netdev - Re: [PATCH 1/2] netfilter/xt_hashlimit: new feature/algorithm for xt

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Date:   Mon, 4 Sep 2017 12:14:33 +0200
From:   Pablo Neira Ayuso <pablo@...filter.org>
To:     Vishwanath Pai <vpai@...mai.com>
Cc:     kadlec@...ckhole.kfki.hu, netfilter-devel@...r.kernel.org,
        johunt@...mai.com, fw@...len.de, netdev@...r.kernel.org,
        pai.vishwain@...il.com
Subject: Re: [PATCH 1/2] netfilter/xt_hashlimit: new feature/algorithm for
 xt_hashlimit

On Fri, Aug 18, 2017 at 04:58:59PM -0400, Vishwanath Pai wrote:
[...]
> The main difference between the existing algorithm and the new one is
> that the existing algorithm rate-limits the flow whereas the new
> algorithm does not. Instead it *classifies* the flow based on whether
> it is above or below a certain rate. I will demonstrate this with an
> example below. Let us assume this rule:
> 
> iptables -A INPUT -m hashlimit --hashlimit-above 10/s -j new_chain
> 
> If the packet rate is 15/s, the existing algorithm would ACCEPT 10
> packets every second and send 5 packets to "new_chain".
> 
> But with the new algorithm, as long as the rate of 15/s is sustained,
> all packets will continue to match and every packet is sent to new_chain.

Sounds good, applied, thanks.

A couple of questions: Does it really make sense to expose
--hashlimit-rate-interval or are you using 1 second always there? I
always wonder if it makes sense to expose yet another toggle that it's
not clear to me how the user would take advantage from this.

Just curious here.