NAME

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

SYNOPSIS

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

DESCRIPTION

       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, 203.97.2.0/24 would be removed if 203.97.0.0/17 was
       also supplied.

       The second optimisation identifies adjacent prefixes that can be combined under a single,  shorter-length
       prefix.   For   example,  203.97.2.0/24  and  203.97.3.0/24  can  be  combined  into  the  single  prefix
       203.97.2.0/23.

OPTIONS

       -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
              203.97.2.226/24 would  be  truncated  to  203.97.2.0/24.  Without  this  option  an  input  prefix
              203.97.2.226/24  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.

DIAGNOSTICS

       Aggregate exits 0 on success, and >0 if an error occurs.

EXAMPLES

       The following list of prefixes:

         193.58.204.0/22
         193.58.208.0/22
         193.193.160.0/22
         193.193.168.0/22
         193.243.164.0/22
         194.126.128.0/22
         194.126.132.0/22
         194.126.134.0/23
         194.151.128.0/19
         195.42.240.0/21
         195.240.0.0/16
         195.241.0.0/16

       is optimised as followed by aggregate (output shown using the -v flag):

         aggregate: maximum prefix length permitted will be 24
         [    0] + 193.58.204.0/21
         [    1] - 193.58.204.0/22
         [    2] - 193.58.208.0/22
         [    3]   193.193.160.0/22
         [    4]   193.193.168.0/22
         [    5]   193.243.164.0/22
         [    0] + 194.126.128.0/21
         [    6] - 194.126.128.0/22
         [    7] - 194.126.132.0/22
         [    8] - 194.126.134.0/23
         [    9]   194.151.128.0/19
         [   10]   195.42.240.0/21
         [    0] + 195.240.0.0/15
         [   11] - 195.240.0.0/16
         [   12] - 195.241.0.0/16

       Note  that 193.58.204.0/22 and 193.58.208.0/22 were combined under the single prefix 193.58.204.0/21, and
       194.126.134.0/23 was suppressed because it  was  included  in  194.126.132.0/22.  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:

         193.58.204.0/21
         193.193.160.0/22
         193.193.168.0/22
         193.243.164.0/22
         194.126.128.0/21
         194.151.128.0/19
         195.42.240.0/21
         195.240.0.0/15

SEE ALSO

       aggregate-ios(1)

HISTORY

       Aggregate was written by Joe Abley <jabley@mfnx.net>, 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 <michael.shields@mfn.com>.  The -t option was suggested by
       Robin Johnson <robbat2@fermi.orbis-terrarum.net>, and the treatment of leading zeros on octet parsing was
       changed following comments from Arnold Nipper <arnold@nipper.de>.

       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
       <rnoland@2hip.net>).

BUGS

       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.