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

[Toke Høiland-Jørgensen]

Dave Taht <dave.taht at gmail.com> writes:

> On Tue, Sep 3, 2019 at 5:23 AM Mikael Abrahamsson <swmike at 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.

-Toke