1. RADIUS UDP Transport Mapping Avi Lior Bridgewater avi@bridgewatersystems.com avi@bridgewatersystems.com Systems http://www.ietf.org/internet-drafts/draft-lior-radius-udp-transport-mapping- 00.txt

2. Motivation  Improve the reliability of RADIUS protocol. RADIUS uses UDP. RADIUS does not provide guidelines how do to reliable packet transmissions: Retransmit Failover  At this time we only address Retransmit Behavior.

3. Scenarios that Trigger Retransmits  The packet or the response packet was actually dropped by the network. Retransmitting is OK.  The packet was delayed by the network due to congestion. Retransmitting is really Bad.  No response was received because the server is no longer alive. Retransmitting is Bad.  No response was received because the server is congested. The reply is delayed. Retransmitting is really Bad.  No response was received because the packet was silently discarded due to errors. Rare (excluding DOS attacks)

4. Current Practice  Implementations have been using static retransmit timer Manually tuned for a network – but in many cases use the default setting. But static timers may lead to Congestive Collapse of the network.  Implementers retransmit at intermediate nodes.

5. What we recommend  Retransmit at the NAS(ideally) or its Local Proxy. Generally don’t retransmit at intermediary nodes. But you need to keep track at intermediaries because you need to use this information in making failover decisions.  Use Dynamic Retransmit Timeout (RTO) RTO based on RFC 2988 which uses RTT. Track RTO for each destination not the next hop proxy. Difficult because we don’t always know the criteria used to route packets at proxy servers.

6. Additional Recommendation  Add a heartbeat command to RADIUS Can be used by the sender to ascertain whether or not the Next Hop is up or not. Backwards compatible with existing RADIUS protocol. It doesn’t break existing protocol. The sender can determine whether or not the next hop supports this feature.

7. Open Issues  To Jitter or not to Jitter? Always, never or in certain cases.  Differentiated treatment of different packets Access Request Packets Accounting Starts/Stops Accounting Interims. Do we even want to retransmit these?  RTO Initial time is 3 seconds? Minimum is 1 second? Max 60 seconds?

8. Whats next?  Add as work group item?