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Re: Blocking TCP flows?
From: Phil Fagan <philfagan () gmail com>
Date: Thu, 13 Jun 2013 16:37:57 -0600

I really like the idea of a stripe of linux boxes doing the heavy lifting.
Any suggestions on platforms, card types, and chip types that might be
better purposed at processing this type of data?

I assume you could write some fast Perl to ingest and manage the tables?
What would the package of choice be for something like this?

On Thu, Jun 13, 2013 at 3:11 PM, Jonathan Lassoff <jof () thejof com> wrote:

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


On Thu, Jun 13, 2013 at 12:32 PM, Eric Wustrow <ewust () umich edu> wrote:
Hi all,

I'm looking for a way to block individual TCP flows (5-tuple) on a 1-10
link, with new blocked flows being dropped within a millisecond or so of
added. I've been looking into using OpenFlow on an HP Procurve, but I
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
and would be deployable in a production network (fails in bypass mode).
there any
COTS devices I should be looking at? Or is the market for this all under
the table to
pro-censorship governments?



Phil Fagan
Denver, CO

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