Re: tcpdump and <nop,nop,timestamp xxx yyy>
Gerold Jury (jury@173-grips.sime.com)
Mon, 23 Mar 1998 09:14:41 +0100
David S. Miller wrote:
>
> Date: Fri, 20 Mar 1998 22:30:44 -0700 (MST)
> From: Chris Noe <stiker@northlink.com>
>
> Just noticed this while tcpdump'ing a recent telnet (over ppp) session:
>
> 17:30:10.799810 209.75.160.90.1025 > 209.75.160.32.telnet: S 3310621889:3310621889(0) win 32488 <mss 536,nop,nop,timestamp 112754 0,wscale 0,eol> (DF)
> 17:30:10.976449 209.75.160.32.telnet > 209.75.160.90.1025: S 1854400001:1854400001(0) ack 3310621890 win 16768 <mss 1460,nop,wscale 0,nop,nop,timestamp 17611 112754>
>
> ...
>
> What are these <nop,nop>'s doing before my timestamps?
> Could they be affecting throughput? (two in *each* packet sent/recv'd)
>
I've noticed them too and after checking the sources i found
/proc/sys/net/ipv4/tcp_timestamps and
/proc/sys/net/ipv4/tcp_window_scaling
which default to 1 for testing purposes.
tcp_window_scaling however gives my router ( KA9Q NOS version 2.16 ) a
headache.
That means somehow it doesn't understand the SYN packets and drops them
silently.
Maybe it could save time for some people if this makes it into the
documentation
(ip-sysctl.txt).
greetings
Gerold Jury
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