Jozsef Kadlecsik wrote: > On Fri, 7 May 2010, Pascal Hambourg wrote: > >>> I think what was really meant was tcp_loose, not tcp_be_liberal. >> In my understanding, tcp_loose only allows conntrack to pick up >> connections from the middle, but packets are still INVALID until the >> required number of packets is seen and accepted. Am I wrong ? > > No, the packets are set to the usual states, there's no packet counting. > > With tcp_loose enabled (default) conntrack accepts non-SYN packets as > "NEW" ones, i.e. attempts to pick up connections from the middle. > > With tcp_be_liberal enabled (default is disabled) out of window packets > are not marked as INVALID. I have applied the following patch to the documentation based on this discussion. I have also uploaded a new version of the webpage.
doc: description on how to block traffic with conntrack was incomplete From: Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx> This patch completes the documentation with the following discussion that took place in the mailing list. http://marc.info/?l=netfilter&m=127335152521674&w=2 Signed-off-by: Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx> --- doc/manual/conntrack-tools.tmpl | 9 +++++++-- 1 files changed, 7 insertions(+), 2 deletions(-) diff --git a/doc/manual/conntrack-tools.tmpl b/doc/manual/conntrack-tools.tmpl index b897318..ab4e5fb 100644 --- a/doc/manual/conntrack-tools.tmpl +++ b/doc/manual/conntrack-tools.tmpl @@ -19,7 +19,7 @@ </authorgroup> <copyright> - <year>2008</year> + <year>2008-2010</year> <holder>Pablo Neira Ayuso</holder> </copyright> @@ -198,7 +198,12 @@ conntrack v0.9.7 (conntrack-tools): 1 flow entries have been shown. conntrack v0.9.7 (conntrack-tools): 1 flow entries has been updated. </programlisting> -<para>Delete one entry, this can be used to block traffic (you have to set <emphasis>/proc/sys/net/ipv4/netfilter/ip_conntrack_tcp_be_liberal</emphasis> to zero).</para> +<para>Delete one entry, this can be used to block traffic if:</para> +<itemizedlist> + <listitem><para>You have a stateful rule-set that blocks traffic in INVALID state.</para></listitem> + <listitem><para>You have to set <emphasis>/proc/sys/net/ipv4/netfilter/ip_conntrack_tcp_loose</emphasis> or <emphasis>/proc/sys/net/netfilter/nf_conntrack_tcp_loose</emphasis>, depending on your kernel version, to zero.</para></listitem> +</itemizedlist> + <programlisting> # conntrack -D -p tcp --dport 3486 tcp 6 431982 ESTABLISHED src=192.168.2.100 dst=123.59.27.117 sport=34846 dport=993 packets=169 bytes=14322 src=123.59.27.117 dst=192.168.2.100 sport=993 dport=34846 packets=113 bytes=34787 [ASSURED] mark=1 secmark=0 use=1
