44
C
ONFIGURING
GRE
This chapter covers the following topics:
■
GRE Protocol Overview
■
Configuring GRE
■
Displaying and Debugging GRE
■
GRE Configuration Example
■
Troubleshooting GRE
GRE Protocol
Overview
The Generic Routing Encapsulation (GRE) protocol encapsulates datagram of
network layer protocols, such as IP and IPX, and enables these encapsulated
datagrams to transmit in another network layer protocol, such as IP. GRE is a Layer
3 protocol that creates Virtual Private Network (VPN) tunnels. A tunnel is a virtual
point-to-point connection and is a virtual interface that only supports
point-to-point connections. It is necessary to encapsulate and de-encapsulate it
when a message is transmitted on the tunnel. The interface provides a channel
where the encapsulated datagram can be transmitted. The interface also
encapsulates and de-encapsulates the datagram at both ends of a tunnel.
Encapsulation
As shown in Figure 198, after receiving an IPX datagram, the interface connecting
“Group1” first delivers it to be processed by the IPX protocol which checks the
destination address domain in the IPX header and determines how to route the
packet.
Figure 198
Typical networking diagram of GRE
If it is found that the destination address of the message will route through the
network with network number 1f (virtual network number of the tunnel), the
message will be transmitted to the tunnel port with network number 1f. After
receiving the packet, the tunnel port will perform GRE and then, the packet will be
processed by the IP module. After IP header is encapsulated, the packet will be
processed by the corresponding network interface according to the destination
address and router table.
De-encapsulation
The de-encapsulation is the opposite of encapsulation. When an IP message is
received at a tunnel interface, its destination address is checked and if the router is
the destination, then the IP header is removed and processed by the GRE protocol,
IPX protocol
Group1
Internet
IPX protocol
Group2
Tunnel
Router A
Router B
Summary of Contents for 3036
Page 1: ...http www 3com com 3Com Router Configuration Guide Published March 2004 Part No 10014299 ...
Page 4: ...VPN 615 RELIABILITY 665 QOS 681 DIAL UP 721 ...
Page 6: ...2 ABOUT THIS GUIDE ...
Page 7: ...I GETTING STARTED Chapter 1 3Com Router Introduction Chapter 2 3Com Router User Interface ...
Page 8: ...4 ...
Page 16: ...12 CHAPTER 1 3COM ROUTER INTRODUCTION ...
Page 34: ...30 ...
Page 60: ...56 CHAPTER 3 SYSTEM MANAGEMENT ...
Page 98: ...94 CHAPTER 6 DISPLAY AND DEBUGGING TOOLS ...
Page 110: ...106 ...
Page 114: ...110 CHAPTER 8 INTERFACE CONFIGURATION OVERVIEW ...
Page 158: ...154 CHAPTER 10 CONFIGURING WAN INTERFACE ...
Page 168: ...164 ...
Page 188: ...184 CHAPTER 13 CONFIGURING PPPOE CLIENT ...
Page 192: ...188 CHAPTER 14 CONFIGURING SLIP Router ip route static 0 0 0 0 0 0 0 0 10 110 0 1 ...
Page 248: ...244 CHAPTER 16 CONFIGURING LAPB AND X 25 ...
Page 320: ...316 ...
Page 330: ...326 CHAPTER 20 CONFIGURING IP ADDRESS ...
Page 362: ...358 CHAPTER 21 CONFIGURING IP APPLICATION ...
Page 374: ...370 CHAPTER 23 CONFIGURING IP COUNT ...
Page 406: ...402 CHAPTER 25 CONFIGURING DLSW ...
Page 408: ...404 ...
Page 452: ...448 CHAPTER 29 CONFIGURING OSPF ...
Page 482: ...478 CHAPTER 30 CONFIGURING BGP ...
Page 494: ...490 CHAPTER 31 CONFIGURING IP ROUTING POLICY ...
Page 502: ...498 ...
Page 508: ...504 CHAPTER 33 IP MULTICAST ...
Page 514: ...510 CHAPTER 34 CONFIGURING IGMP ...
Page 526: ...522 CHAPTER 36 CONFIGURING PIM SM ...
Page 528: ...524 ...
Page 532: ...528 CHAPTER 37 CONFIGURING TERMINAL ACCESS SECURITY ...
Page 550: ...546 CHAPTER 38 CONFIGURING AAA AND RADIUS PROTOCOL ...
Page 590: ...586 CHAPTER 40 CONFIGURING IPSEC ...
Page 599: ...IX VPN Chapter 42 Configuring VPN Chapter 43 Configuring L2TP Chapter 44 Configuring GRE ...
Page 600: ...596 ...
Page 638: ...634 CHAPTER 43 CONFIGURING L2TP ...
Page 649: ...X RELIABILITY Chapter 45 Configuring a Standby Center Chapter 46 Configuring VRRP ...
Page 650: ...646 ...
Page 666: ...662 ...
Page 670: ...666 CHAPTER 47 QOS OVERVIEW ...
Page 700: ...696 CHAPTER 49 CONGESTION MANAGEMENT ...
Page 706: ...702 CHAPTER 50 CONGESTION AVOIDANCE ...
Page 707: ...XII DIAL UP Chapter 51 Configuring DCC Chapter 52 Configuring Modem ...
Page 708: ...704 ...
Page 762: ...758 CHAPTER 52 CONFIGURING MODEM ...