\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