IPv6 Mobility David Bush

Correspondent Node Operation DEF: Correspondent node is any node that is trying to communicate with a mobile node. This node can be either station or mobile itself.

Receiving Packets When receiving a packet from a mobile node, the Home Address option will be used. The correspondent node must then copy the Home Address into the IPv6 header. This processing must be done only after any other options are processed.

Validating any Binding Update Request Before dealing with any Binding Update, the request must be validated. In order to be considered valid, the packet must fulfill the following: The packet has to have valid AH or ESP header that will provide user authentication. The packet has to have valid AH or ESP header that will provide user authentication. The Home Address option must be valid. The Home Address option must be valid. The Sequence number must be greater that any previous requests. The Sequence number must be greater that any previous requests. Any request not satisfying these requirements is silently dropped.

Request to Cache a Binding When a correspondent node receives this request, it is to enter the update into it’s Binding Cache (or update if the entry is already there) In addition, a Lifetime period is specified and the Binding Update must be deleted after this time period.

Request to Delete a Binding When a request for deletion is received, the correspondent node must delete the Binding Update associated with the mobile node from it’s Binding Cache.

Sending Binding Acknowledgements A packet with any Binding Update request may include a request for an acknowledgement. If this is the case, the correspondent node should send an acknowledgement to the mobile node. A value in the status field of less than 128 means acceptance, and more than 128 means rejection.

Sending Binding Request Since there is a Lifetime period, the Binding Update must be deleted after this time period. However, if the correspondent node knows the Binding Cache entry is still active, it can send a request to the mobile node to update the Binding entry. This can even be done is any packet that is part of normal communication.

Cache Replacement Policy When the Binding Cache of a correspondent node becomes full, the node may choose to delete any entry except for a “home registration” entry. If a new request cannot be fulfilled because of lack of storage, the node will return a Binding Acknowledgement with status field set to value 131.

Sending Packet to a Mobile Node Before any packets are sent, the Binding Cache is searched for a matching entry. If there is an entry, the node will use a Routing header to send the packet to the mobile node’s care-of-address that is in the entry. If there is no entry, the packet will be send as usual.

Home Agent Operation DEF: A Home Agent is a router that is on the mobile node’s home link which the mobile node has registered with.

Receiving Router Advertisement Messages Home agents periodically send out multicast advertisements with the Home Agent bit set. This allows Home Agents to maintain a list of other Home Agents that it is connected to. If the Home Agent is not already in the list, it is added and the lifetime set. If it is in the list, the lifetime is reset.

Primary Care-of-Address Registration If a node receives a request to become a mobile node’s home agent and the node does not implement home agent functionality or is not servicing the mobile node’s subnet, it must reject the request. Otherwise, the home agent accepts the care-of-address registration and becomes the node’s Home Agent.

Primary Care-of-Address Registration Cont. The Home Agent then enters the care-of- address into it’s Binding Cache and marks it as a “home registration.” The Prefix Length is also saved. If the Acknowledge bit is set, an acknowledgement is sent to the node. Lastly, the Home Agent starts to intercept packets for the mobile node.

Primary Care-of-Address Deregistration If the node doesn’t have an entry in it’s Binding Cache for the mobile node that is a “home registration” the request is rejected. Otherwise, the entry is deleted, an acknowledgement sent and the node stops intercepting packets for that mobile node.

Intercepting Packets for a Mobile Node When a Home Agent receives a packet destined for a mobile node that has registered with it, the node must tunnel the packet to the mobile node using IPv6 encapsulation.

Tunneling Intercepted Packets to a Mobile Node An intercepted packet cannot be just forwarded to the mobile node using a Routing header. Instead the packet is tunneled to the mobile node using the Home Agents IP address as the source address and the care-of-address as the destination address.

Tunneling Intercepted Packets to a Mobile Node Cont. The mobile node receives the packet and processes it resulting in its decapsulation and processing of the original packet. Any packets addressed to the mobile node’s link-local address are not tunneled to the mobile node. Instead, an ICMP Destination Unreachable message is returned to the sender.

Mobile Node Operation DEF: A Mobile Node is any device implementing IP that can change it’s location while still communicating.

Sending Packets While Away from Home While away from home, the mobile node will be using it’s home address plus any number of care-of-addresses. If the care-of-address is used, no special processing is needed. If the home address is used and the mobile node is not at home, special processing must be used.

Sending Packets While Away from Home Cont. Mobile IP is invisible to higher layers so the original packet is formed with the home address as the source address. First the Home Address option is set and the Home Address is copied into the Home Address field. Then the Source Address is changed to on of the node’s care-of-address.

Forming New Care-of-Addresses A Mobile Node obtains a new care-of- address when it moves to a new link. It may also get one whenever it wants, but it may not do so more than once per second.

Sending Binding Updates to the Home Agent If a Mobile Node changes it’s primary care-of-address, it must register the new address with it’s Home Agent. To do so, it sends a Binding Update to the Home Agent with the Home Registration bit set, the Acknowledgement bit set and the care-of-address as the source address.

Sending Binding Updates to Correspondent Nodes A Mobile Node may choose to send a Binding Update to a Correspondent Node so that it’s current care-of-address will be cached. The Mobile Node then must put the IP address of the node, it’s Home Address and the remaining lifetime in it’s Binding Update List.

Retransmitting Binding Updates If a Mobile node sends a Binding Update with the Acknowledge bit set and does not receive an acknowledgement within one second, it should retransmit the update with the same sequence number. An exponential back-off process is used for all sequential failures. The max time however is 256 seconds.

Rate Limiting for Sending Binding Updates A Mobile Node may send Binding Updates once per second at most. If 5 consecutive Binding Updates are sent and fail, the node must reduce its rate to sending only once every 10 seconds. It may continue at this rate indefinitely.

Receiving Binding Acknowledgements If a Binding Acknowledgement that indicates success is received, the Mobile Node updates the appropriate entry in it’s Binding Update List and stops sending update requests. If the Acknowledgement indicates failure, the appropriate entry is removed from the list and the node stops sending updates.

Receiving Binding Requests A Mobile Node may receive a request for a Binding Update from a correspondent node. The Mobile Node can then send a Binding Update with a new lifetime to the node. Or the Mobile Node can send the Update with a lifetime of zero to deny the request.

Using Multiple Care-of-Addresses When a Mobile Node has several care-of- addresses, it will select one to be it’s primary care-of-address. To do so, the node sends a Binding Update to it’s Home Agent with the Home Registration and Acknowledge bits set. After changing the primary care-of- address, the node must still accept packet from that address.

Returning Home Once a Mobile Node returns to it’s home link, it will notify it’s Home Agent by sending it a Binding Update. The Update will have it’s home address as the care-of-address and the Home Registration and Acknowledge bits set. Also, the node must multicast onto the home link to advertise that is has returned.

Security Concern Even with the validation of Binding Updates, Home Registration, etc. there is still concern. Mobile Nodes are more suseptible to theft than non-mobile nodes and so additional security methods need to be used especially where encryption keys or authentication information are stored on the node itself.