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.
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
