1 OverviewOverview A device on a network is reachable through normal IP routing by the IP address it is assigned on the network. The problem occurs when a device roams away from its home network and is no longer reachable using normal IP address. This results in the active sessions of the device being terminated.

2 Mobile IP Mobile IP aims to provide for seamless relocation by providing services to mobile users as if they were at their home network. It is an open std defined by IETF that allows users to keep same IP address and maintain ongoing application while roaming between IP networks.

3 OverviewOverview Mobile IP was created to enable users to keep the same IP address while traveling to a different network, thus ensuring that a roaming individual could continue communication without sessions being dropped Because the mobility functions of Mobile IP are performed at the network layer rather than the physical layer, the mobile device can span different types of wireless and Wireline networks while maintaining connections and ongoing applications

4 Applications of mobile IP Remote login, remote printing and file transfers Uninterrupted communication while an individual roams across network boundaries. Mobile IP technology is embedded in the functionality of packet equipment for 2.5G and 3G2.5G3G For example, GPRS depends on mobile IP to enable the relay of messages to a GPRS phone via the SGSN from the GGSN without the sending needing to know the serving node IP address.GPRS

5 Mobile IP: An Emerging Standard Features of Mobile IP:  Separates “location” from “address”.  No new IP addresses or address formats required.  Only “mobile aware” routers and mobile units need new software. Other routers and hosts use current IP. Impact of Mobile IP on users:  Can take any computer to any location; routing of communications from correspondents is done “automatically”.  Services provided as if at home network.

6 Effect of Mobility on Protocol Stack Application: new applications and adaptations Transport: congestion and flow control Network: addressing and routing Link: media access and handoff Physical: transmission errors and interference

7 Routing and Mobility Finding a path from a source to a destination Issues  Frequent route changes  Route changes may be related to host movement  Low bandwidth links Goal of routing protocols  decrease routing-related overhead  find short routes  find “stable” routes (despite mobility)

8 Mobile IP (RFC 3344): Motivation Traditional routing  based on IP address; network prefix determines the subnet  change of physical subnet implies –change of IP address (conform to new subnet), or –special routing table entries to forward packets to new subnet

9 Mobile IP motivation Changing of IP address  DNS updates take to long time  TCP connections break  security problems Changing entries in routing tables  does not scale with the number of mobile hosts and frequent changes in the location  security problems

10 Mobile IP: Basic Idea Router 1 Router 3 Router 2 S MN Home agent

11 Mobile IP: Basic Idea Router 1 Router 3 Router 2 SMN Home agent Foreign agent move Packets are tunneled using IP in IP

12 Components of a Mobile IP network Mobile IP has the following components: Mobile Node (MN): node that moves across networks without changing its IP address. Such as PDA, laptop, electronic books etc. whose software enables network roaming capabilities. Home Agent (HA):It is a router on the home network (HN) serving as an anchor point for communication with the mobile node. Registers the location of the MN, tunnels IP packets to the COA

13 Components of a Mobile IP network Foreign Agent (FA): It is a router that may function as the point of attachment for the MN when it roams to a foreign network (FN), delivering packets from the HA to the MN. Correspondent Node (CN): HA tunnels packets from a device on the Internet, called a Correspondent Node (CN), to the roaming MN. A tunnel is established between the HA and a reachable point for the MN in the FN.

14 Correspondent node Correspondent node is a host that wants to send packets to the mobile host Correspondent node sends packets to the mobile host’s IP permanent address These packets are routed to the mobile host’s home network Home agent forwards IP packets for mobile host to current care-of address Mobile host sends packets directly to correspondent, using permanent home IP as source IP

15 Mobile IP: Basics, Cont. Home Agent Correspondent Node

16 Components of a Mobile IP network The care-of address: It is the termination point of the tunnel toward the MN when it is on a foreign network.  address of the current tunnel end-point for the MN (at FA or MN)  actual location of the MN from an IP point of view The HA maintains an association between the home IP address of the MN and its care-of address, which is the current location of the MN on the foreign or visited network

17 Different entities of Mobile IP

18 Data transfer to the mobile system Internet sender FA HA MN home network foreign network receiver Sender sends to the IP addr of MN, HA intercepts packet (proxy ARP) 2. HA tunnels packet to COA, here FA, by encapsulation 3. FA forwards the packet to the MN CN

19 Data transfer from the mobile system Internet receiver FA HA MN home network foreign network sender 1 1. Sender sends to the IP address of the receiver as usual, FA works as default router CN

20 How Mobile IP works Mobile IP process has three main phases, which are: Agent Discovery (agent advertisement) A MN discovers its FA and HA during agent discovery. Registration The MN registers its current location with the FA and HA during registration. Tunneling A reciprocal tunnel is set up by the HA to the care-of address (current location of the MN on the FN) to route packets to the MN as it roams.

21 Mobile IP: How It Works Mobile unit registers with the foreign network upon arrival. Home Agent and Foreign Agent cooperate to deliver IP datagrams to the mobile unit.  forwarding caches at both agents  IP-in-IP encapsulation Mobile unit deregisters (explicitly or implicitly) upon leaving foreign network.

22 EncapsulationEncapsulation original IP headeroriginal data new datanew IP header outer headerinner headeroriginal data

23 The Home Agent and Foreign Agent continuously advertise their services on the network through an Agent Discovery process, enabling the Home Agent to recognize when a new Foreign Agent is aquired and allowing the Mobile Node to register a new Care of Address.

24 Agent Advertisement HA/FA periodically send advertisement messages into their physical subnets. During the agent discovery phase, the HA and FA advertise their services on the network by using the ICMP Router Discovery Protocol (IRDP). The MN listens to these advertisements to determine if it is connected to its home network or foreign network. MN listens to these messages and detects, if it is in home/foreign network The IRDP advertisements carry Mobile IP extensions that specify whether an agent is a HA, FA, or both; its care-of address; the types of services it will provide such as reverse tunneling and generic routing encapsulation (GRE). MN reads a Care-of-address from the FA advertisement messages

25 Agent advertisement preference level 1 router address 1 #addresses type addr. sizelifetime checksum COA 1 COA 2 typesequence numberlength code preference level 2 router address 2... registration lifetime... RBHFMGV reserved

26 Agent Discovery Rather than waiting for agent advertisements, a MN can send out an agent solicitation. This solicitation forces any agents on the link to immediately send an agent advertisement. If a MN determines that it is connected to a foreign network, it acquires a care-of address. Two types of care-of addresses exist: Care-of address acquired from a FA Colocated care-of address

27 Mobile IP: Care-of Addresses Whenever a mobile host connects to a remote network, two choices:  care-of can be the address of a foreign agent on the remote network –foreign agent delivers packets forwarded from home agent to mobile host  care-of ( collocated) can be a temporary, foreign IP address obtained through, e.g., DHCP –home agent tunnels packets directly to the temporary IP address Regardless, care-of address must be registered with home agent

28 Registration The MN is configured with the IP address and mobility security association of its HA The MN uses this information along with the information that it learns from the FA advertisements to form a Mobile IP registration request. It adds the registration request to its pending list and sends the registration request to its HA either through the FA care-of address directly if it is using a colocated care-of address

29 Registration The HA checks the validity of the registration request, which includes authentication of the MN. If the registration request is valid, the HA creates a mobility binding a tunnel to the care-of address, and a routing entry for forwarding packets to the home address through the tunnel.

30 Registration The HA then sends a registration reply to the MN through the FA (if the registration request was received via the FA) or directly to the MN. If the registration request is not valid, the HA rejects the request by sending a registration reply with an appropriate error code.

31 Registration The FA checks the validity of the registration reply, including ensuring that an associated registration request exists in its pending list. If the registration reply is valid, the FA adds the MN to its visitor list, establishes a tunnel to the HA, and creates a routing entry for forwarding packets to the home address. It then relays the registration reply to the MN.

32 Registration Finally, the MN checks the validity of the registration reply, which includes ensuring an associated request is in its pending list as well as proper authentication of the HA. If the registration reply is not valid, the MN discards the reply. If a valid registration reply specifies that the registration is accepted, the MN is confirmed that the mobility agents are aware of its roaming. In the colocated care-of address case, it adds a tunnel to the HA. Subsequently, it sends all packets to the FA.

33 RegistrationRegistration t MN HA registration request registration reply t MN FAHA registration request registration request registration reply registration reply

34 Tunneling Data packets addressed to the MN are routed to its home network, where the HA now intercepts and tunnels them to the care-of address toward the MN. Tunneling has two primary functions: (i) Encapsulation of the data packet to reach the tunnel endpoint, and (ii) Decapsulation when the packet is delivered at that endpoint. The default tunnel mode is IP Encapsulation within IP Encapsulation.

35 TunnelingTunneling HA tells local nodes and routers to send MN’s datagrams to it HA intercepts datagrams intended for MN, then encapsulates and forwards them to MN’s care-of address FA receives encapsulated datagrams, then decapsulates them and delivers them to MN datagram payload IP header To: mobile node IP header To: care-of address

36 IP header IP-in-IP Tunneling Packet to be forwarded is encapsulated in a new IP packet In the new header:  Destination = care-of-address  Source = address of home agent  Protocol number = IP-in-IP IP header data IP header data

37 Tunneling

38 Reverse Tunneling However, this data path is topologically incorrect because it does not reflect the true IP network source for the data— rather, it reflects the home network of the MN. Because the packets show the home network as their source inside a foreign network, an access control list on routers in the network called ingress filtering drops the packets instead of forwarding them. A feature called reverse tunneling solves this problem by having the Foreign Agent tunnel packets back to the Home Agent when it receives them from the Mobile Node. See Figure next page

39 Reverse tunneling

40 Mobile IP: Routing