Blocking TCP flows?

Thu Jun 13 21:11:51 UTC 2013

Are you trying to block flows from becoming established, knowing what
you're looking for ahead of time, or are you looking to examine a
stream of flow establishments, and will snipe off some flows once
you've determined that they should be blocked?

If you know a 5-tuple (src/dst IP, IP protocol, src/dst L4 ports) you
want to block ahead of time, just place an ACL. It depends on the
platform, but those that implement them in hardware can filter a lot
of traffic very quickly.
However, they're not a great tool when you want to dynamically
reconfigure the rules.

For high-touch inspection, I'd recommend a stripe of Linux boxes, with
traffic being ECMP-balanced across all of them, sitting in-line on the
traffic path. It adds a tiny bit of latency, but can scale up to
process large traffic paths and apply complex inspections on the
traffic.

Cheers,
jof

On Thu, Jun 13, 2013 at 12:32 PM, Eric Wustrow <ewust at umich.edu> wrote:
> Hi all,
>
> I'm looking for a way to block individual TCP flows (5-tuple) on a 1-10 gbps
> link, with new blocked flows being dropped within a millisecond or so of
> being
> added. I've been looking into using OpenFlow on an HP Procurve, but I don't
> know much in this area, so I'm looking for better alternatives.
>
> Ideally, such a device would add minimal latency (many/expandable CAM
> entries?), can handle many programatically added flows (hundreds per
> second),
> and would be deployable in a production network (fails in bypass mode). Are
> there any
> COTS devices I should be looking at? Or is the market for this all under
> the table to
> pro-censorship governments?
>
> Thanks,
>
> -Eric