Mobile Internet basics: Mobile IPv6 technology overview
Route Optimization Mode
Route optimization mode in Mobile IPv6 allows the IPv6 network to use standard short-est-path (or policy-based) algorithms to determine how packets are routed from the correspondent node to the mobile node. This mode requires the correspondent node to support the Mobile IPv6 protocol.
Figure 5-28 below illustrates route optimization mode in Mobile IPv6. To populate the bindings database on the correspondent node, the mobile node sends Binding Update messages, similar to those sent to the home agent. The correspondent node maintains a bindings database that maps the mobile node’s home address and CoA.
Click on image to enlarge.
Figure 5-28. Mobile IPv6 route optimization mode
Packets from the mobile node toward the correspondent node are sent directly to the correspondent node. Packets from the correspondent node are routed directly to the CoA of the mobile node.
IPv6 Destination Option Header
In Mobile IPv6 route optimization mode, the mobile node sources all packets from its CoA. This is required to conform with reverse path forwarding (RPF), a technique for preventing IP address spoofing.
TCP sessions, as discussed in the introduction to this chapter, are bound to both source and destination IP addresses. Under normal circumstances, the TCP layer would break when the mobile node’s source IP address (CoA) changed, because the correspondent node’s TCP stack would no longer have an associated flow.
The Mobile IPv6 Destination Options header resolves this problem. In Mobile IPv6, the Destination Options header is used in packets sent by the mobile node to notify the correspondent node of its home address. The inclusion of the home address in this Destination Options header makes the use of the CoA for transport transparent above the network layer.
Figure 5-29 Mobile IPv6 Destination Options Header
The correspondent node replaces the IPv6 source address in the IPv6 header with the home address provided in the Destination Options header.
The replacing of the address with that recovered from the Options header ensures that the operation of route optimization is masked from the upper layer applications. Figure 5-29 above illustrates how a correspondent node uses the home address provided in the Destination Options header.
IPv6 Type 2 Routing Header
In Mobile IPv6 route optimization mode, the correspondent node uses the mobile node CoA as the destination for all packets. By ensuring that all packets are sent to the mobile node’s CoA, ingress filtering devices or devices that require topologically accurate source/destination address pairs continue to operate normally.
Under normal circumstances, the TCP layer would break when the mobile node changes point of attachment because the mobile node’s TCP stack would no longer have an associated flow. The Mobile IPv6 Type 2 Routing header resolves this problem.
In Mobile IPv6, the Type 2 Routing header is used in packets sent by the correspondent node to the mobile node. The correspondent node puts the mobile node’s home address in this header.
Figure 5-30. IPv6 mobility header structure
The mobile node replaces the IPv6 destination address in the IPv6 header with the home address provided in the Type 2 Routing header. Figure 5-30 above illustrates how a mobile node uses the home address provided in the Type 2 Routing header.
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