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: 10.0.0.0/24 and 10.0.1.0/24 can be joined into 10.0.0.0/23. The above two optimalisations are useful in context of firewall rule generation or generation of BGP prefix-list filters. Kind regards, Job