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Re: Issue 223: Event-Timestamp and Duplicate Detection
Bernard Aboba wrote:
> However, if an Event-Timestamp attribute is included in a request, then
> the Identifier will change on retransmission, and this technique will
> not work.
> RFC 2869 Section 5.3, appears to prohibit inclusion of Event-Timestamp
> except in an Accounting-Request:
> RFC 2869 Section 5.19 does not include a table row for the
> Event-Timestamp attribute, suggesting that Event-Timestamp is prohibited
> in Access-Request, Accept, Reject and Challenge packets.
That sounds good.
> However, RFC 3576 suggested inclusion of an Event-Timestamp attribute in
> CoA and Disconnect messages for replay protection. Since the
> Event-Timestamp attribute will change on retransmission of a CoA-Request
> or Disconnect-Request, the Identifier will also change, and this implies
> that duplicates would potentially go undetected. Could this cause a
> I do not think so. If one Disconnect-Request arrives and is responded
> to, then the user has been disconnected (or not) and receiving another
> duplicate request will not make a difference, since you can't disconnect
> a user twice. Similarly, if a CoA-Request was already processed,
> processing it again will yield the same result.
So long as there are no race conditions (login, disconnect, login,
duplicate disconnect), that would appear to be OK.
A longer term fix would be to require Access-Request packets to
contain a Acct-Session-Id attribute, which would be used to detect
duplicate sessions, independent of duplicate packets. That fix would
also mean that EAP may not need the State attribute, as discussed in the
Isses & Fixes draft.
> Still, the Nonce attribute described in RFC 3576bis does not have this
> issue, because the Nonce doesn't change if the packet is retransmitted.
> Would it be a good idea to remove mention of Event-Timestamp from RFC
I would agree. Optional parts of the protocol that could cause
problems are best left umentioned.
> Also, would it be a good idea to include language similar to RFC 2865 in
> RFC 3576bis, such as:
> The NAS can detect a duplicate CoA or Disconnect-Request if
> it has the same server source IP address and source UDP port and
> Identifier within a short span of time.
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