Outside-To-Inside Translation; Pptp And Gre Tunneling Through Nat - Juniper JUNOSE SOFTWARE FOR E SERIES 11.3.X - IP SERVICES CONFIGURATION GUIDE 2010-10-01 Configuration Manual

Outside-to-Inside Translation

PPTP and GRE Tunneling Through NAT

Copyright © 2010, Juniper Networks, Inc.
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.
The server module performs the appropriate translation.
4.
The router forwards the packet to the appropriate egress line module.
5.
The line module sends the packet as outbound traffic using a globally unique source
6.
address (inside source translation), destination address (outside source translation),
and ports (NAPT).
Outside-to-inside translation occurs in the following order:
Traffic from the outside, public domain enters the router.
1.
All traffic from an interface that is marked outside, whether or not it requires NAT, is
2.
sent to the server module.
The server module searches for an associated NAT match.
3.
If the server module:
4.
Finds a NAT match, and the destination interface is marked as inside, the server
module performs the appropriate translation and sends the packet to the appropriate
destination.
Does not find a NAT match, and the destination interface is marked as inside, the
server module drops the packet.
Does not find a NAT match, and the destination interface is not marked as inside,
the server module processes the packet normally for its destination.
You can configure NAT traversal support for GRE flows using simple translations (Basic
NAT). Because PPTP uses an enhanced GRE encapsulation for the PPP payload,
configuring for GRE flows also supports NAT traversal for PPTP tunnels.
NOTE: Neither port translation (NAPT) nor Firewall traversal for GRE packets
is supported for GRE flows.
When configured, the following types of translations are supported for GRE and PPTP
tunnels:
Inside source static simple translations (inbound and outbound)
Outside source static simple translations (inbound and outbound)
Chapter 2: Configuring NAT
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