What is really port triggering?

Discussion in 'Wireless Internet' started by Rim, Oct 6, 2003.

  1. Rim

    Rim Guest

    I've read many messages on usenet and I still don't get what port
    triggering is about. I have a LinkSys BEFSR41. I do understand port

    computer 1 on LAN A --> Internet --> firewall (LinkSys) --> computer 2
    on LAN B

    Suppose computer 2 runs a http server, the firewall will have port 80
    forwarded to computer 2 so computer 1 can connect and surf the pages
    on computer 2. That's port forwarding.

    Now suppose computer 2 wants to *ftp* a file, I don't need to setup
    anything other than Stateful Packet Inspection (SPI) and the router
    will 'remember' to send the ftp traffic back to computer 2 when the
    ftp server, somewhere on the internet, replies.

    So what do I really need port triggering for if SPI can always
    remember which of my computers initiated a connection? Why do I need
    port triggering for CUSeeME and not for other services like ftp or

    Rim, Oct 6, 2003
    1. Advertisements

  2. On 6 Oct 2003 04:27:27 -0700, Rim spoketh
    Port triggering is conditional, dynamic port forwarding. If certain
    conditions are met (the trigger), then the specified port(s) will be
    opened for inbound connections to the computer that initiated the
    outbound connection.

    On the befsr41 series of routers, SPI breaks all port forwards and port
    triggers, in addition to making the router very unstable (possibly due
    to lack of memory).

    Lars M. Hansen
    Lars M. Hansen, Oct 6, 2003
    1. Advertisements

  3. Rim

    Duane Arnold Guest

    (Rim) wrote in @posting.google.com:

    Port forwarding means to me is that port(s) are forwarded to an
    IP/machine, because an application at the IP/machine needs the ports
    open. This also means that no other IP/machine can share the ports being
    forwarded. Port forwarding is static.

    As per an application basis such as a Internet game being played by
    multiple IP(s)/machines on your network, port triggering allows multiple
    machines running the same application using the same ports to share the
    ports. The application triggers the router to open the ports and the
    router forwards the traffic to the machine that solicited the inbound
    traffic. Port triggering is dynamic. Port triggering is also used for an
    application such as AOL or MSN Voice Chat.

    To me, the main purpose of SPI on the router is to ensure that for every
    inbound packet to the router, there was a corresponding outbound packet
    sent from a machine behind the router, otherwise, the inbound packet is
    dropped by the router -- state fullness.

    The router doesn't need SPI to know from what machine packets came from
    and to what machine the packets are to go to on the inbound.

    Duane :)
    Duane Arnold, Oct 7, 2003
    1. Advertisements

Ask a Question

Want to reply to this thread or ask your own question?

You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.