Subject: Re: [Tsvwg] TCP Question: Reuse of TCB's in time-wait state:

From: "sanjay kaniyar" <[email-masked]>
Date: Thu, 25 Oct 2001 19:33:32 -0700

>It seems like your ISNreverse = snd_next + 128K is intended to avoid

That's right. This is going to protect it in the other direction. The RFC 
does not take this into account.

>this problem, however, the entire sequence space could have been in
>flight (and then some).

I don't see how. If it is assumed that ISN and sequence numbers do not wrap 
around within 2MSL (if a connection indeed wraps around, it should use 
timestamps anyway, in which case I may choose not restore it), this won't 
break.

>It seems like you'd have to ensure that both ends of the connection have
>  ISNs _AND_ timestamps which are valid for restarting. Restoring a
>TIME_WAIT state can, at best, ensure this only for the side that kept
>the TIME_WAIT.

It may not be possible to ensure this with the time-stamps, but it is 
clearly possible to verify this for ISN. If you disagree, an example to 
demonstrate this would be helpful.

Thanks,
Sanjay

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From: Joe Touch <[email-masked]>
Date: Fri, 26 Oct 2001 10:00:22 -0700

sanjay kaniyar wrote:

 > That's right. This is going to protect it in the other direction. The
 > RFC does not take this into account.
 >
 > I don't see how. If it is assumed that ISN and sequence numbers do not
 > wrap around within 2MSL (if a connection indeed wraps around, it should
 > use timestamps anyway, in which case I may choose not restore it), this
 > won't break.

OK - so, since you have to protect BOTH directions (or you shouldn't 
accept the connection), you can't run where timestamps are used.

The only goal here is to reuse a port number pair between two hosts; 
since that implies a very fast connection, unless EVERY connection knows 
that it is short _when it opens_, timestamps will be used.

When then would this solution be useful?

Joe