Mobile IPv6 Message Exchanges

472 Understanding IPv6, Second Edition

Note In Figure F-14 and subsequent figures, CNA is the correspondent node’s address, CoA is the mobile node’s care-of address, HoA is the mobile node’s home address, and HAA is the home agent’s global address.

Correspondent

Node

Figure F-14 Data packets sent by a correspondent node to the mobile node’s home address

These packets contain the following:

■IPv6 header In the IPv6 header, the source address is the correspondent node address and the destination address is the mobile node’s home address. Because a binding cache entry does not exist, the correspondent node sends the packet as if the mobile node were physically attached to the home link.

■Upper layer PDU The upper-layer PDU contains the Application layer data sent from the correspondent node to the mobile node.

When the home agent intercepts a packet sent to a mobile node’s home address, it tunnels the packet to the mobile node using the form shown in Figure F-15.

Figure F-15 Intercepted packet tunneled to a mobile node by its home agent

These packets contain the following:

■IPv6 header (outer) In the outer IPv6 header, the source address is the home agent’s address on the home link and the destination address is the mobile node’s care-of address.

■IPv6 header (inner) In the inner IPv6 header, the source address is the correspondent node’s address and the destination address is the mobile node’s home address.

■Upper-layer PDU The upper-layer protocol data unit (PDU) contains the Application layer data sent from the correspondent node to the mobile node at its home address. From the Application layer perspective, the data was addressed from the correspondent node address to the home address.

Optionally, the home agent can protect the packet by using IPsec ESP. In this case, an ESP header is placed between the outer IPv6 header and the inner IPv6 header (not shown

in Figure F-15).

When the correspondent registration process is not yet complete or the correspondent node is not Mobile IPv6–capable, the mobile node that is away from home sends packets to the correspondent node by tunneling them to the home agent, as shown in Figure F-16.

■IPv6 header (outer) In the outer IPv6 header, the source address is the mobile node’s care-of address and the destination address is the home agent’s address on the home link.

■IPv6 header (inner) In the inner IPv6 header, the source address is the mobile node’s home address and the destination address is the correspondent node’s address.

■Upper-layer PDU The upper-layer PDU contains the Application layer data sent from the mobile node to the correspondent node.

Optionally, the mobile node can protect the packet by using IPsec ESP. In this case, an ESP header is placed between the outer IPv6 header and the inner IPv6 header (not shown

in Figure F-16).

The home agent forwards tunneled data packets from a mobile node that is away from home to a correspondent node using the form shown in Figure F-17.

476Understanding IPv6, Second Edition

■For short-term communication that does not require a logical connection, such as the exchange of Domain Name System (DNS) Name Query Request and Name Query Response messages for DNS name resolution, the mobile node can send data from its care-of address and not use a Home Address option. In this case, the mobile node is sending and receiving packets normally from its care-of address.

Figure F-18 shows data packets sent directly from the mobile node to the correspondent node when the mobile node has a binding update list entry for the correspondent node’s address.

Figure F-18 Data sent from the mobile node to the correspondent node

These packets contain the following:

■IPv6 header In the IPv6 header, the source address is the mobile node’s care-of address and the destination address is the correspondent node’s address. By using the care-of address rather than the home address, ingress filtering by the foreign-link router does not prevent the packet from being forwarded.

■Destination Options header In the Destination Options extension header, the Home Address option contains the home address of the mobile node. When the correspondent node processes the Home Address option, it replaces the source address of the packet with the home address.

■Upper-layer PDU The upper-layer (PDU contains the Application layer data sent from the mobile node to the correspondent node. From the Application layer perspective, the data was addressed from the home address to the correspondent node address.

Note The drawings in this appendix assume that the data packets being sent by the mobile node and the correspondent node do not contain additional IPv6 extension headers.

If the correspondent node is also a mobile node that is away from home, the destination address in the IPv6 header is set to the correspondent node’s care-of address and the packet includes a Type 2 Routing header with the correspondent node’s home address. The Type 2 Routing header is placed before the Destination Options header. This is not shown in Figure F-18.

Figure F-19 shows the form of data packets sent from the correspondent node to the mobile node when the correspondent node has a binding cache entry for the mobile node’s home address.

Figure F-19 Data sent from the correspondent node when a binding cache entry for the mobile node is present