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JunosE 11.2.x IP Services Configuration Guide
Address Assignment Methods
Static Translations
Dynamic Translations
Order of Operations
Inside-to-Outside Translation
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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:
Inside (privately addressed) traffic enters the router on an interface marked as inside.
1.
A route lookup is performed.
2.
If the next interface is marked as outside, the router sends the traffic to the server
3.
module.
Copyright © 2010, Juniper Networks, Inc.
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