aggregate - optimise a list of route prefixes to help make nice short
aggregate [-m max-length] [-o max-opt-length] [-p default-length] [-q]
Takes a list of prefixes in conventional format on stdin, and performs
two optimisations to attempt to reduce the length of the prefix list.
The first optimisation is to remove any supplied prefixes which are
superfluous because they are already included in another supplied
prefix. For example, 184.108.40.206/24 would be removed if 220.127.116.11/17
was also supplied.
The second optimisation identifies adjacent prefixes that can be
combined under a single, shorter-length prefix. For example,
18.104.22.168/24 and 22.214.171.124/24 can be combined into the single prefix
Sets the maximum prefix length for entries read from stdin
max_length bits. The default is 32. Prefixes with longer lengths
will be discarded prior to processing.
Sets the maximum prefix length for optimisation to max-opt-
length bits. The default is 32. Prefixes with longer lengths
will not be subject to optimisation.
Sets the default prefix length. There is no default; without
this option a prefix without a mask length is treated as
invalid. Use -p 32 -m 32 -o 32 to aggregate a list of host
routes specified as bare addresses, for example.
-q Sets quiet mode -- instructs aggregate never to generate warning
messages or other output on stderr.
-t Silently truncate prefixes that seem to have an inconsistent
prefix: e.g. an input prefix 126.96.36.199/24 would be truncated
to 188.8.131.52/24. Without this option an input prefix
184.108.40.206/24 would not be accepted, and a warning about the
inconsistent mask would be generated.
-v Sets verbose mode. This changes the output format to display the
source line number that the prefix was obtained from, together
with a preceding "-" to indicate a route that can be suppressed,
or a "+" to indicate a shorter-prefix aggregate that was added
by aggregate as an adjacency optimisation. Note that verbose
output continues even if -q is selected.
Aggregate exits 0 on success, and >0 if an error occurs.
The following list of prefixes:
is optimised as followed by aggregate (output shown using the -v flag):
aggregate: maximum prefix length permitted will be 24
[ 0] + 220.127.116.11/21
[ 1] - 18.104.22.168/22
[ 2] - 22.214.171.124/22
[ 3] 126.96.36.199/22
[ 4] 188.8.131.52/22
[ 5] 184.108.40.206/22
[ 0] + 220.127.116.11/21
[ 6] - 18.104.22.168/22
[ 7] - 22.214.171.124/22
[ 8] - 126.96.36.199/23
[ 9] 188.8.131.52/19
[ 10] 184.108.40.206/21
[ 0] + 220.127.116.11/15
[ 11] - 18.104.22.168/16
[ 12] - 22.214.171.124/16
Note that 126.96.36.199/22 and 188.8.131.52/22 were combined under the
single prefix 184.108.40.206/21, and 220.127.116.11/23 was suppressed
because it was included in 18.104.22.168/22. The number in square
brackets at the beginning of each line indicates the original line
number, or zero for new prefixes that were introduced by aggregate.
The output without the -v flag is as follows:
Aggregate was written by Joe Abley <email@example.com>, and has been
reasonably well tested. It is suitable for reducing customer prefix
filters for production use without extensive hand-proving of results.
Autoconf bits were donated by Michael Shields
<firstname.lastname@example.org>. The -t option was suggested by Robin
Johnson <email@example.com>, and the treatment of
leading zeros on octet parsing was changed following comments from
Arnold Nipper <firstname.lastname@example.org>.
An early version of aggregate would attempt to combine adjacent
prefixes regardless of whether the first prefix lay on an appropriate
bit boundary or not (pointed out with great restraint by Robert Noland
Common unix parsing of IPv4 addresses understands the representation of
individual octets in octal or hexadecimal, following a "0" or "0x"
prefix, respectively. That convention has been deliberately disabled
here, since resources such as the IRR do not follow the convention, and
confusion can result.
For extremely sensitive applications, judicious use of the -v option
together with a pencil and paper is probably advisable.