HP 6125XLG R2306-HP 6125XLG Blade Switch Layer 3 - IP Services Configuration G - Page 193

GRE encapsulation and de-encapsulation, Encapsulation process, Protocols and standards

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GRE encapsulation and de-encapsulation Figure 81 X protocol networks interconnected through a GRE tunnel The following takes the network shown in Figure 81 as an example to describe how an X protocol packet traverses an IP network through a GRE tunnel: Encapsulation process 1. After receiving an X protocol packet from the interface connected to Group 1, Device A submits it to the X protocol for processing. 2. The X protocol checks the destination address field in the packet header to determine how to route the packet. 3. If the packet must be tunneled to reach its destination, Device A sends it to the GRE tunnel interface. 4. Upon receiving the packet, the tunnel interface encapsulates the packet with GRE and then with IP. 5. Device A looks up the routing table according to the destination address in the IP header and forwards the IP packet. De-encapsulation process De-encapsulation is the reverse of the encapsulation process: 1. Upon receiving an IP packet from the tunnel interface, Device B checks the destination address. 2. If the destination is itself and the protocol number in the IP header is 47 (the protocol number for GRE), Device B removes the IP header of the packet and submits the resulting packet to GRE for processing. 3. After GRE finishes the processing, Device B removes the GRE header and submits the payload to the X protocol for forwarding. NOTE: GRE encapsulation and de-encapsulation can decrease the forwarding efficiency of tunnel-end devices. Protocols and standards • RFC 1701, Generic Routing Encapsulation (GRE) • RFC 1702, Generic Routing Encapsulation over IPv4 networks • RFC 2784, Generic Routing Encapsulation (GRE) Configuring a GRE over IPv4 tunnel Follow these guidelines when you configure a GRE over IPv4 tunnel: 185

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185
GRE encapsulation and de-encapsulation
Figure 81
X protocol networks interconnected through a GRE tunnel
The following takes the network shown in
Figure 81
as an example to describe how an X protocol packet
traverses an IP network through a GRE tunnel:
Encapsulation process
1.
After receiving an X protocol packet from the interface connected to Group 1, Device A submits it
to the X protocol for processing.
2.
The X protocol checks the destination address field in the packet header to determine how to route
the packet.
3.
If the packet must be tunneled to reach its destination, Device A sends it to the GRE tunnel interface.
4.
Upon receiving the packet, the tunnel interface encapsulates the packet with GRE and then with IP.
5.
Device A looks up the routing table according to the destination address in the IP header and
forwards the IP packet.
De-encapsulation process
De-encapsulation is the reverse of the encapsulation process:
1.
Upon receiving an IP packet from the tunnel interface, Device B checks the destination address.
2.
If the destination is itself and the protocol number in the IP header is 47 (the protocol number for
GRE), Device B removes the IP header of the packet and submits the resulting packet to GRE for
processing.
3.
After GRE finishes the processing, Device B removes the GRE header and submits the payload to
the X protocol for forwarding.
NOTE:
GRE encapsulation and de-encapsulation can decrease the forwarding efficiency of tunnel-end devices.
Protocols and standards
•
RFC 1701, Generic Routing Encapsulation (GRE)
•
RFC 1702, Generic Routing Encapsulation over IPv4 networks
•
RFC 2784, Generic Routing Encapsulation (GRE)
Configuring a GRE over IPv4 tunnel
Follow these guidelines when you configure a GRE over IPv4 tunnel: