# Trying to block TCP timestamp request.

**URL:** <https://forums.suse.com/t/trying-to-block-tcp-timestamp-request/21968>\
**Category:** SLES Networking\
**Created:** [November 22, 2011, 1:16am UTC](https://forums.suse.com/t/trying-to-block-tcp-timestamp-request/21968 "2011-11-22T01:16:01Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![System1](https://avatars.discourse-cdn.com/v4/letter/s/51bf81/32.png) [@System1](https://forums.suse.com/u/System1)\
**Post date:** [November 22, 2011, 1:16am UTC](https://forums.suse.com/t/trying-to-block-tcp-timestamp-request/21968/1 "2011-11-22T01:16:01Z")

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Hi,

I am trying to block the tcp timestamp request by adding  
net.ipv4.tcp\_timestamps = 0 to /etc/sysctl.conf and reboot. However, it  
does not seem to work. The system still accepting tcp timestamp request  
and replying to it.

sysctl -a | grep timestamp  
net.ipv4.tcp\_timestamps = 0

cat /proc/sys/net/ipv4/tcp\_timestamps  
0

using this tool to do tcp timestamp request ( hping3 --tcp-timestamp  
HOST\_IP )

Thanks

–Guang

## – guangsu

guangsu’s Profile: [http://forums.novell.com/member.php?userid=64346](http://forums.novell.com/member.php?userid=64346)  
View this thread: [http://forums.novell.com/showthread.php?t=448534](http://forums.novell.com/showthread.php?t=448534)

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<div class="post-metadata">

**Author:** ![system](https://us1.discourse-cdn.com/flex022/uploads/suse/original/2X/5/5012ba89e3ffb5220dac47d5ea0ba032e2fe1cb6.png) [@system](https://forums.suse.com/u/system)\
**Post date:** [November 22, 2011, 1:36am UTC](https://forums.suse.com/t/trying-to-block-tcp-timestamp-request/21968/2 "2011-11-22T01:36:00Z")

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On Mon, 21 Nov 2011 23:16:01 GMT  
guangsu [guangsu@no-mx.forums.novell.com](mailto:guangsu@no-mx.forums.novell.com) wrote:  
[color=blue]

> Hi,
> 
> I am trying to block the tcp timestamp request by adding  
> net.ipv4.tcp\_timestamps = 0 to /etc/sysctl.conf and reboot. However,  
> it does not seem to work. The system still accepting tcp timestamp  
> request and replying to it.
> 
> sysctl -a | grep timestamp  
> net.ipv4.tcp\_timestamps = 0
> 
> cat /proc/sys/net/ipv4/tcp\_timestamps  
> 0
> 
> using this tool to do tcp timestamp request ( hping3 --tcp-timestamp  
> HOST\_IP )
> 
> Thanks
> 
> –Guang
> 
> [/color]  
> Hi  
> You probably need to add some iptables rules;  
> [http://blog.theroux.ca/security/disable-tcp-timestamps-on-linux/](http://blog.theroux.ca/security/disable-tcp-timestamps-on-linux/)

–  
Cheers Malcolm °¿° (Linux Counter #276890)  
openSUSE 11.4 (x86\_64) Kernel 2.6.37.6-0.9-desktop  
up 5 days 3:00, 5 users, load average: 0.02, 0.04, 0.05  
GPU GeForce 8600 GTS Silent - Driver Version: 285.05.09