The "quota2" implements a named counter which can be increased or decreased on a per-match basis. Available modes are packet counting or byte counting. The value of the counter can be read and reset through procfs, thereby making this match a minimalist accounting tool.

When counting down from the initial quota, the counter will stop at 0 and the match will return false, just like the original "quota" match. In growing (upcounting) mode, it will always return true.

--grow
    Count upwards instead of downwards.

--no-change
    Makes it so the counter or quota amount is never changed by packets matching this rule. This is only really useful in "quota" mode, as it will allow you to use complex prerouting rules in association with the quota system, without counting a packet twice.

--name name
    Assign the counter a specific name. This option must be present, as an empty name is not allowed. Names starting with a dot or names containing a slash are prohibited.

[!] --quota iq
    Specify the initial quota for this counter. If the counter already exists, it is not reset. An "!" may be used to invert the result of the match. The negation has no effect when --grow is used.

--packets
    Count packets instead of bytes that passed the quota2 match.

Because counters in quota2 can be shared, you can combine them for various purposes, for example, a bytebucket filter that only lets as much traffic go out as has come in:

-A INPUT -p tcp --dport 6881 -m quota --name bt --grow; -A OUTPUT -p tcp --sport 6881 -m quota --name bt;