\fBhashlimit\fP uses hash buckets to express a rate limiting match (like the \fBlimit\fP match) for a group of connections using a \fBsingle\fP iptables rule. Grouping can be done per-hostgroup (source and/or destination address) and/or per-port. It gives you the ability to express "\fIN\fP packets per time quantum per group": .TP matching on source host "1000 packets per second for every host in 192.168.0.0/16" .TP matching on source port "100 packets per second for every service of 192.168.1.1" .TP matching on subnet "10000 packets per minute for every /28 subnet in 10.0.0.0/8" .PP A hash limit option (\fB\-\-hashlimit\-upto\fP, \fB\-\-hashlimit\-above\fP) and \fB\-\-hashlimit\-name\fP are required. .TP \fB\-\-hashlimit\-upto\fP \fIamount\fP[\fB/second\fP|\fB/minute\fP|\fB/hour\fP|\fB/day\fP] Match if the rate is below or equal to \fIamount\fP/quantum. It is specified as a number, with an optional time quantum suffix; the default is 3/hour. .TP \fB\-\-hashlimit\-above\fP \fIamount\fP[\fB/second\fP|\fB/minute\fP|\fB/hour\fP|\fB/day\fP] Match if the rate is above \fIamount\fP/quantum. .TP \fB\-\-hashlimit\-burst\fP \fIamount\fP Maximum initial number of packets to match: this number gets recharged by one every time the limit specified above is not reached, up to this number; the default is 5. .TP \fB\-\-hashlimit\-mode\fP {\fBsrcip\fP|\fBsrcport\fP|\fBdstip\fP|\fBdstport\fP}\fB,\fP... A comma-separated list of objects to take into consideration. If no \-\-hashlimit\-mode option is given, hashlimit acts like limit, but at the expensive of doing the hash housekeeping. .TP \fB\-\-hashlimit\-srcmask\fP \fIprefix\fP When \-\-hashlimit\-mode srcip is used, all source addresses encountered will be grouped according to the given prefix length and the so-created subnet will be subject to hashlimit. \fIprefix\fP must be between (inclusive) 0 and 32. Note that \-\-hashlimit\-srcmask 0 is basically doing the same thing as not specifying srcip for \-\-hashlimit\-mode, but is technically more expensive. .TP \fB\-\-hashlimit\-dstmask\fP \fIprefix\fP Like \-\-hashlimit\-srcmask, but for destination addresses. .TP \fB\-\-hashlimit\-name\fP \fIfoo\fP The name for the /proc/net/ipt_hashlimit/foo entry. .TP \fB\-\-hashlimit\-htable\-size\fP \fIbuckets\fP The number of buckets of the hash table .TP \fB\-\-hashlimit\-htable\-max\fP \fIentries\fP Maximum entries in the hash. .TP \fB\-\-hashlimit\-htable\-expire\fP \fImsec\fP After how many milliseconds do hash entries expire. .TP \fB\-\-hashlimit\-htable\-gcinterval\fP \fImsec\fP How many milliseconds between garbage collection intervals.