R0106-HP MSR Router Series Layer 3 - IP Services Configuration Guide(V7)

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{ Address Family Transition Router (AFTR)
An AFTR resides in the ISP network and terminates the tunnel from the B4 router. NAT is also
implemented on the interface that connects the public IPv4 network.
AFTR de-encapsulates the tunneled packet, translates the network address, and routes the
packet to the destination IPv4 network. For IPv4 packets coming from the public IPv4 network,
AFTR performs reverse address translation and sends them to the B4 router by using the DS-Lite
tunnel.
Figure 109 Packet forwarding process in DS-Lite
Figure 109 shows a packet passing through a DS-Lite tunnel between IPv4 networks.
a. Upon receiving a packet from the private IPv4 network, the B4 router adds an IPv6 header to
the packet and sends the IPv6 packet to the AFTR through the tunnel.
b. The AFTR does the following:
− Removes the IPv6 header of the tunneled packet.
− Assigns a tunnel ID for the B4 router.
− Records the mapping between the IPv6 address of the B4 router (the source IPv6 address of
the packet), and the tunnel ID.
c. After de-encapsulation, the AFTR translates the source private IPv4 address of the packet into
a public IPv4 address and sends the packet to the destination IPv4 host. The AFTR also maps
the NAT entries to the tunnel ID so that IPv4 networks connected to different B4 routers can use
the same address space.
d. Upon receiving the response packet from the public network, the AFTR translates the
destination public IPv4 address into the private IPv4 address. The AFTR does the following:
Private
IPv4 network
IPv4 network
IPv4 host
IPv4 host
B4
AFTR
IPv4 dst: 30.1.1.1
IPv4 src: 10.0.0.1
TCP dst: 80
TCP src: 10000
IPv4 dst: 20.1.1.1
IPv4 src: 30.1.1.1
TCP dst: 5000
TCP src: 80
IPv6 network
DS-Lite tunnel
30.1.1.1/2410.0.0.1/24
10.0.0.2/24 1::1/64 2::1/64 20.1.1.1/24
IPv6 dst: 2::1
IPv6 src: 1::1
IPv4 dst: 30.1.1.1
IPv4 src: 10.0.0.1
TCP dst: 80
TCP src: 10000
IPv4 dst: 30.1.1.1
IPv4 src: 20.1.1.1
TCP dst: 80
TCP src: 5000
IPv6 dst: 1::1
IPv6 src: 2::1
IPv4 dst: 10.0.0.1
IPv4 src: 30.1.1.1
TCP dst: 10000
TCP src: 80
IPv4 dst: 10.0.0.1
IPv4 src: 30.1.1.1
TCP dst: 10000
TCP src: 80
Removes the
IPv6 header
and performs
NAT
Performs NAT
and adds an
IPv6 header
Removes
the IPv6
header
Adds an IPv6
header