| \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" or "\fIN\fP bytes per seconds" (see below for some examples). |
| .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 either as |
| a number, with an optional time quantum suffix (the default is 3/hour), or as |
| \fIamount\fPb/second (number of bytes per second). |
| .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. When byte-based rate matching is requested, this option specifies |
| the amount of bytes that can exceed the given rate. This option should be used |
| with caution -- if the entry expires, the burst value is reset too. |
| .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. |
| .TP |
| \fB\-\-hashlimit\-rate\-match\fP |
| Classify the flow instead of rate-limiting it. This acts like a |
| true/false match on whether the rate is above/below a certain number |
| .TP |
| \fB\-\-hashlimit\-rate\-interval\fP \fIsec\fP |
| Can be used with \-\-hashlimit\-rate\-match to specify the interval |
| at which the rate should be sampled |
| .PP |
| Examples: |
| .TP |
| matching on source host |
| "1000 packets per second for every host in 192.168.0.0/16" => |
| \-s 192.168.0.0/16 \-\-hashlimit\-mode srcip \-\-hashlimit\-upto 1000/sec |
| .TP |
| matching on source port |
| "100 packets per second for every service of 192.168.1.1" => |
| \-s 192.168.1.1 \-\-hashlimit\-mode srcport \-\-hashlimit\-upto 100/sec |
| .TP |
| matching on subnet |
| "10000 packets per minute for every /28 subnet (groups of 8 addresses) |
| in 10.0.0.0/8" => |
| \-s 10.0.0.0/8 \-\-hashlimit\-mask 28 \-\-hashlimit\-upto 10000/min |
| .TP |
| matching bytes per second |
| "flows exceeding 512kbyte/s" => |
| \-\-hashlimit-mode srcip,dstip,srcport,dstport \-\-hashlimit\-above 512kb/s |
| .TP |
| matching bytes per second |
| "hosts that exceed 512kbyte/s, but permit up to 1Megabytes without matching" |
| \-\-hashlimit-mode dstip \-\-hashlimit\-above 512kb/s \-\-hashlimit-burst 1mb |