Transcript Mobility
Router Architecture Overview Two key router functions: run routing algorithms/protocol (RIP, OSPF, BGP) switching datagrams from incoming to outgoing link Network Layer 4-1 Input Port Functions Physical layer: bit-level reception Data link layer: e.g., Ethernet see chapter 5 Decentralized switching: given datagram dest., lookup output port using routing table in input port memory goal: complete input port processing at ‘line speed’ queuing: if datagrams arrive faster than forwarding rate into switch fabric Network Layer 4-2 Input Port Queuing Fabric slower that input ports combined -> queueing may occur at input queues Head-of-the-Line (HOL) blocking: queued datagram at front of queue prevents others in queue from moving forward queueing delay and loss due to input buffer overflow! Network Layer 4-3 Three types of switching fabrics Network Layer 4-4 Switching Via Memory First generation routers: packet copied by system’s (single) CPU speed limited by memory bandwidth (2 bus crossings per datagram) Input Port Memory Output Port System Bus Modern routers: input port processor performs lookup, copy into memory Cisco Catalyst 8500 Network Layer 4-5 Switching Via a Bus datagram from input port memory to output port memory via a shared bus bus contention: switching speed limited by bus bandwidth 1 Gbps bus, Cisco 1900: sufficient speed for access and enterprise routers (not regional or backbone) Network Layer 4-6 Switching Via An Interconnection Network overcome bus bandwidth limitations Banyan networks, other interconnection nets initially developed to connect processors in multiprocessor Advanced design: fragmenting datagram into fixed length cells, switch cells through the fabric. Cisco 12000: switches Gbps through the interconnection network Network Layer 4-7 Output Ports Buffering required when datagrams arrive from fabric faster than the transmission rate Scheduling discipline chooses among queued datagrams for transmission Network Layer 4-8 Output port queueing buffering when arrival rate via switch exceeds output line speed queueing (delay) and loss due to output port buffer overflow! Network Layer 4-9 IPv6 Initial motivation: 32-bit address space completely allocated by 2008. Additional motivation: header format helps speed processing/forwarding header changes to facilitate QoS new “anycast” address: route to “best” of several replicated servers IPv6 datagram format: fixed-length 40 byte header no fragmentation allowed Network Layer 4-10 IPv6 Header (Cont) Priority: identify priority among datagrams in flow Flow Label: identify datagrams in same “flow” (concept of “flow” not well defined). Next header: identify upper layer protocol for data Network Layer 4-11 Other Changes from IPv4 Checksum: removed entirely to reduce processing time at each hop Options: allowed, but outside of header, indicated by “Next Header” field ICMPv6: new version of ICMP additional message types, e.g. “Packet Too Big” multicast group management functions Network Layer 4-12 Transition From IPv4 To IPv6 Not all routers can be upgraded simultaneous no “flag days” How will the network operate with mixed IPv4 and IPv6 routers? Two proposed approaches: Dual Stack: some routers with dual stack (v6, v4) can “translate” between formats Tunneling: IPv6 carried as payload in IPv4 datagram among IPv4 routers Network Layer 4-13 Dual Stack Approach A B C D E F IPv6 IPv6 IPv4 IPv4 IPv6 IPv6 Flow: X Src: A Dest: F Src:A Dest: F Src:A Dest: F Flow: ?? Src: A Dest: F data data data data B-to-C: IPv4 B-to-C: IPv4 B-to-C: IPv6 A-to-B: IPv6 Network Layer 4-14 Tunneling Logical view: Physical view: A B IPv6 IPv6 A B C IPv6 IPv6 IPv4 Flow: X Src: A Dest: F data A-to-B: IPv6 E F IPv6 IPv6 D E F IPv4 IPv6 IPv6 tunnel Src:B Dest: E Src:B Dest: E Flow: X Src: A Dest: F Flow: X Src: A Dest: F data data B-to-C: IPv6 inside IPv4 B-to-C: IPv6 inside IPv4 Flow: X Src: A Dest: F data E-to-F: IPv6 Network Layer 4-15 What is mobility? spectrum of mobility, from the network perspective: no mobility mobile user, using same access point high mobility mobile user, connecting/ disconnecting from network using DHCP. mobile user, passing through multiple access point while maintaining ongoing connections (like cell phone) Network Layer 4-16 Mobility: Vocabulary home network: permanent “home” of mobile (e.g., 128.119.40/24) Permanent address: address in home network, can always be used to reach mobile e.g., 128.119.40.186 home agent: entity that will perform mobility functions on behalf of mobile, when mobile is remote wide area network correspondent Network Layer 4-17 Mobility: more vocabulary Permanent address: remains constant (e.g., 128.119.40.186) visited network: network in which mobile currently resides (e.g., 79.129.13/24) Care-of-address: address in visited network. (e.g., 79,129.13.2) wide area network correspondent: wants to communicate with mobile home agent: entity in visited network that performs mobility functions on behalf of mobile. Network Layer 4-18 How do you contact a mobile friend: Consider friend frequently changing addresses, how do you find her? I wonder where Alice moved to? search all phone books? call her parents? expect her to let you know where he/she is? Network Layer 4-19 Mobility: approaches Let routing handle it: routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange. routing tables indicate where each mobile located no changes to end-systems Let end-systems handle it: indirect routing: communication from correspondent to mobile goes through home agent, then forwarded to remote direct routing: correspondent gets foreign address of mobile, sends directly to mobile Network Layer 4-20 Mobility: approaches Let routing handle it: routers advertise permanent not address of mobile-nodes-in-residence via usual scalable routing table exchange. to millions of routing tables indicate mobiles where each mobile located no changes to end-systems let end-systems handle it: indirect routing: communication from correspondent to mobile goes through home agent, then forwarded to remote direct routing: correspondent gets foreign address of mobile, sends directly to mobile Network Layer 4-21 Mobility: registration visited network home network 2 1 wide area network foreign agent contacts home agent home: “this mobile is resident in my network” mobile contacts foreign agent on entering visited network End result: Foreign agent knows about mobile Home agent knows location of mobile Network Layer 4-22 Mobility via Indirect Routing foreign agent receives packets, forwards to mobile home agent intercepts packets, forwards to foreign agent home network visited network 3 wide area network correspondent addresses packets using home address of mobile 1 2 4 mobile replies directly to correspondent Network Layer 4-23 Indirect Routing: comments Mobile uses two addresses: permanent address: used by correspondent (hence mobile location is transparent to correspondent) care-of-address: used by home agent to forward datagrams to mobile foreign agent functions may be done by mobile itself triangle routing: correspondent-home-networkmobile inefficient when correspondent, mobile are in same network Network Layer 4-24 Forwarding datagrams to remote mobile foreign-agent-to-mobile packet packet sent by home agent to foreign agent: a packet within a packet dest: 79.129.13.2 dest: 128.119.40.186 dest: 128.119.40.186 Permanent address: 128.119.40.186 dest: 128.119.40.186 Care-of address: 79.129.13.2 packet sent by correspondent Network Layer 4-25 Indirect Routing: moving between networks suppose mobile user moves to another network registers with new foreign agent new foreign agent registers with home agent home agent update care-of-address for mobile packets continue to be forwarded to mobile (but with new care-of-address) Mobility, changing foreign networks transparent: on going connections can be maintained! Network Layer 4-26 Mobility via Direct Routing correspondent forwards to foreign agent foreign agent receives packets, forwards to mobile home network 4 wide area network 2 correspondent requests, receives foreign address of mobile visited network 1 3 4 mobile replies directly to correspondent Network Layer 4-27 Mobility via Direct Routing: comments overcome triangle routing problem non-transparent to correspondent: correspondent must get care-of-address from home agent What happens if mobile changes networks? Network Layer 4-28 Mobile IP RFC 3220 has many features we’ve seen: home agents, foreign agents, foreign-agent registration, care-of-addresses, encapsulation (packet-within-a-packet) three components to standard: agent discovery registration with home agent indirect routing of datagrams Network Layer 4-29 Mobile IP: agent discovery agent advertisement: foreign/home agents advertise service by broadcasting ICMP messages (typefield = 9) 0 type = 9 24 checksum =9 code = 0 =9 H,F bits: home and/or foreign agent R bit: registration required 16 8 standard ICMP fields router address type = 16 length registration lifetime sequence # RBHFMGV bits reserved 0 or more care-ofaddresses mobility agent advertisement extension Network Layer 4-30 Mobile IP: registration example home agent HA: 128.119.40.7 foreign agent COA: 79.129.13.2 visited network: 79.129.13/24 ICMP agent adv. COA: 79.129.13.2 …. registration req. COA: 79.129.13.2 HA: 128.119.40.7 MA: 128.119.40.186 Lifetime: 9999 identification: 714 encapsulation format …. Mobile agent MA: 128.119.40.186 registration req. COA: 79.129.13.2 HA: 128.119.40.7 MA: 128.119.40.186 Lifetime: 9999 identification:714 …. registration reply time HA: 128.119.40.7 MA: 128.119.40.186 Lifetime: 4999 Identification: 714 encapsulation format …. registration reply HA: 128.119.40.7 MA: 128.119.40.186 Lifetime: 4999 Identification: 714 …. Network Layer 4-31 Network Layer: summary What we’ve covered: network layer services routing principles: link state and distance vector hierarchical routing addressing IP Internet routing protocols RIP, OSPF, BGP what’s inside a router? IPv6 mobility Next stop: the Data link layer! Network Layer 4-32