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TCP/IP Tutorial and Technical Overview - IBM Redbooks

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<strong>IP</strong>v6/<strong>IP</strong>v4 Host<br />

Ethernet<br />

<strong>IP</strong>v6/<strong>IP</strong>v4 Router<br />

Figure 9-26 Router-to-host automatic tunneling<br />

Figure 9-27 on page 385 shows the host-to-host tunneling scenario. Here<br />

workstation B responds as follows:<br />

1. Workstation B has no <strong>IP</strong>v6-capable router on its local link. It therefore adds<br />

an <strong>IP</strong>v4 header to its own <strong>IP</strong>v6 frame <strong>and</strong> forwards the resulting <strong>IP</strong>v4<br />

datagram directly to the <strong>IP</strong>v4 address of workstation A through the <strong>IP</strong>v4<br />

network. This is host-to-host automatic tunneling.<br />

2. The <strong>IP</strong>v4 datagram is received by the <strong>IP</strong>v4 stack of workstation A. Because<br />

the Protocol field shows that the next header is 41 (<strong>IP</strong>v6), the <strong>IP</strong>v4 header is<br />

stripped from the datagram <strong>and</strong> the remaining <strong>IP</strong>v6 packet is then h<strong>and</strong>led by<br />

the <strong>IP</strong>v6 stack.<br />

384 <strong>TCP</strong>/<strong>IP</strong> <strong>Tutorial</strong> <strong>and</strong> <strong>Technical</strong> <strong>Overview</strong><br />

(1)<br />

A<br />

6 4 flow label<br />

payload length next hops<br />

src: Workstation A<br />

(<strong>IP</strong>v4-compatible)<br />

dst: Workstation B<br />

(<strong>IP</strong>v4-compatible)<br />

payload<br />

<strong>IP</strong>v4<br />

Header<br />

<strong>IP</strong>v4<br />

Network<br />

X Y<br />

(2)<br />

4<br />

nxt:41<br />

src: Workstation A (<strong>IP</strong>v4)<br />

dst: Workstation B (<strong>IP</strong>v4)<br />

6 4 flow label<br />

payload length next hops<br />

src: Workstation A<br />

(<strong>IP</strong>v4-compatible)<br />

dst: Workstation B<br />

(<strong>IP</strong>v4-compatible)<br />

payload<br />

<strong>IP</strong>v6/<strong>IP</strong>v4 Router<br />

4<br />

B<br />

<strong>IP</strong>v6/<strong>IP</strong>v4 Host<br />

(3)<br />

nxt:41<br />

src: Workstation A (<strong>IP</strong>v4)<br />

dst: Workstation B (<strong>IP</strong>v4)<br />

6 4 flow label<br />

payload length next hops<br />

src: Workstation A<br />

(<strong>IP</strong>v4-compatible)<br />

dst: Workstation B<br />

(<strong>IP</strong>v4-compatible)<br />

payload

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