Re: CARD: Storing sequence numbers in ARs' CAR table?

Hi Marco,

On Fri, 10 Oct 2003, Marco Liebsch wrote:

> "...Should the sequence number be stored in CAR table to enforce ordering
> of CARD replies ?"
>
> In my opinion, an AR needs to remember the sequence number
> of a request only until the associated reply can be sent.
> What could be the advantage of maintaining the sequence
> number in an AR's CAR table for a longer time? Info flow
> is from AR->MN, so it's the MN's responsibility to choose
> sequence numbers appropriately for correlating replies
> with requests and possibly to counteract replay attacks.
> In case there is a positive offset in sequence numbers between
> two consecutive Requests, this should not matter, or?

AR also receives piggybacked and other unsolicited AR-AR replies from
other ARs. For these to have ordering, AR should IMO store the sequence
number from the AR-AR CARD message header it receives. Then the sequence
number in CARD request and reply could be used just for matching the
messages.

There is a similar problem is in the MN-AR protocol, with the ordering of
solicited and unsolicited replies. A new field in the MN-AR CARD message
header is _probably_ needed for sequence number, if strict ordering is a
requirement.

Henrik