Network Access using AX.25 over IP or UDP

The AX/25 protocol can be carried by IP (Internet Protocol) or UDP (User Datagram Protocol). This enables AX.25 tunnels to be created wherever IP connectivity exists. This access method is primarily used for BBS-to-BBS forwarding.

AX.25 over IP or UDP can be used to access the following SCCo ARES/RACES network service:

• Packet BBS Service
  • BBS Forwarding: Other packet BBSs can connect to the SCCo BBS network using AX.25 over (i.e. inside of) an IP or UDP tunnel. The AMPRnet uses AXIP tunnels. Individual BBS-to-BBS forwarding links can use AXIP or AXUDP, depending on the capabilities of the two BBSs on the link.

• Establish an AX.25 link
  • AMPRnet is preferred
    • All SCCo packet BBSs are already connected to the AMPRnet using standard AX.25 over IP (AXIP) tunnels to all other AMPRnet gateways. Hostnames are as follows:
      • W1XSC: w1xsc.ampr.org
      • W2XSC: w2xsc.ampr.org
      • W3XSC: w3xsc.ampr.org
      • W4XSC: w4xsc.ampr.org
      • W5XSC: w5xsc.ampr.org
      • W6XSC: w6xsc.ampr.org
  • Individual BBS-to-BBS forwarding links
    • For BBSs which are not already connected to the AMPRnet, individual AX.25 over IP (AXIP) or AX.25 over UDP (AXUDP) tunnels can be created.
• Establish a forwarding schedule
  • Select what will be forwarded
    • Select whether mail to the call sign of the BBS should be forwarded or not
      • Some BBS sysops prefer to not have mail to the BBS's call sign forwarded so they can more easily perform remote testing
    • Select the bulletin distributions you wish to receive. You may want no bulletins. Or, depending on your location, you may wish to receive one or more of the following:
      • bay - San Francisco and Monterey Bay Area
      • nca - Northern California
      • ca - California
      • wusa - Western USA
      • usa - United States
      • noam - North America (USA, Canada, Mexico, ...)
      • ww - Worldwide
  • Agree to a forwarding schedule
    • For BBSs in Northern California, we typically prefer once or twice per hour
    • For all other BBSs, we typically prefer no more than once an hour

• AX.25 over IP or UDP Tunnel Station Configuration Diagram (PDF)
• BBS or node capable of AXIP or AXUDP connections
• Network connection
  • For networking only with SCCo BBSs:
    • Intranet connection to SCCo ARES/RACES network
  • For general AMPRnet access:
    • Internet connection that allows either AXIP or AXUDP connections.
      • Note: Typical consumer Internet services often do not allow AXIP.
• Recommended: Firewall to block all but specific AXIP or AXUDP connections

Technical Reference

• AXIP
  • AX.25 over IP (IP Protocol 93)
  • Least overhead; preferable if IP protocol 93 can be passed through firewalls
  • RFC 1226: Internet Protocol Encapsulation of AX.25 Frames
• AXUDP
  • AX.25 over UDP
  • Essentially the same as AXIP, except that instead of placing the AX.25 frames directly in an IP packet (which requires a new protocol number), it places the AX.25 frames in a UDP packet.
  • Typically used where IP protocol 93 is not allowed (such as some consumer Internet Service providers)
  • Adds overhead of UDP layer (which is irrelevant at megabit speeds)
  • UDP port numbers are selected and agreed upon by endpoints of the connection

User Groups