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C
HAPTER
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ONFIGURING
L2TP
The L2TP header includes the information of tunnel and session IDs, which are
used to identify different tunnels and sessions. The messages with the same tunnel
ID and different session IDs is multiplexed in one tunnel. Tunnel ID and session ID
are distributed to the opposite end of the tunnel.
L2TP detects the connectivity of a tunnel using a Hello message. When the tunnel
is idle for some time, LAC and LNS begin to transmit the Hello message to the
opposite end. If no response to the Hello message is received for some time, the
sessionis cleared up.
Control message and data message
L2TP has two types of messages: control message and data message. The control
message is used to establish, maintain and transmit the tunnel and session
connection. The data message is used to encapsulate the PPP frame and transmit
it in the tunnel. The transmission of a control message is reliable, but data
message transmission is not reliable. If a data message is lost, it is not transmitted
again. L2TP supports flow control and congestion control only for control
messages, not for data messages.
L2TP is transmitted in the form of a UDP message. L2TP registers UDP Port 1701,
which is used only for initial tunnel establishment. Originating side of L2TP tunnel
randomly selects an idle port (it need not to be 1701) and transmits a message to
1701 port of receiving side. After receiving the message, the receiving side
randomly selects an idle port (it need not to be 1701 and transmits a message
back to the specified port of the originating side. By now, the selected ports of
both sides are selected and remain unchanged during the time segment when the
tunnel is connected.
After being transmitted to L2TP and encapsulated with L2TP header, the PPP
frame will be eventually encapsulated into UDP messages and transmitted on a
TCP/IP network.
IV. Call setup flow of L2TP tunnel
Call setup flow of L2TP tunnel is shown in the following figure:
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 ...