R2511-HP MSR Router Series Layer 3 - IP Services Configuration Guide(V5)

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The encapsulation and de-encapsulation processes illustrated in Figure 79 are described as follows:
• Encapsulation:
a. Upon receiving a IPv4 packet, Device A delivers it to the IPv4 protocol stack.
b. The IPv4 protocol stack uses the destination address of the packet to determine the output
interface. If the output interface is the tunnel interface, the IPv4 protocol stack delivers the
packet to the tunnel interface.
c. The tunnel interface adds an IPv6 header to the original IPv4 packet and delivers the packet to
the IPv6 protocol stack.
d. The IPv6 protocol stack uses the destination IPv6 address of the packet to look up the routing
table and sends it out.
• De-encapsulation:
e. Upon receiving the IPv6 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.
f. If the protocol type is IPv4, the IPv6 protocol stack delivers the packet to the tunneling module.
g. The tunneling module removes the IPv6 header and delivers the remaining IPv4 packet to the
IPv4 protocol stack.
h. The IPv4 protocol stack forwards the IPv4 packet.
IPv4 over IPv6 tunnel modes
IPv4 over IPv6 tunnels include the following modes:
• IPv4 over IPv6 manual tunnel
In this tunnel mode, you must manually configure the source and destination IPv6 addresses for the
tunnel. An IPv4 over IPv6 manual tunnel is a point-to-point virtual link.
• DS-Lite tunnel
Dual Stack Lite (DS-Lite) combines the IPv4 over IPv6 tunneling and network address translation
(NAT) to connect IPv4 networks over IPv6 networks without sacrificing the benefits of NAT.
Figure 80 DS-Lite network diagram
As shown in Figure 80, a DS-Lite network involves the following parts:
Private
IPv4 network
DS-lite tunnel
IPv4 network
IPv4 host IPv4 host
CPE
AFTR
IPv6 network
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DS-lite host
Subscriber network ISP core network Internet