Outside Source Translation; Address Assignment Methods; Static Translations; Dynamic Translations - Juniper JUNOSE SOFTWARE FOR E SERIES 11.3.X - IP SERVICES CONFIGURATION GUIDE 2010-10-01 Configuration Manual

JunosE 11.3.x IP Services Configuration Guide

Outside Source Translation

Address Assignment Methods

Static Translations

Dynamic Translations

Order of Operations

Inside-to-Outside Translation

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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
process is performed on the opposite addressing fields in the IP packet. When an outside
host sends a packet to the inside network, the NAT router translates the source
information (either the source address or the source address/port pair) and, in the
outbound direction, restores the original information (this time operating on the
destination address or address/port pair).
For inbound traffic, the NAT router translates the outside global address (or address/port)
into the outside local address (or address/port), either through a statically defined
translation or dynamically created translation. For outbound traffic, a translation must
be found to revert the outside local address (or address/port) into the outside global
address (or address/port), or the packet is not routed into the outside network.
NOTE: Dynamic outside source translations are established by inbound
traffic.
You use outside source translation along with inside source translation to configure twice
NAT.
NAT uses one of two methods to assign a translated IP address: static translation or
dynamic translation.
You enter static translations as direct configuration settings that remain in the translation
table until you remove them. You use static translations when you must initiate
connections from both the inside and outside interfaces, or when the translation is not
subject to change.
Dynamic translations use access list rules, to determine whether to apply NAT to incoming
traffic, and NAT address pools, from which a NAT translation can obtain IP addresses.
You use dynamic translation when you want the NAT router to initiate and manage
address translation and session flows between address realms on demand.
This section describes the order of operations for both inside-to-outside and
outside-to-inside translation.
Inside-to-outside translation occurs in the following order:
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