aggregate6 - a fast versatile prefix list compressor

Job Snijders job at
Thu Nov 30 20:27:34 UTC 2017

Someone suggested I should clarify what 'aggregate6' actually does :-)

aggregate6 takes a list of IPv4 and/or IPv6 prefixes in conventional
format, 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, 2001:67c:208c:10::/64 would be removed if
2001:67c:208c::/48 was also supplied.

The second optimisation identifies adjacent prefixes that can be
combined under a single, shorter-length prefix. For example,
2001:67c:208c::/48 and 2001:67c:208d::/48 can be combined into the
single prefix 2001:67c:208c::/47. As an IPv4 exampl: and can be joined into

The above two optimalisations are useful in context of firewall rule
generation or generation of BGP prefix-list filters.

Kind regards,


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