Survey on network mobility support <s> V. NEMO Basic Support <s> This document specifies Mobile IPv6, a protocol which allows nodes to ::: remain reachable while moving around in the IPv6 Internet. Each mobile ::: node is always identified by its home address, regardless of its ::: current point of attachment to the Internet. While situated away from ::: its home, a mobile node is also associated with a care-of address, ::: which provides information about the mobile node's current ::: location. IPv6 packets addressed to a mobile node's home address ::: are transparently routed to its care-of address. The protocol enables ::: IPv6 nodes to cache the binding of a mobile node's home address ::: with its care-of address, and to then send any packets destined for ::: the mobile node directly to it at this care-of address. To support ::: this operation, Mobile IPv6 defines a new IPv6 protocol and a new ::: destination option. All IPv6 nodes, whether mobile or stationary, can ::: communicate with mobile nodes. This document obsoletes RFC 3775. <s> BIB001 </s> Survey on network mobility support <s> V. NEMO Basic Support <s> This document specifies protocol enhancements that allow transparent routing of IP datagrams to mobile nodes in the Internet. Each mobile node is always identified by its home address, regardless of its current point of attachment to the Internet. While situated away from its home, a mobile node is also associated with a care-of address, which provides information about its current point of attachment to the Internet. The protocol provides for registering the care-of address with a home agent. The home agent sends datagrams destined for the mobile node through a tunnel to the care- of address. After arriving at the end of the tunnel, each datagram is then delivered to the mobile node. <s> BIB002
The objective of the IETF NEMO working group is to develop mechanisms that provide permanent Internet connectivity to all mobile network nodes via their permanent IP addresses as well as maintain ongoing sessions as the mobile network changes its point of attachment to the Internet. Existing protocols such as MIP and MIPv6 that provide host mobility support are not sufficient due to two reasons. Firstly, not all devices in a mobile network such as the sensors on an aircraft may be sophisticated enough to run these complex protocols. Secondly, once a device has attached to the MR on a mobile network, it may not see any link-level handoffs even as the network moves. Thus the host mobility protocols such as MIP and MIPv6 do not get triggers indicating link-level handoffs and as a result will not initiate handover. In the network mobility architecture the MR takes care of all the nodes within the network irrespective of their capabilities. As a first step, the IETF NEMO Working Group is developing a basic protocol  that ensures uninterrupted connectivity to the mobile network nodes, without considering issues such as route optimization. This protocol runs on the MR and its Home Agent (HA) and uses the same mechanisms as the host mobility protocols. The NEMO Basic protocol requires the MR to act on behalf of the nodes within its mobile network. Firstly, the MR indicates to it's HA that it is acting as a MR as opposed to a mobile host. Secondly, the MR informs the HA of the mobile network prefixes. These prefixes are then used by the HA to intercept packets addressed to the mobile nodes and tunnel them to the MR (at its care-of address), which in turn decapsulates the packets and forwards them to the mobile nodes. Packets in the reverse direction are also tunneled via the HA in order to overcome Ingress filtering restrictions  . In this case the HA decapsulates the packets and forwards them to the Correspondent Nodes. This tunneling of packets is very much in the spirit of MIP and MIPv6. Note however, that NEMO differs from MIP/MIPv6 in that the MR updates the HA with the location of the entire mobile network, not just itself. One way for the MR to update the HA is to augment the Binding Update message to include the mobile network prefix along with the MR's care-of address. This use of a Prefix Scope Binding Update (PSBU), proposed by Ernst  , allows a single care-of address to be associated with a prefix rather than a single home address. Furthermore only a single PSBU message is required for the entire network, preserving route aggregation. Another proposal by Kniveton et al  uses a routing protocol between the MR and it's HA. In this case the MR need not include prefix information in the Binding Update. Petrescu et al  suggest the use of ICMP redirect messages to inform the HA of routes towards the MR. Alternatively, static routes could be configured to the Mobile Network via the MR's Home Address. This approach has the benefit that it does not incur additional signaling overheads. The main drawback of having static configuration is that it would prevent deployment. Another negative effect of statically configuring routes to the Mobile Network Prefixes is that these routes are present even if the related MR is unreachable. The NEMO basic support protocol adopts a flexible approach by leaving the implementers of the protocol to adopt any of the above methods when informing the HA of the routes towards the MR. To illustrate how connectivity to mobile network nodes is achieved with the NEMO basic protocol, consider again the aircraft scenario depicted in Figure 1 , with the aircraft at a foreign airport. Assume that a centralized database server needs to update the information panels in the compartments with the current times and the weather conditions of stopover cities en-route back to the home city. Assume that the Mobile Router MR2 has already registered with it's HA the VAN prefixes as well as the care-of address it obtained from the visiting network. A packet from the server sent to the home IP address of the information panel will be intercepted by it's HA. At the HA, a route lookup on the information panel's IP address will hit the subnet route for the VAN prefix, telling the HA to tunnel the packet to MR2's care-of-address. MR2 receives the packet, decapsulates it, and sends it over the air interface to the information panel. Packets in the reverse direction travel a similar route (to overcome potential Ingress filtering restrictions  ), tunneled from MR2 via it's HA before being routed back to the Correspondent Node 1 . To illustrate the communication path in the case of nested mobile networks, consider a Correspondent Node (CN) that sends a packet to a mobile device in the passenger's PAN traveling within the aircraft's VAN. This operation of the nested mobility scenario is depicted in Figure 3 . Again, it is assumed that the PAN's MR (PMR) has registered the care-of address it obtained from MR2, with it's HA (HA-PMR). Furthermore as before MR2 has registered the VAN prefixes and the care-of address with it's HA (HA-MR2). A packet from a CN is initially addressed to the home address of the mobile device and gets routed to its home network (1). In the home network it is intercepted by the HA-PMR. A route lookup there indicates that the mobile node's prefix is at the VAN's care-of address. The HA-PMR then encapsulates and tunnels the packet to the VAN's care-of-address BIB001 . At the VAN's home network this gets intercepted by VAN Mobile Router's Home Agent HA-MR2. Its route lookup of the VAN's care-of-address determines that the packet needs to be encapsulated and tunneled yet again to the care-of-address in the network to which the VAN is currently attached (3). BIB002 The operation of this scenario is not shown in Figure 3 . When this doubly encapsulated packet reaches MR2, which recognizes the outer care-of address as its own strips it off to reveal the care-of-address of the PMR. It sends the packet to the PMR (4), which again recognizes the (only remaining) careof address as its own, strips it off, and sends the original packet to the mobile device in the PAN (5). Packets from the mobile device back to the CN traverse the same path in the reverse direction.