NAME
    Mail::SpamAssassin::Plugin::ASN - SpamAssassin plugin to look up the
    Autonomous System Number (ASN) of the connecting IP address.

SYNOPSIS
     loadplugin Mail::SpamAssassin::Plugin::ASN

     asn_lookup asn.routeviews.org _ASN_ _ASNCIDR_
 
     asn_lookup_ipv6 origin6.asn.cymru.com _ASN_ _ASNCIDR_

     add_header all ASN _ASN_ _ASNCIDR_

     header TEST_AS1234 X-ASN =~ /^1234$/

DESCRIPTION
    This plugin uses DNS lookups to the services of an external DNS zone
    such as at "http://www.routeviews.org/" to do the actual work. Please
    make sure that your use of the plugin does not overload their
    infrastructure - this generally means that you should not use this
    plugin in a high-volume environment or that you should use a local
    mirror of the zone (see "ftp://ftp.routeviews.org/dnszones/"). Other
    similar zones may also be used.

TEMPLATE TAGS
    This plugin allows you to create template tags containing the connecting
    IP's AS number and route info for that AS number.

    The default config will add a header field that looks like this:

     X-Spam-ASN: AS24940 213.239.192.0/18

    where "24940" is the ASN and "213.239.192.0/18" is the route announced
    by that ASN where the connecting IP address came from. If the AS
    announces multiple networks (more/less specific), they will all be added
    to the "_ASNCIDR_" tag, separated by spaces, eg:

     X-Spam-ASN: AS1680 89.138.0.0/15 89.139.0.0/16

    Note that the literal "AS" before the ASN in the _ASN_ tag is
    configurable through the *asn_prefix* directive and may be set to an
    empty string.

CONFIGURATION
    The standard ruleset contains a configuration that will add a header
    field containing ASN data to scanned messages. The bayes tokenizer will
    use the added header field for bayes calculations, and thus affect which
    BAYES_* rule will trigger for a particular message.

    Note that in most cases you should not score on the ASN data directly.
    Bayes learning will probably trigger on the _ASNCIDR_ tag, but probably
    not very well on the _ASN_ tag alone.

SEE ALSO
    http://www.routeviews.org/ - all data regarding routing, ASNs, etc....

    http://issues.apache.org/SpamAssassin/show_bug.cgi?id=4770 -
    SpamAssassin Issue #4770 concerning this plugin

STATUS
    No in-depth analysis of the usefulness of bayes tokenization of ASN data
    has been performed.

ADMINISTRATOR SETTINGS
    asn_lookup asn-zone.example.com [ _ASNTAG_ _ASNCIDRTAG_ ]
        Use this to lookup the ASN info in the specified zone for the first
        external IPv4 address and add the AS number to the first specified
        tag and routing info to the second specified tag.

        If no tags are specified the AS number will be added to the _ASN_
        tag and the routing info will be added to the _ASNCIDR_ tag. You
        must specify either none or both of the tag names. Tag names must
        start and end with an underscore.

        If two or more *asn_lookup*s use the same set of template tags, the
        results of their lookups will be appended to each other in the
        template tag values in no particular order. Duplicate results will
        be omitted when combining results. In a similar fashion, you can
        also use the same template tag for both the AS number tag and the
        routing info tag.

        Examples:

          asn_lookup asn.routeviews.org

          asn_lookup asn.routeviews.org _ASN_ _ASNCIDR_
          asn_lookup myview.example.com _MYASN_ _MYASNCIDR_

          asn_lookup asn.routeviews.org _COMBINEDASN_ _COMBINEDASNCIDR_
          asn_lookup myview.example.com _COMBINEDASN_ _COMBINEDASNCIDR_

          asn_lookup in1tag.example.net _ASNDATA_ _ASNDATA_

    asn_lookup_ipv6 asn-zone6.example.com [_ASN_ _ASNCIDR_]
        Use specified zone for lookups of IPv6 addresses. If zone supports
        both IPv4 and IPv6 queries, use both asn_lookup and asn_lookup_ipv6
        for the same zone.

    clear_asn_lookups
        Removes any previously declared *asn_lookup* entries from a list of
        queries.

    asn_prefix 'prefix_string' (default: 'AS')
        The string specified in the argument is prepended to each ASN when
        storing it as a tag. This prefix is rather redundant, but its
        default value 'AS' is kept for backward compatibility with versions
        of SpamAssassin earlier than 3.4.0. A sensible setting is an empty
        string. The argument may be (but need not be) enclosed in single or
        double quotes for clarity.