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SubjectRe: [PATCH] netfilter: nf_queue: Replace conntrack entry
In Kristian Evensen <> wrote:
> SKBs are assigned a conntrack entry before being passed to any NFQUEUEs,
> and if no entry is found then a new one is created. This behavior causes
> problems for some traffic patterns. For example, if two UDP packets
> to/from the same host (using the same ports) arrive at the "same" time,
> both are assigned a new conntrack entry. After the first packet have
> traversed all chains, the conntrack entry will be inserted into the
> global table. The second packet will then be dropped during the
> insertion step, as an entry for the same flow already exists. One type
> of application that frequently generates this traffic pattern, is DNS
> resolvers.

> This commit introduces a new function that checks, and potentially
> replaces, the conntrack entry for any additional "new" SKBs mapping to
> an existing flow. While not a perfect solution, there are still
> situations where to-be-dropped SKBs can slip through, the situations is
> improved considerably. On the routers I have used for testing, packets
> belonging to the same UDP flow are let through (when generating the
> traffic pattern described above). Without the change in this commit, all
> packets except the first one was dropped.

> With the change in this commit, a user can implement "perfect" solutions
> in user-space. An application can for example keep track of seen UDP
> flows, and then only release packets belonging to one flow when the
> entry has been created. Without the change, and SKB is stuck with the
> original conntrack entry.

Any progress on this patch?

> Signed-off-by: Kristian Evensen <>
> ---
> net/netfilter/nfnetlink_queue.c | 68 +++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 68 insertions(+)


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