CSE 123bCSE 123bCommunications SoftwareCommunications SoftwareSpring 2004Spring 2004Lecture 9: Mobile NetworkingLecture 9: Mobile NetworkingStefan SavageStefan SavageMay 9, 2004 CSE 123b -- Lecture 8 – IP Multicast 2Quick announcementsQuick announcementsz Typo in problem #1 of HW #2 (fixed as of 1pm yesterday)z Please consider chapter 4.3-4.3.3 to be part of the assigned reading for the midterm (this was the reading related to Inter-domain routing)May 9, 2004 CSE 123b -- Lecture 8 – IP Multicast 3Last classLast classz Multicast communications◆ One-to-many◆ Publish and subscribe model (receiver-based)z Routing protocols◆ Per-source tree routing» RPF, RPB, RPM» Builds Efficient trees» S*G state explosion for large networks/groups◆ Shared tree» Unicast to rendezvous point» More complex, fragile, hard to manage» Trees inefficient by as much as 2x» Only requires G state on routersMay 9, 2004 CSE 123b -- Lecture 8 – IP Multicast 4Today’s issuesToday’s issuesz What are implications of hosts that move?◆ Remember routing? It doesn’t work anymore…z Problem reviewz Design issuesz Case studies◆ Mobile IP [Johnson96]◆ TCP Migrate [Snoeren et al00]May 9, 2004 CSE 123b -- Lecture 8 – IP Multicast 5The Mobility ProblemThe Mobility Problemz Implicit assumption that Internet hosts are fixed◆ IP routing breaks if addresses change location. Why?z Unfortunately, the buying public likes mobilityMay 9, 2004 CSE 123b -- Lecture 8 – IP Multicast 6ProblemsProblemsz How does a mobile host get a local IP address?z How do you know which IP address to use when sending to a mobile host?z If a host moves during communication how do you know how to migrate state to the new IP address?z Backwards compatibility (higher-layer state caching)May 9, 2004 CSE 123b -- Lecture 8 – IP Multicast 7Application demandsApplication demandsz Geographic scope◆ Switching 802.11 LANs at UCSD vs visiting IBM in Zurichz Rate of change ◆ Cell-phone in airplane vs hotel room dialinz Continuity◆ State associated with session (e.g. ordering plane tickets)z Interactivity◆ Cell-phone handoff?z Remote accessibility◆ Client vs ServerMay 9, 2004 CSE 123b -- Lecture 8 – IP Multicast 8Some simple solutionsSome simple solutionsz Datalink layer mobility◆ Wireless learning bridges (CMU campus solution)◆ Transparently update MAC-layer mappings in access points◆ Pro: transparent to all higher layers◆ Con: Local scope onlyz Dynamic Host Configuration Protocol (DHCP)◆ Request IP address dynamically (special broadcast address)◆ How do you get contacted at new IP address?» One solution: dynamic DNS◆ Authentication issues (who can use 802.11 in AP&M?)◆ Pro: Great over longer time scales… ◆ Con: What happens if you move during a session?May 9, 2004 CSE 123b -- Lecture 8 – IP Multicast 9Mobile IP: Johnson96Mobile IP: Johnson96z Current IETF proposed standard for mobility◆ Dates back to research in the early 90s◆ IPv4 (RFC 2002), IPv6 version is roughly the samez Design constraints◆ Network layer solution◆ Only requires changes to mobile hosts◆ Stationary hosts oblivious to mobility◆ Incrementally deployableMay 9, 2004 CSE 123b -- Lecture 8 – IP Multicast 10Mobile IP ApproachMobile IP Approachz Mobile Host (MH) has two addressesz Home address ◆ Never changes, uniquely identifies the host◆ In “home network”◆ Correspondent host (CH) addresses all packets to the home addressz Care-of address ◆ Will change, perhaps frequently◆ In “foreign network”◆ Related to current location (IP routing gets it to the right place)May 9, 2004 CSE 123b -- Lecture 8 – IP Multicast 11Home and Foreign AgentsHome and Foreign Agentsz Home agent (HA) implements level of indirection between the mobile host and correspondents◆ Accepts traffic sent to home address» What about requests from home network?◆ Tunnels traffic to the mobile host (using care-of address)◆ And vice versa, correspondent none the wiserz Foreign agent (FA) represents mobile in foreign network◆ Foreign agent can be care-of address» Mobile host does not need its own address in foreign network» Potential advantage: deal with local mobility locallyMay 9, 2004 CSE 123b -- Lecture 8 – IP Multicast 12Mobile IP (MH at Home)Mobile IP (MH at Home)Mobile Host (MH)Visiting LocationHomeInternetCorrespondent Host (CH)PacketHome Agent (HA)May 9, 2004 CSE 123b -- Lecture 8 – IP Multicast 13Mobile IP (MH Moving)Mobile IP (MH Moving)Visiting LocationHomeInternetCorrespondent Host (CH)PacketMobile Host (MH)MH is nowwith meHome Agent (HA)Foreign Agent (FA)RegisterMay 9, 2004 CSE 123b -- Lecture 8 – IP Multicast 14Mobile IP (MH Away)Mobile IP (MH Away)Visiting LocationHomeInternetCorrespondent Host (CH)PacketEncapsulatedMobile Host (MH)Home Agent (HA)Foreign Agent (FA)May 9, 2004 CSE 123b -- Lecture 8 – IP Multicast 15Mobile IP IssuesMobile IP Issuesz To make all this happen, a number of issues have to be addressed◆ Discovering agents◆ Registering addresses with agents (establishing bindings)◆ Authentication◆ Tunneling◆ Performance (!)May 9, 2004 CSE 123b -- Lecture 8 – IP Multicast 16Agent DiscoveryAgent Discoveryz Agent discovery enables a mobile host◆ To notice when it changes networks◆ To notice when it is home again» When home, take down the tunnel◆ To find a foreign agent to register withz Agents multicast agent advertisements locally◆ Beacons that tell the mobile who it can hear◆ Start in network A, move to network B◆ Lack of A’s beacons and presence of B’s tells mobile it has switched networksz Mobile can also multicast an agent solicitationz Why does multicast work here?May 9, 2004 CSE 123b -- Lecture 8 – IP Multicast 17RegistrationRegistrationz Mobiles must register care-of addresses with their home agents◆ So that the home agent knows where to tunnel packets◆ Registration needs to be updated when location changesz Multiple steps◆ Registration requests first go to foreign agent, then to home agent, which replies to foreign agent, which forwards back to the mobilez Lifetimes◆ Registrations have TTLsMay 9, 2004 CSE 123b -- Lecture 8 – IP Multicast 18Registration AuthenticationRegistration Authenticationz Registration requests can be used by attackers to hijack tunnels from home agent◆ Hey, send all the mobile’s traffic to me nowz Need to authenticate that a registration◆ Came from mobile host (authenticity)◆ Has not been altered (integrity)◆ Is