Re: [Cerowrt-devel] [Bloat] talking at linux plumbers in portugal next week

[Dave Taht <dave.taht@gmail.com>]

On Tue, Sep 3, 2019 at 7:45 AM Toke Høiland-Jørgensen <toke@toke.dk> wrote:
>
> Dave Taht <dave.taht@gmail.com> writes:
>
> > On Tue, Sep 3, 2019 at 5:23 AM Mikael Abrahamsson <swmike@swm.pp.se> wrote:
> >>
> >> On Mon, 2 Sep 2019, Dave Taht wrote:
> >>
> >> > with copy-pasted parameters set in the 90s - openwrt's default, last I
> >> > looked, was 25/sec.
> >>
> >> -A syn_flood -p tcp -m tcp --tcp-flags FIN,SYN,RST,ACK SYN -m limit --limit 25/sec --limit-burst 50 -m comment --comment "!fw3" -j RETURN
> >> -A syn_flood -m comment --comment "!fw3" -j DROP
> >>
> >> Well, it's got a burst-size of 50. I agree that this is quite
> >> conservative.
> >>
> >> However, at least in my home we're not seeing drops:
> >>
> >> # iptables -nvL | grep -A 4 "Chain syn_flood"
> >> Chain syn_flood (1 references)
> >>   pkts bytes target     prot opt in     out     source               destination
> >>   2296  113K RETURN     tcp  --  *      *       0.0.0.0/0            0.0.0.0/0            tcp flags:0x17/0x02 limit: avg 25/sec burst 50 /* !fw3 */
> >>      0     0 DROP       all  --  *      *       0.0.0.0/0            0.0.0.0/0            /* !fw3 */
> >>
> >> But you might be right that in places with a lot more clients then this
> >> might indeed cause problems.
> >
> > Well, *I* long ago had upped those params by 10x and don't see syn
> > drops either on my backbone. But I rather suspect the rest of the
> > world just copy-pasted it. It should scale as a function of bandwidth,
> > I suppose, or get updated as a side effect of setting QoS - or just
> > get bumped up. Start a bug over with openwrt? Take a hard look at
> > other firewall designs?
>
> FWIW:
>
> # iptables -nvL syn_flood
> Chain syn_flood (1 references)
>  pkts bytes target     prot opt in     out     source               destination
>  195K   12M RETURN     tcp  --  *      *       0.0.0.0/0            0.0.0.0/0            tcp flags:0x17/0x02 limit: avg 25/sec burst 50 /* !fw3 */
>     0     0 DROP       all  --  *      *       0.0.0.0/0            0.0.0.0/0            /* !fw3 */
>
> # ip6tables -nvL syn_flood
> Chain syn_flood (1 references)
>  pkts bytes target     prot opt in     out     source               destination
>   396 41508 RETURN     tcp      *      *       ::/0                 ::/0                 tcp flags:0x17/0x02 limit: avg 25/sec burst 50 /* !fw3 */
>     0     0 DROP       all      *      *       ::/0                 ::/0                 /* !fw3 */
>
> rebooted this box today; don't seem to have hit the limit thus far,
> though... This is on a gigabit link.

Hmm. Try to trigger it with --te=upload_streams=200 ?

>
> -Toke



-- 

Dave Täht
CTO, TekLibre, LLC
http://www.teklibre.com
Tel: 1-831-205-9740