.  They are directly connected by 2 routers going across a laser.  Everything seems to work fine except for the static printers.  I have a printer on the remote side and it's install on the printer server on the main side.  I can print to it fine on the main side but not even install it on the remote side.  I cannot add any of the static printers on the remote side.  I can add smaller dhcp printer fines.  I can ping the printer from both sides by ip and name.  It works if I install the printer as a local printer, but not as a network printer on the remote side.  Any ideas how to add it as a network printer from the printer server from the main side.
Question by:durango099
    LVL 5

    Accepted Solution

    There are 2 parts for answer: network part and setting up printer part. Gateway, hereafter, means not the cheap SoHo off-the-shelf routers; it means manually configurable ones like Cisco or Linux or BSD gateways.

    For the network part, lets say there are gw-A and printer-A in subnet A and gw-B and node-B in subnet B. node-B tries to print to printer-A. printer-A has gw-A as gateway and properly set up IP address but it does not have any ARP entry matched to any IP address in subnet B (and you as an admin cannot put in any static route in printer's host routing table). Here is what happen:

    1) node-B prints to printer-A. The packet goes to gw-B which in turn, forwards it to printer-B. gw-B has interfaces in both subnets

    2) printer-A replies but when it does, it looks at source IP and finds that it is not in the same broadcast domain. So printer-A sends the packet to its default gateway, gw-A. gw-A has, for i.e, an interface in Internet and in subnet A.

    3) gw-A, upon receiving given-up packet from printer-A, consults its routing table and finds that gateway for destination net is gw-B and forwards the packet to gw-B. This is critical point. gw-A CANNOT modify packet's source or destination IP (using for i.e SNAT/DNAT in iptables or nat/rdr in pf) or else the packet will be dropped. So how does it forward to gw-B without IP? Using ARP address of gw-B! If you are still vague, google on ARP IP interactions.
    gw-A will also send icmp redirect to printer-A saying a better route is via gw-B. Due to this, printer-A will send directly to gw-B in the future (until its ARP entry expires).
    Not only your firewall rules need to allow given-up packet but also allow that packet and subsequent packets to go back out of the same interface to gw-B
    If you are stuck at this point, there are only 2 most likely causes. One is your firewall rules on gw-A are dropping this given-up packet or you have disabled icmp redirects on gw-A. To troubleshoot, run tcpdump at gw-A interface to subnet A.

    4) gw-B will then forward the packet to node-B. Viola, everybody's happy!

    5) Btw, alternative solution to this network part is to enable NAT on gw-B's subnet A interface. Then, you won't have to deal with this troubleshooting mess. But there are some disadvantages to this approach.

    Here is the printer part! This seemingly easy part took out a couple of hours from me. There are 3 ways to set up printer in Windows: local, network, via http.

    1) If you try to set up via network, it WON'T work. Why? That network setup assumes one broadcast domain (a.k.a one subnet). Even if you use printer software that comes with printer, the same assumption applies

    2) Via http? It will work (in my case) only if you have print server in front of the printer. The printer will connect to print server which will connect to the network. This case is not considered since I don't have print server.

    3) Normally, people think of local as printer has to be physically attached. Only partially correct. This is the correct way to set up a printer located in different subnet. In Windows XP, go to Add Printer > Local printer (uncheck auto-detect box) > Create A New Port > Select TCP/IP > [Next] > Type in IP address and follow the rest of instructions to load the driver.
    LVL 1

    Author Comment

    I expected more than a copy and paste from a search.  So there is no way to setup the printer via network across 2 subnets?  We have a temp fix, we installed the printer as a local printer on a workstation on the remote side and shared it, so that subnet can use it.  Any other ideas would be helpful, but would like to make it work from the print server without installing IIS to use http method.
    LVL 5

    Expert Comment

    if you can ping it, then create on your computer a TCP/IP port for that printer then, try using it, i will setup that environment here to mimic your situation and then try to print

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