3Com 10014299 manual Encapsulated tunnel message format Refer to RFC

636CHAPTER 44: CONFIGURING GRE

which examines the key, checksum or message sequence number. After the GRE header is removed, the IP message is processed by the IPX protocol in the same way as an ordinary datagram.

The system receives a datagram to be encapsulated and routed,. The datagram is first encapsulated in the GRE message so that the datagram is the payload of a GRE message. Then the datagram is encapsulated in an IP message. The IP layer forwards the message. The IP protocol that forwards the messages is often called a delivery protocol or transport protocol.

The form of an encapsulated message is shown in Figure 199:

Figure 199 Encapsulated tunnel message format (Refer to RFC)

Delivery Header

(Transport Protocol)

GRE Header

(Encapsulation Protocol)

Payload Packet

(Passenger Protocol)

For example: The format of IPX transmission message that is encapsulated in an IP tunnel is as follows:

Figure 200 Format of transmission message in the tunnel.

IP GRE IPX

Passenger Protocol

Carrier Protocol or

Encapsulation Protocol

Transport Protocol