netdev - empty ack packets

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Date:	Fri, 10 Sep 2010 01:12:44 -0400
From:	MK <stardust496@...il.com>
To:	netdev@...r.kernel.org
Subject: empty ack packets

Hello list,

I am looking at a tcpdump and I see that very very frequently, after
receiving a segment, my tcp is sending an empty ack back in a matter
of several (around 20 - 50) microseconds. And then after several more
microseconds, my tcp is sending some valid outgoing data. I am trying
to understand why it decided to send an empty ack back when that ack
could potentially have been delayed by microseconds and get
piggybacked on the outgoing data.

>From the code, it appears that the delayed ack timeout is 40 millisecs
so it is likely not the delack timer that is causing this. (And I do
not have the quickack option)

This is RHEL5 (2.6.18) kernel.

Does anybody have an idea as to what is happening?

Thanks a lot!!
--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html