On 24/11/2020 22:37, ѽ҉ᶬḳ℠ wrote:
On 24/11/2020 23:08, kfm@xxxxxxxxxxxxx wrote:
On 14/11/2020 12:29, ѽ҉ᶬḳ℠ wrote:
host: armv7l GNU/Linux
kernel: 5.10.0-rc3-next-20201113
nftables: v0.9.6
______
this rule in a > inet filter prerouting chain:
icmp type 8 add @b_sa4_lan_pinger { ip saddr limit rate over 2/day }
log flags all prefix "ping_ip4 from LAN > rate_limit_d DROP: " drop;
Having tried different values, e.g.
limit rate over 2/day
limit rate over 44/day
limit rate over 300/day
frames # 1 -5 are always passing through but as of frame count # 6
the frames always being dropped, no matter the x/day value.
That's probably because the default burst value is 5, not that anyone
would know this by reading the nft documentation. The terse
explanation of the limit module in iptables-extensions(8) applies but
there is a better explanation to be found here:
https://www.netfilter.org/documentation/HOWTO/packet-filtering-HOWTO-7.html
Given 2/day, the initial five tokens are being taken from the bucket,
following which no token is added until 12 hours have elapsed. Try
repeating your experiments with the burst value specified as 1.
Documentation aside, it doesn't help that both iptables/xt_limit and
nft/limit fail to report the burst value unless it was explicitly
defined.
Thank you for your valuable thoughts. I am not sure however that the
default bust limit is the cause here, for two reasons:
It explains the cause of the initial five packets being permitted before
running up against any limit. Given 2 as a numerator, try with lower
burst values.
Take "2/min burst 1 packets" as an example. The bucket will have a
capacity of just one token and will be initialised with one upon loading
the ruleset. The bucket will be topped up with one token every 30
seconds, but never beyond its capacity. The result should be that one
packet is allowed to pass at rigid 30 second intervals.
Specifying "2/min burst 2 packets" will result in the bucket being
initialised with - and having a capacity of - two tokens. Within the
first 30 second delta, it will be possible for two packets to pass
before the limit applies. Still, the bucket is topped up at the same
rate of one token every 30 seconds.
the outcome is the same with:
limit rate over 44/day
On average, this should allow for 44 a day by recharging the bucket at a
rate of one token every 24/44*60 = 32.73 minutes.
limit rate over 300/day
In this case, by recharging the bucket at a rate of one token every 4.8
minutes. You would need to run your test case for at least that long to
observe a difference and for at least 24 hours to prove whether or not
the overall rate is maintained.
and should not be however. The other reason is that it should be the
same outcome with limit rate over X/minute but it is not
For the benefit of anyone investigating, could you define a test case
that concretely demonstrates the problem?
A somewhat inconsistent behaviour with x/minute value, e.g.
icmp type 8 add @b_sa4_lan_pinger { ip saddr limit rate over
13/minute } log flags all prefix "ping_ip4 from LAN > rate_limit_d
DROP: " drop;
produces on the client side:
ping -4 -n 20 google.com
Pinging google.com [216.58.208.110] with 32 bytes of data:
Reply from 216.58.208.110: bytes=32 time=14ms TTL=114
Reply from 216.58.208.110: bytes=32 time=15ms TTL=114
Reply from 216.58.208.110: bytes=32 time=14ms TTL=114
Reply from 216.58.208.110: bytes=32 time=18ms TTL=114
Reply from 216.58.208.110: bytes=32 time=18ms TTL=114
Reply from 216.58.208.110: bytes=32 time=13ms TTL=114
Request timed out.
Reply from 216.58.208.110: bytes=32 time=14ms TTL=114
Request timed out.
Reply from 216.58.208.110: bytes=32 time=16ms TTL=114
Request timed out.
Reply from 216.58.208.110: bytes=32 time=16ms TTL=114
Reply from 216.58.208.110: bytes=32 time=13ms TTL=114
Request timed out.
Reply from 216.58.208.110: bytes=32 time=154ms TTL=114
Request timed out.
Reply from 216.58.208.110: bytes=32 time=32ms TTL=114
Reply from 216.58.208.110: bytes=32 time=13ms TTL=114
Request timed out.
Reply from 216.58.208.110: bytes=32 time=14ms TTL=114
Ping statistics for 216.58.208.110:
Packets: Sent = 20, Received = 14, Lost = 6 (30% loss),
Approximate round trip times in milli-seconds:
Minimum = 13ms, Maximum = 154ms, Average = 26ms
Whilst the count is matching the rule it is not clear why not all 13
initial frames are passing through consistently and the excess being
dropped consistently but instead the first being dropped is earlier?
--
Kerin Millar
