Juniper JUNOSE 11.2.X IP SERVICES, Configuration Manual

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Inside Local Addresses
The inside local address is a configured IP address that is assigned to a host on the inside
network. Addresses may be globally unique (not requiring translation), allocated from
the private address space defined in RFC 1918, or officially allocated to some other
organization.
Inside Global Addresses
The inside global address is the translated IP address of an inside host as seen by an
outside host and network. Addresses may be allocated from a globally unique address
space (often provided by the ISP, if the inside address is connected to the global Internet).
Outside Local Addresses
The outside local address is the translated IP address of an outside host as it appears to
the inside network. Addresses may be globally unique (not requiring translation), allocated
from the private address space defined in RFC 1918, or officially allocated to some other
organization.
Outside Global Addresses
The outside global address is the configured, publicly routable IP address assigned to a
host on the outside network.
Understanding Address Translation
Address translation can occur one of two ways: inside or outside source translation.
Inside Source Translation
Inside source translation is the most commonly used NAT configuration. When an inside
host sends a packet to the outside network, the NAT router translates the source
information (either the source address or the source address/port pair) and, in the inbound
direction, restores the original information (this time operating on the destination address
or address/port pair).
For outbound traffic, the NAT router translates the inside local address (or address/port)
into the inside global address (or address/port), either through a statically defined
translation or dynamically created translation. For inbound traffic, a translation must be
found to revert the inside global address (or address/port) into the inside local address
(or address/port), or the packet is not routed into the inside network.
NOTE: Dynamic inside source translations are established by outbound traffic.
You use inside source translation in traditional and bidirectional NAT configurations.
Outside Source Translation
Outside source translation is used in NAT configurations only when addresses of external
hosts might create a conflict on the private network. This complementary translation
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Chapter 2: Configuring NAT