Subject: Re: Anomalous TCP behaviour?

From: der Mouse <[email-masked]>
Date: Tue, 25 Jan 2000 10:15:25 -0500 (EST)

> Is it normal for TCP to skip a certain number of bytes and send them
> later when it receives dup acks?

No.  Without knowing where this tcpdump was taken I can't be sure what
the cause is, but this looks a whole lot like dropped packets - on the
sending system, on the receiving system, or anywhere in between, as
long as it's before the tcpdump point.

> ## Also it is obvious from the tcpdump o/p that the Fast retransmit
> mechanism doesnt get kicked off after 3 dup acks - is this normal
> behaviour?

Maybe.  Fast retransmit could be happening; all we know is that
*tcpdump* doesn't see the retransmit before it sees the other acks.
Again, it depends heavily on the network characteristics.  If you're
sniffing close to the receiving host, and there's relatively high
latency between the two principals, this behavior would not surprise me
at all.

					der Mouse

			       [email-masked]
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From: Mark Allman <[email-masked]>
Date: Tue, 25 Jan 2000 11:39:00 -0500

> i think the address is [email-masked]... where did you get
> this address? 

We changed domain names (from "lerc.nasa.gov" to "grc.nasa.gov").
Both still work, however the GRC form is preferred (as the LeRC form
may not work at some point).

allman