This MIB module extends the IETF draft NAT MIB available at
http://tools.ietf.org/html/draft-ietf-behave-nat-mib-11 
The extensions are intended to address the needs of the Carrier
Grade NAT (CGN), also known as Large Scale NAT (LSN).

GLOSSARY
==========
Address mapping - is used to refer to association between
a private IP to public IP (in case of NAT44 and DS Lite)
or source IPv6 address to IPv4 address in case of NAT64 
stateful application.

Mapping - A mapping used to refer to a NAT translation record.
It is a record held in memory that maps a private IP address
and port to a public IP address and port.

Subscriber - A subscriber is a record held in memory that
provides IP address and other details of an end user device
which has one or more mappings.

Session - A session is a record maintained in memory that
identifies a flow. The flow is uniquely identified by the
source IPv4/IPv6 address, source port, translated IP address,
translated source port, destination IPv4/IPv6 address and
destination port.

In to Out packet - A packet originating from a subscriber,
with a private source address (or with an IPv6 address in
case of NAT64), destined to a host with a public IP address.
This packet needs NAT (or NAPT) service.

Out to In packet - A packet originating from a host on the
public Internet (or any host with a routable/public) source
address, whose destination address is a mapped (translated)
IP address. This packet needs reverse-NAT.

Bulk port allocation - A NAT instance can be configured
pre-allocate a range of contiguous ports instead of a single
port. A mapping log record is created indicating the range of
ports allocated to this subscriber. This is done in anticipation
that the subscriber is likely to send packets that require more
mappings to be created. For the subsequent mapping requests, one
of the pre-allocated port is used and no additional log entries
need to be created. This is a technique used to reduce the
volume of translation record data.