Gre Overview; Introduction To Gre - 3Com MSR 50 Series Configuration Manual

81

GRE Overview

Introduction to GRE

GRE C
ONFIGURATION
When configuring GRE, go to these sections for information you are interested in:
"GRE Overview" on page 1589
■
"Configuring a GRE over IPv4 Tunnel" on page 1593
■
"Configuring a GRE over IPv6 Tunnel" on page 1594
■
"Displaying and Maintaining GRE" on page 1596
■
"GRE over IPv4 Tunnel Configuration Example" on page 1596
■
"GRE over IPv6 Tunnel Configuration Example" on page 1598
■
"Troubleshooting GRE" on page 1600
■
Generic routing encapsulation (GRE) is a protocol designed for performing
encapsulation of one network layer protocol (for example, IP or IPX) over another
network layer protocol (for example, IP). GRE uses the tunneling technology and
serves as a Layer 3 tunneling protocol of virtual private network (VPN).
A tunnel is a virtual point-to-point connection for transferring encapsulated
packets. Packets are encapsulated at one end of the tunnel and decapsulated at
the other end.
A packet transferred through a tunnel undergoes an encapsulation process and a
decapsulation process.
processes.
Figure 437 IPX networks interconnected through the GRE tunnel
Novell IPX protocol
Group 1
Encapsulation process
1 After receiving an IPX packet through the interface connected to IPX network
Group1, Router A submits it to the IPX module for processing.
2 The IPX module checks the destination address field in the IPX header to
determine how to route the packet.
3 If the packet must be tunneled to reach its destination, Router A sends it to the
tunnel interface.
Figure 437 depicts the network used to illustrate these two
Internet
GRE tunnel
Router A
Novell IPX protocol
Group 2
Router B