HP-UX Mobile IPv4 A.03.01 Administrator's Guide
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Chapter 1
4
Figure 1-1 shows the data flow from a Correspondent Node to a Mobile Node using a
Foreign Agent Care-of Address.
Figure 1-1 Data Path for Foreign Agent Care-of Address
Note that the data transmission between the Foreign Agent and the Mobile Node must
bypass the normal IP routing mechanism since the Mobile Node’s home address is not
topologically correct for the foreign network. The Foreign Agent and the Mobile Node
must be attached to the same network segment and must determine each other’s
link-level address. The HP-UX Mobile IPv4 Foreign Agent determines the Mobile Node’s
link-level address from the link-level packet header.
Figure 1-1 also shows a high-level representation of the IP packet structure and IP
addresses as packets travel from the Correspondent Node to the Mobile Node. The
Correspondent Node first transmits a packet with its IP address as the source address,
and the Mobile Node’s IP address as the destination address (a). This packet is captured
by the Home Agent, which encapsulates the original packet in a new IP packet, with the
Home Agent’s IP address as the source, and the Foreign Agent Care-of Address as the
destination (b). The Foreign Agent receives the packet, removes the outer header, and
sends the original packet to the Mobile Node (c).
Co-located Care-of Address
When a Mobile Node uses a Co-located Care-of Address, the Mobile Node gets an
address on the foreign network without using Mobile IPv4 (by using a mechanism such
as DHCP) and associates it with one of its own network interfaces. The Mobile Node
receives the encapsulated packets directly from its Home Agent and decapsulates them.
Figure 1-2 shows the data flow from a Correspondent Node to a Mobile Node using a
Co-located Care-of Address. The Correspondent Node first transmits a packet with its IP
address as the source address, and the Mobile Node’s IP address as the destination
address (a). This packet is captured by the Home Agent, which encapsulates the original
packet in a new IP packet, with the Home Agent’s IP address as the source, and the