H3C Technologies H3C SecPath F1000-E - Manual (Page 152)

6
IPv4 over IPv4 Tunnel
Introduction to IPv4 over IPv4 tunneling protocol
The IPv4 over IPv4 tunneling protocol (RFC 1853) is developed for IP data packet encapsulation so that
data can be transferred from one IPv4 network to another IPv4 network.
Encapsulation and de-encapsulation
Packets traveling through a tunnel undergo an encapsulation and de-encapsulation process. Figure 4
shows these two processes.
Figure 4 Principle of IPv4 over IPv4 tunnel
• Encapsulation
The encapsulation process is as follows:
1. The interface of Router A connecting to an IPv4 host receives an IP packet and submits it to the IP
protocol stack for processing.
2. The IP protocol stack determines how to route the packet according to the destination address in
the IP header. If the packet needs to be routed to the IPv4 host connected to Router B, the packet
is sent to Router A’s tunnel interface that is connected to Router B.
3. After the tunnel interface receives the packet, the packet is added with an outer IPv4 header and
submitted to the IP protocol stack for processing. The IP protocol stack determines the outgoing
interface of the tunnel according to the IP header.
• De-encapsulation
Contrary to the encapsulation process, the de-encapsulation process is as follows:
1. The IP packet received from the IPv4 network interface is sent to the IP protocol stack, which then
checks the protocol number in the IP header.
2. If the protocol number is IPv4, the IP packet is sent to the tunnel module for de-encapsulation.
3. The de-encapsulated IP packet is sent back to the IP protocol stack for processing.
IPv4/IPv6 over IPv6 Tunnel
Introduction to IPv4/IPv6 over IPv6 tunneling protocol
The IPv4/IPv6 over IPv6 tunneling protocol (RFC 2473) is developed for IPv4 or IPv6 data packet
encapsulation so that encapsulated packets can be transmitted over an IPv6 network. The encapsulated
packets are IPv6 tunnel packets.