=head1 NAME

ipv6 - IPv6 support in MRTG

=head1 OVERVIEW

MRTG and cfgmaker support SNMP over IPv6. IPv6 targets can be specified by
hostname or IPv6 address, and if the required libraries are present (see
below), queries will use IPv6.

=head1 USAGE

=head2 Enabling IPv6

IPv6 is currently disabled by default and must be explicitly enabled. In
MRTG this is done by turning on the B<EnableIPv6> global option in the
configuration file. In cfgmaker, it is enabled with the B<--enable-ipv6>
command-line option.

If IPv6 is disabled, MRTG and cfgmaker should behave in exactly the same way
as previous versions. So the addition of IPv6 support should have no effect
on existing MRTG setups unless IPv6 is enabled.

IPv6 support requires the Socket6 and INET6 libraries (see below). If MRTG
can't find them, IPv6 is disabled.

=head2 Specifying IPv6 targets

IPv6 targets may be specified by name or IPv6 address. Numeric IPv6 addresses
may be used with both cfgmaker and MRTG, but they must be enclosed in square
brackets.

For example, a target could be specified as:

 public@[2001:760:4::]:161

Hostnames work as expected: first an IPv6 name lookup is tried, then an IPv4
lookup.

=head2 Targets that do not support SNMP over IPv6

Many targets (this currently includes all Cisco routers) do not yet support
SNMP over IPv6 and must be monitored over IPv4. This can cause problems if
you specify a target through its DNS name and the name maps to both the IPv6
address and the IPv4 address of the target: MRTG will only try IPv6, and will
fail.

To query these targets, use the B<IPv4Only> per-target option, which tells
MRTG not to use SNMP over IPv6 for the target.

MRTG does not fall back to IPv4 for performance and correctness reasons. If
there are many routers to query, a timeout for every router would make MRTG
take too long to query them all. And if, for some reason, IPv6 connectivity to
the target is lost, MRTG's error messages can help figure out what is wrong.

cfgmaker does fall back from IPv6 to IPv4. If IPv6 is enabled and cfgmaker is
given a hostname that resolves to both an IPv6 and an IPv4 address, it first
tries to query the target over IPv6. If it receives no answer, it tries again
using IPv4. If the target answers, cfgmaker sets the IPv4Only option in the
generated config file.

=head1 IPv6 LIBRARIES

=head2 Libraries required

IPv6 support requires the B<Socket6> and B<INET6> Perl modules. Both can be
downloaded from CPAN:

http://search.cpan.org/author/UMEMOTO/Socket6/

http://search.cpan.org/author/MONDEJAR/INET6/

If you use Debian, you will need the packages B<libsocket6-perl> and
B<libio-socket-inet6-perl>, which are (or should soon be) in unstable.

So far, IPv6 support has been tested on Linux only, and only with Socket6
version 0.12. Also note that IPv6 won't work at all if you don't have
INET6.pm version 2.00 or newer.

=head2 Installing the libraries

Building and installing Socket6 and INET6 is very simple. For each module,
just unpack the archive and then do:

 perl Makefile.PL
 make

and then:

 su
 make install

If you have installed the libraries successfully, cfgmaker and mrtg should
automatically detect them and allow IPv6 support to be enabled.
