Filename: 118-multiple-orports.txt
Title: Advertising multiple ORPorts at once
Version: $Revision$
Last-Modified: $Date$
Author: Nick Mathewson
Created: 09-Jul-2007
Status: Needs-Research

Some notes follow. Please feel free to flesh them out, discard them,
add in better ideas, etc.

  - Some way to configure which address:port combinations to listen
    on, and/or which to advertise.

    (The best way to support lots of ports is to have your firewall
    route all connections from those ports to Tor: this doesn't need
    anywhere near as many listening sockets.  You only really want to
    listen on tons and tons of ports if your firewalling doesn't
    support this, or you don't have access to your local
    iptables/ipf/whatever.  But if you want to do this with the
    firewall, you need the ability to advertise ports you aren't
    actually listening on.)

    (Cat would also like to see some discussion of the effect this
    is likely to have in environments that need to ban or limit Tor.
    "Speaking only for myself, in an environment where I need to keep
    a lid on Tor usage, having to chase port settings around makes it
    more likely that I'm going to move from limiting Tor to just plain
    banning it.")

  - Some way to advertise in one's router descriptor which
    address:port combinations you're listening on.  For backward
    compatibility this should be a new line, not a change to the
    format of an existing line.

  - Possibly, some way to relay this information in network-status
    documents.

  - Some analysis of the impact on network-status and routerinfo
    size.  My guess is "not much", but if it turns out to be a bit, we
    should look into making the notation concise.

  - What does this imply for self-testing of servers and testing by
    authorities of servers?  What should the authorities do if one
    addr:port works but one doesn't?

  - Some way to pick which addr:port to use when you have a choice of
    more than one addr:port.

  - Some way to avoid having servers open lots and lots of connections
    between them when they get extend cells to the same server on
    different ports.

    - Suggested rule:
      - If we're told to extend to IP:Port:ID, and we have a connection
        to some server with ID, and we have confirmed that the server
        likes the address we originally used when connecting to it (via
        means in proposal 105), then use the existing connection.
      - If we're told to extend to IP:Port:ID, and we have a descriptor
        for the ID, and we have a connection to some server with ID,
        and the existing connection is to an address listed as valid
        in the descriptor, then use the existing connection.
      - Otherwise, use a new connection.

  - How this all interacts with coderman's ipv6 stuff (proposal 117).