Mobility. Why (and How) Things Move. MulT- Homing. Physical Mobility. MigraTon. Failover. Jennifer Rexford COS 461: Computer Networks

Transcription

1 Mobility Why (and How) Things Move Jennifer Rexford COS 461: Computer Networks Lectures: MW 10-10:50am in Architecture N101 hhp:// Physical Mobility MulT- Homing WiFi 3G Device ahaches to a new ahachment point Device starts using a different ahachment point 3 4 MigraTon Failover Process or virtual machine migraton Backup machine takes over axer the primary fails 5 6 1

2 Change Address of Mobile Node? Handling Mobility A link session B name address a path? 7 8 Keeping the Address the Same Changing the Address a path A link session B name a b Mobility is a rou$ng problem Change the routes to reach the new locaton Challenge: scalability of the routng protocol Mobility is a directory problem Change the mapping of name to address Challenge: scalability of directory, updatng neighbor 9 10 Two Internet Design Decisions Socket abstracton ConnecTon between a pair of fixed IP addresses and port numbers Leads to more emphasis on routng solutons Interface addresses Addresses refer to interfaces (adaptors) Not the host, or the service WiFi RouTng SoluTons Address Stays the Same G 11 1

3 Three Examples Ethernet MAC learning of the new locaton IP routng Inject IP address(es) at new locaton Mobile IP StaTonary home agent directs traffic to new locaton Example #1: Ethernet a MAC learning Learn s locaton when sends a frame SoX state: Tmeout the cached informaton Making Larger Ethernet Segments Ethernet handles mobility IP address and MAC address stay the same Switches learn to route to the new locaton But, larger s have multple segments Cannot retain your IP address as you move SoluTon: virtual local area s (VLAN) Logical Ethernet segment spanning a campus E.g., interconnectng the WiFi access points Seamless mobility, no changes to hosts or apps No changes to MAC or IP addresses Ethernet does not scale Long paths, state per MAC address, flooding, Widely used approach in campus s Example #: IP RouTng Boeing Connexion: Wide- Area Mobility Node has a persistent address (e.g., ) Injected into routng protocol (e.g., OSPF) /4 BGP / / abstracts.php?pt=ntk1jm5hbm9nmze=&nm=nanog

4 Seamless mobility, no MAC or IP address changes Traffic follows an efficient path to new locaton Does not scale to large number of mobile hosts More routng- protocol messages Larger routng tables to store smaller address blocks Example #3: Mobile IP Home : permanent home of mobile (e.g., /4) Permanent address: can always be used to reach mobile, e.g., Home agent: performs mobility functions on behalf of mobile Correspondent: wants to communicate with mobile correspondent 19 0 Visited Network and Care- of Address Permanent address: remains constant (e.g., ) Correspondent Care-of-address: in visited (e.g., 79,19.13.) Visited : e.g., /4 Foreign agent: performs mobility functions for the mobile. 1 Mobility: RegistraTon home foreign agent contacts home agent home: this mobile is resident in my visited Foreign agent knows about mobile Home agent knows locaton of mobile 1 mobile contacts foreign agent on entering visited home Mobility via Indirect RouTng correspondent addresses packets using home address of mobile home agent intercepts packets, forwards to foreign agent 1 foreign agent receives packets, forwards to mobile 4 3 visited mobile replies directly to correspondent Seamless to the remote end- point No routng- protocol overhead Overhead of running home and foreign agents Inefficient triangle routng (high stretch ) Foreign agent sends spoofed IP source address 3 4 4

5 Directory SoluTons Change the mapping of name to address Three Examples Ethernet Gratuitous ARP to change the MAC address associated with an IP address Dynamic DNS DNS updates to change the IP address(es) associated with a domain name Various recent proposed designs UpdaTng the remote end- point (e.g., end host, edge switch) to use a new address 5 6 Example #1: Ethernet MAC m1 Ethernet MulT- Homing MAC m1 Backup machine floods gratuitous ARP response Associates the IP address with a new MAC address Hosts update their ARP cache MAC m Gratuitous ARP Balance traffic over two interfaces MAC m Fail over from one interface to the other 7 8 Seamless change from one MAC address to another Works only within a single Ethernet subnet Scalability limitatons of Ethernet Example #: Dynamic DNS Name: IP: Name: IP: Used in data- center s But doesn t help with smart phones homed to multple administratve domains 9 Dynamically update DNS Change the mapping of domain name to IP address Future DNS requests get the new addres 30 5

6 ApplicaTons of Dynamic DNS Replicated services Direct future requests to a different replica E.g., for failover, load balancing, performance, etc. Services on dynamically- assigned IP addresses ResidenTal user with a dynamic IP address Directs clients to the server s current address Fast flux in botnets Hiding phishing and malware delivery servers behind constantly changing IP addresses No new infrastructure Leverages existng DNS servers Only helps for new connectons Overheads of updatng DNS servers Stymied by DNS caching 31 3 Example #3: UpdaTng the End- Points UpdaTng the Edge Switches Mobile node updates the remote end- point Sends the remote end- point the new IP address Allowing ongoing connecton to contnue Can be used in conjuncton with Dynamic DNS Update the switches Hosts retain their addresses Switches rewrite the addresses, or encapsulate Used in some data- center s Mobility Today Scalability of hierarchical addressing Efficiency of routng along short paths Changes to the end host (e.g., apps, TCP, etc.) or support from the edge switches Difficulty when both end- points move at once Work in progress Used in some data centers, recent standards/projects Limited support for mobility E.g., within a single Ethernet subnet E.g., among base statons on a campus ApplicaTons increasingly robust to mobility Robust to changes in IP address, and disconnectons E.g., e- mail client contactng the e- mail server and allowing reading/writng while disconnected

7 Mobility Tomorrow Increasing demand for seamless IP mobility E.g., contnue a VoIP call while on the train E.g., virtual machine migraton within and between data centers Increasing integraton of WiFi and cellular E.g., mult- homed cell phones that can use both s E.g., servers with multple interface cards Need beher mobility & mult- homing solutons! Conclusions Mobility Change is hard RouTng and directory solutons Mobility is stll a moving target Friday s precept: IP routers and assignment # Midterm next week Midterm next Wednesday during lecture Tme In Frist 30, not in the lecture hall