R3721-F3210-F3171-HP High-End Firewalls VPN Configuration Guide-6PW101

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• De-encapsulation
The de-encapsulation follows these steps:
a. After receiving the packet, Device A delivers it to the IP protocol stack, which then checks the
protocol number in the IP header.
b. If the protocol number is IPv4 (indicating an IPv4 packet is encapsulated within the packet), the
IP packet is sent to the tunnel module for de-encapsulation.
c. The de-encapsulated IP packet is sent back to the IP protocol stack for processing.
IPv4 over IPv6 tunneling
Introduction
IPv4 over IPv6 tunneling adds an IPv6 header to IPv4 packets so that the IPv4 packets can traverse an
IPv6 network and reach another IPv4 network.
Encapsulation and de-encapsulation
Figure 68 Principle of IPv4 over IPv6 tunneling
The encapsulation and de-encapsulation processes illustrated in Figure 71 are described as follows:
• Encapsulation
a. Upon receiving a packet from the attached IPv4 network, Device A examines the destination
address of the packet and determines the outgoing interface.
b. If the packet is destined for the IPv4 network attached to Device B, Device A delivers the packet
to the tunnel interface pointed to Device B.
c. The tunnel interface adds an IPv6 header to the original IPv4 packet and delivers the packet to
the IPv6 protocol stack for forwarding.
• De-encapsulation
a. Upon receiving a packet from the attached IPv6 network, Device B delivers the packet to the
IPv6 protocol stack to examine the protocol type encapsulated in the data portion of the
packet.
b. If the protocol type is IPv4, the IPv6 protocol stack delivers the packet to the tunneling module.
c. The tunneling module removes the IPv6 header and delivers the remaining IPv4 packet to the
IPv4 protocol stack for subsequent forwarding.
IPv4 over IPv6 tunnel modes
IPv4 over IPv6 tunnels fall into the following modes: