универсальный 32-битный фильтр управления трафиком (universal 32bit traffic control filter)
VALUES
Options and selectors require values to be specified in a
specific format, which is often non-intuitive. Therefore the
terminals in SYNOPSIS have been given descriptive names to
indicate the required format and/or maximum allowed numeric
value: Prefixes u32, u16 and u8 indicate four, two and single
byte unsigned values. E.g. u16 indicates a two byte-sized value
in range between 0 and 65535 (0xFFFF) inclusive. A prefix of int
indicates a four byte signed value. A middle part of _hex_
indicates that the value is parsed in hexadecimal format.
Otherwise, the value's base is automatically detected, i.e.
values prefixed with 0x are considered hexadecimal, a leading 0
indicates octal format and decimal format otherwise. There are
some values with special formatting as well: ip_address and
netmask are in dotted-quad formatting as usual for IPv4
addresses. An ip6_address is specified in common, colon-separated
hexadecimal format. Finally, prefixlen is an unsigned, decimal
integer value in range from 0 to the address width in bits (32
for IPv4 and 128 for IPv6).
Sometimes values need to be dividable by a certain number. In
that case a name of the form N*val was chosen, indicating that
val must be dividable by N. Or the other way around: the
resulting value must be a multiple of N.
