1\fBhashlimit\fP uses hash buckets to express a rate limiting match (like the
2\fBlimit\fP match) for a group of connections using a \fBsingle\fP iptables
3rule. Grouping can be done per-hostgroup (source and/or destination address)
4and/or per-port. It gives you the ability to express "\fIN\fP packets per time
5quantum per group" or "\fIN\fP bytes per seconds" (see below for some examples).
6.PP
7A hash limit option (\fB\-\-hashlimit\-upto\fP, \fB\-\-hashlimit\-above\fP) and
8\fB\-\-hashlimit\-name\fP are required.
9.TP
10\fB\-\-hashlimit\-upto\fP \fIamount\fP[\fB/second\fP|\fB/minute\fP|\fB/hour\fP|\fB/day\fP]
11Match if the rate is below or equal to \fIamount\fP/quantum. It is specified either as
12a number, with an optional time quantum suffix (the default is 3/hour), or as
13\fIamount\fPb/second (number of bytes per second).
14.TP
15\fB\-\-hashlimit\-above\fP \fIamount\fP[\fB/second\fP|\fB/minute\fP|\fB/hour\fP|\fB/day\fP]
16Match if the rate is above \fIamount\fP/quantum.
17.TP
18\fB\-\-hashlimit\-burst\fP \fIamount\fP
19Maximum initial number of packets to match: this number gets recharged by one
20every time the limit specified above is not reached, up to this number; the
21default is 5.  When byte-based rate matching is requested, this option specifies
22the amount of bytes that can exceed the given rate.  This option should be used
23with caution -- if the entry expires, the burst value is reset too.
24.TP
25\fB\-\-hashlimit\-mode\fP {\fBsrcip\fP|\fBsrcport\fP|\fBdstip\fP|\fBdstport\fP}\fB,\fP...
26A comma-separated list of objects to take into consideration. If no
27\-\-hashlimit\-mode option is given, hashlimit acts like limit, but at the
28expensive of doing the hash housekeeping.
29.TP
30\fB\-\-hashlimit\-srcmask\fP \fIprefix\fP
31When \-\-hashlimit\-mode srcip is used, all source addresses encountered will be
32grouped according to the given prefix length and the so-created subnet will be
33subject to hashlimit. \fIprefix\fP must be between (inclusive) 0 and 32. Note
34that \-\-hashlimit\-srcmask 0 is basically doing the same thing as not specifying
35srcip for \-\-hashlimit\-mode, but is technically more expensive.
36.TP
37\fB\-\-hashlimit\-dstmask\fP \fIprefix\fP
38Like \-\-hashlimit\-srcmask, but for destination addresses.
39.TP
40\fB\-\-hashlimit\-name\fP \fIfoo\fP
41The name for the /proc/net/ipt_hashlimit/foo entry.
42.TP
43\fB\-\-hashlimit\-htable\-size\fP \fIbuckets\fP
44The number of buckets of the hash table
45.TP
46\fB\-\-hashlimit\-htable\-max\fP \fIentries\fP
47Maximum entries in the hash.
48.TP
49\fB\-\-hashlimit\-htable\-expire\fP \fImsec\fP
50After how many milliseconds do hash entries expire.
51.TP
52\fB\-\-hashlimit\-htable\-gcinterval\fP \fImsec\fP
53How many milliseconds between garbage collection intervals.
54.PP
55Examples:
56.TP
57matching on source host
58"1000 packets per second for every host in 192.168.0.0/16" =>
59\-s 192.168.0.0/16 \-\-hashlimit\-mode srcip \-\-hashlimit\-upto 1000/sec
60.TP
61matching on source port
62"100 packets per second for every service of 192.168.1.1" =>
63\-s 192.168.1.1 \-\-hashlimit\-mode srcport \-\-hashlimit\-upto 100/sec
64.TP
65matching on subnet
66"10000 packets per minute for every /28 subnet (groups of 8 addresses)
67in 10.0.0.0/8" =>
68\-s 10.0.0.8 \-\-hashlimit\-mask 28 \-\-hashlimit\-upto 10000/min
69.TP
70matching bytes per second
71"flows exceeding 512kbyte/s" =>
72\-\-hashlimit-mode srcip,dstip,srcport,dstport \-\-hashlimit\-above 512kb/s
73.TP
74matching bytes per second
75"hosts that exceed 512kbyte/s, but permit up to 1Megabytes without matching"
76\-\-hashlimit-mode dstip \-\-hashlimit\-above 512kb/s \-\-hashlimit-burst 1mb
77