Clients On An Outside Network; Gre Flows Through Nat; Figure 11: Pptp Tunnels On An Outside Network - 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

Clients on an Outside Network

GRE Flows Through NAT

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through NAT, all matching PPTP control packets are translated and forwarded to the
destination.
In this example, an outside subscriber initiates PPTP tunnels to a PPTP server located
in the service provider network. The PPTP connection to the server traverses an E Series
router that has NAT enabled.

Figure 11: PPTP Tunnels on an Outside Network

The router has installed an inside source static simple translation in its translation table
as follows:
Inside Local Address
11.11.11.1
The PPTP client initiates its tunnels to the inside global address 20.0.0.1. The E Series
router translates packets destined for address 20.0.0.1 and forwards them to the inside
local address of 11.11.11.1. Because GRE traffic can pass through NAT, all matching PPTP
control packets are translated and forwarded to the destination.
Because PPTP requires the use of GRE flows, the examples in the previous section also
work for any GRE traffic flows that traverse NAT.
GRE flows can terminate at an E Series router if NAT is or is not enabled. When the router
receives locally terminating inbound GRE packets, the router transmits the packets to
the tunnel server module for GRE processing. If the packets require translating, they are
again sent through the tunnel server module.
NOTE: Only inner IP headers are translated for terminating GRE flows; outer
IP headers are never translated.
For outbound GRE packets, the process works in reverse. If the packets require translation,
the router transmits the packets to the tunnel server module for translation. If the packets
are destined for a GRE tunnel, they are again sent through the tunnel server module where
an outer header is prepended to the packet and the packet is then sent to the appropriate
GRE tunnel.
Inside Global Address
20.0.0.1
Copyright © 2010, Juniper Networks, Inc.