[Snort-devel] Stream5: Missing TCP connections with require_3whs

Steven Sturges steve.sturges at ...402...
Thu Jan 8 10:54:05 EST 2009

Thanks, Lothar.

We'll have a look... Since ECN and CWR are technically experimental,
it would be good to get a feel for how many people are actually
seeing those used in TCP or IP headers on their networks?

We'd welcome some insights -- what routers support congestion
notification and control?  IPv4 and/or IPv6?


Lothar Braun wrote:
> Hi all,
> I noticed that snort- does not recognize all possible TCP
> connections when require_3whs is enabled for the Stream5 preprocessor.
> A connection is missed if the TCP-Handshake packets (especially the
> SYN-Pakets) have the ECN- or CWR-Flag set. This is due to stream5 only
> checking for p->tcph->th_flags == TH_SYN, which is false if TH_SYN
> _and_ TH_ECN are set.
> I've created a patch against snort- (see attachment) that fixes
> the problem.
> Best regards,
>   Lothar
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