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aggregate - optimise a list of route prefixes to help make nice short filters


aggregate [-m max-length] [-o max-opt-length] [-p default-length] [-q] [-t] [-v]


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, would be
removed if was also supplied.

The second optimisation identifies adjacent prefixes that can be combined under a single,
shorter-length prefix. For example, and can be combined into
the single prefix


-m max-length
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.

-o max-opt-length
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.

-p default-length
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 would be truncated to Without this option an
input prefix 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] +
[ 1] -
[ 2] -
[ 3]
[ 4]
[ 5]
[ 0] +
[ 6] -
[ 7] -
[ 8] -
[ 9]
[ 10]
[ 0] +
[ 11] -
[ 12] -

Note that and were combined under the single prefix, and was suppressed because it was included in 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:

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