Chapter_4 new.pdf

Chapter 4 Network Layer A note on the use of these ppt slides: We’re making these slides freely available to all (faculty, students, readers). They’re in PowerPoint form so you see the animations; and can add, modify, and delete slides (including this one) and slide content to suit your needs. They...

Chapter 4 Network Layer A note on the use of these ppt slides: We’re making these slides freely available to all (faculty, students, readers). They’re in PowerPoint form so you see the animations; and can add, modify, and delete slides (including this one) and slide content to suit your needs. They obviously represent a lot of work on our part. In return for use, we only ask the following:  If you use these slides (e.g., in a class) that you mention their source (after all, we’d like people to use our book!)  If you post any slides on a www site, that you note that they are adapted from (or perhaps identical to) our slides, and note our copyright of this material. Computer Networking: A Top Down Approach 6th edition Jim Kurose, Keith Ross Addison-Wesley March 2012 Thanks and enjoy! JFK/KWR All material copyright 1996-2013 J.F Kurose and K.W. Ross, All Rights Reserved Network Layer 4-1 Chapter 4: outline 4.1 introduction 4.3 what’s inside a router 4.4 IP: Internet Protocol  datagram format  IPv4 addressing  IPv6 Network Layer 4-2 Network layer      transport segment from sending to receiving host on sending side encapsulates segments into datagrams on receiving side, delivers segments to transport layer network layer protocols in every host, router router examines header fields in all IP datagrams passing through it application transport network data link physical network data link physical network data link physical network data link physical network data link physical network data link physical network data link physical network data link physical network data link physical network data link physical network data link physical network data link physical application transport network data link physical Network Layer 4-3 Two key network-layer functions   forwarding: move packets from router’s input to appropriate router output routing: determine route taken by packets from source to dest.  routing algorithms analogy:   routing: process of planning trip from source to dest forwarding: process of getting through single interchange Network Layer 4-4 Interplay between routing and forwarding routing algorithm routing algorithm determines end-end-path through network local forwarding table header value output link forwarding table determines local forwarding at this router 0100 0101 0111 1001 3 2 2 1 value in arriving packet’s header 0111 1 3 2 Network Layer 4-5 Connection setup   3rd important function in some network architectures: before datagrams flow, two end hosts and intervening routers establish virtual connection  routers get involved  network vs transport layer connection service:  network: between two hosts (may also involve intervening routers in case of VCs)  transport: between two processes Network Layer 4-6 Chapter 4: outline 4.1 introduction 4.2 virtual circuit and datagram networks 4.3 what’s inside a router 4.4 IP: Internet Protocol     datagram format IPv4 addressing ICMP IPv6 4.5 routing algorithms  link state  distance vector  hierarchical routing 4.6 routing in the Internet  RIP  OSPF  BGP 4.7 broadcast and multicast routing Network Layer 4-7 Datagram networks  routers: no state about end-to-end connections  no network-level concept of “connection”  packets forwarded using destination host address application transport network 1. send datagrams data link physical application transport 2. receive datagrams network data link physical Network Layer 4-8 Datagram forwarding table routing algorithm local forwarding table dest address output link address-range 1 address-range 2 address-range 3 address-range 4 4 billion IP addresses, so rather than list individual destination address list range of addresses (aggregate table entries) 3 2 2 1 IP destination address in arriving packet’s header 1 3 2 Network Layer 4-9 Datagram forwarding table Destination Address Range Link Interface 11001000 00010111 00010000 00000000 through 11001000 00010111 00010111 11111111 0 11001000 00010111 00011000 00000000 through 11001000 00010111 00011000 11111111 1 11001000 00010111 00011001 00000000 through 11001000 00010111 00011111 11111111 2 otherwise 3 Q: but what happens if ranges don’t divide up so nicely? Network Layer 4-10 Chapter 4: outline 4.1 introduction 4.2 virtual circuit and datagram networks 4.3 what’s inside a router 4.4 IP: Internet Protocol     datagram format IPv4 addressing ICMP IPv6 4.5 routing algorithms  link state  distance vector  hierarchical routing 4.6 routing in the Internet  RIP  OSPF  BGP 4.7 broadcast and multicast routing Network Layer 4-11 Router architecture overview two key router functions:   run routing algorithms/protocol (RIP, OSPF, BGP) forwarding datagrams from incoming to outgoing link forwarding tables computed, pushed to input ports routing processor routing, management control plane (software) forwarding data plane (hardware) high-seed switching fabric router input ports router output ports Network Layer 4-12 Input port functions link layer protocol (receive) line termination lookup, forwarding switch fabric queueing physical layer: bit-level reception data link layer: e.g., Ethernet see chapter 5 decentralized switching:    given datagram dest., lookup output port using forwarding table in input port memory (“match plus action”) goal: complete input port processing at ‘line speed’ queuing: if datagrams arrive faster than forwarding rate into switch fabric Network Layer 4-13 Switching fabrics   transfer packet from input buffer to appropriate output buffer switching rate: rate at which packets can be transfer from inputs to outputs  often measured as multiple of input/output line rate  N inputs: switching rate N times line rate desirable  three types of switching fabrics memory memory bus crossbar Network Layer 4-14 Switching via memory first generation routers:  traditional computers with switching under direct control of CPU  packet copied to system’s memory  speed limited by memory bandwidth (2 bus crossings per datagram) input port (e.g., Ethernet) memory output port (e.g., Ethernet) system bus Network Layer 4-15 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 32 Gbps bus, Cisco 5600: sufficient speed for access and enterprise routers bus Network Layer 4-16 Switching via interconnection network     overcome bus bandwidth limitations banyan networks, crossbar, 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 60 Gbps through the interconnection network crossbar Network Layer 4-17 Output ports switch fabric datagram buffer queueing This slide in HUGELY important! link layer protocol (send) line termination buffering required when datagrams arrive Datagram (packets) can be lost from fabric faster than the transmission due to congestion, lack of buffers rate  scheduling discipline chooses among Priority scheduling – who queued gets best performance, network neutrality datagrams for transmission  Network Layer 4-18 Chapter 4: outline 4.1 introduction 4.2 virtual circuit and datagram networks 4.3 what’s inside a router 4.4 IP: Internet Protocol     datagram format IPv4 addressing ICMP IPv6 4.5 routing algorithms  link state  distance vector  hierarchical routing 4.6 routing in the Internet  RIP  OSPF  BGP 4.7 broadcast and multicast routing Network Layer 4-19 The Internet network layer host, router network layer functions: transport layer: TCP, UDP IP protocol routing protocols network layer addressing conventions datagram format packet handling conventions path selection RIP, OSPF, BGP forwarding table ICMP protocol error reporting router “signaling” link layer physical layer Network Layer 4-20 IP datagram format IP protocol version number header length (bytes) “type” of data max number remaining hops (decremented at each router) upper layer protocol to deliver payload to how much overhead?  20 bytes of TCP  20 bytes of IP  = 40 bytes + app layer overhead 32 bits total datagram length (bytes) ver head. type of len service length 16-bit identifier upper time to layer live fragment flgs offset header checksum for fragmentation/ reassembly 32 bit source IP address 32 bit destination IP address options (if any) data (variable length, typically a TCP or UDP segment) e.g. timestamp, record route taken, specify list of routers to visit. Network Layer 4-21 IP fragmentation, reassembly  fragmentation: in: one large datagram out: 3 smaller datagrams …  reassembly … network links have MTU (max.transfer size) largest possible link-level frame  different link types, different MTUs large IP datagram divided (“fragmented”) within net  one datagram becomes several datagrams  “reassembled” only at final destination  IP header bits used to identify, order related fragments Network Layer 4-22 IP fragmentation, reassembly example:   4000 byte datagram MTU = 1500 bytes 1480 bytes in data field offset = 1480/8 length ID fragflag =4000 =x =0 offset =0 one large datagram becomes several smaller datagrams length ID fragflag =1500 =x =1 offset =0 length ID fragflag =1500 =x =1 offset =185 length ID fragflag =1040 =x =0 offset =370 Network Layer 4-23 Chapter 4: outline 4.1 introduction 4.2 virtual circuit and datagram networks 4.3 what’s inside a router 4.4 IP: Internet Protocol     datagram format IPv4 addressing ICMP IPv6 4.5 routing algorithms  link state  distance vector  hierarchical routing 4.6 routing in the Internet  RIP  OSPF  BGP 4.7 broadcast and multicast routing Network Layer 4-24 IP addressing: introduction   IP address: 32-bit 223.1.1.1 identifier for host, router interface 223.1.1.2 interface: connection between host/router and physical link 223.1.2.1 223.1.1.4 223.1.3.27 223.1.1.3 223.1.2.2  router’s typically have multiple interfaces  host typically has one or two interfaces (e.g., wired Ethernet, wireless 802.11)  IP addresses associated with each interface 223.1.2.9 223.1.3.1 223.1.3.2 223.1.1.1 = 11011111 00000001 00000001 00000001 223 1 1 1 Network Layer 4-25 IP addressing: introduction Q: how are interfaces actually connected? A: we’ll learn about that in chapter 5, 6. 223.1.1.1 223.1.2.1 223.1.1.2 223.1.1.4 223.1.1.3 223.1.2.9 223.1.3.27 223.1.2.2 A: wired Ethernet interfaces connected by Ethernet switches 223.1.3.1 For now: don’t need to worry about how one interface is connected to another (with no intervening router) 223.1.3.2 A: wireless WiFi interfaces connected by WiFi base station Network Layer 4-26 Subnets  IP address: subnet part - high order bits host part - low order bits  what ’s a subnet ? device interfaces with same subnet part of IP address can physically reach each other without intervening router 223.1.1.1 223.1.1.2 223.1.1.4 223.1.2.1 223.1.2.9 223.1.2.2 223.1.1.3 223.1.3.27 subnet 223.1.3.1 223.1.3.2 network consisting of 3 subnets Network Layer 4-27 Subnets 223.1.1.0/24 223.1.2.0/24 recipe  to determine the subnets, detach each interface from its host or router, creating islands of isolated networks  each isolated network is called a subnet 223.1.1.1 223.1.1.2 223.1.1.4 223.1.2.1 223.1.2.9 223.1.2.2 223.1.1.3 223.1.3.27 subnet 223.1.3.1 223.1.3.2 223.1.3.0/24 subnet mask: /24 Network Layer 4-28 Subnets 223.1.1.2 how many? 223.1.1.1 223.1.1.4 223.1.1.3 223.1.9.2 223.1.7.0 223.1.9.1 223.1.7.1 223.1.8.1 223.1.8.0 223.1.2.6 223.1.2.1 223.1.3.27 223.1.2.2 223.1.3.1 223.1.3.2 Network Layer 4-29 IP addressing: CIDR CIDR: Classless InterDomain Routing  subnet portion of address of arbitrary length  address format: a.b.c.d/x, where x is # bits in subnet portion of address subnet part host part 11001000 00010111 00010000 00000000 200.23.16.0/23 Network Layer 4-30 IP addresses: how to get one? Q: How does a host get IP address?  hard-coded by system admin in a file  Windows: control-panel->network->configuration>tcp/ip->properties  UNIX: /etc/rc.config  DHCP: Dynamic Host Configuration Protocol: dynamically get address from as server  “plug-and-play” Network Layer 4-31 DHCP: Dynamic Host Configuration Protocol goal: allow host to dynamically obtain its IP address from network server when it joins network  can renew its lease on address in use  allows reuse of addresses (only hold address while connected/“on”)  support for mobile users who want to join network (more shortly) DHCP overview:     host broadcasts “DHCP discover” msg [optional] DHCP server responds with “DHCP offer” msg [optional] host requests IP address: “DHCP request” msg DHCP server sends address: “DHCP ack” msg Network Layer 4-32 DHCP client-server scenario DHCP server 223.1.1.0/24 223.1.2.1 223.1.1.1 223.1.1.2 223.1.1.4 223.1.1.3 223.1.2.9 223.1.3.27 223.1.2.2 arriving DHCP client needs address in this network 223.1.2.0/24 223.1.3.2 223.1.3.1 223.1.3.0/24 Network Layer 4-33 DHCP client-server scenario DHCP server: 223.1.2.5 DHCP discover src : 0.0.0.0, 68 arriving client Broadcast: is there a dest.: 255.255.255.255,67 DHCPyiaddr: server0.0.0.0 out there? transaction ID: 654 DHCP offer src: 223.1.2.5, 67 Broadcast: I’m a DHCP dest: 255.255.255.255, 68 yiaddrr: 223.1.2.4 server! Here’s an IP transaction 654 use address youID:can lifetime: 3600 secs DHCP request src: 0.0.0.0, 68 dest:: 255.255.255.255, 67 Broadcast: OK. I’ll take yiaddrr: 223.1.2.4 that IP address! transaction ID: 655 lifetime: 3600 secs DHCP ACK src: 223.1.2.5, 67 dest: 255.255.255.255, 68 Broadcast: OK. You’ve yiaddrr: 223.1.2.4 got that IPID: address! transaction 655 lifetime: 3600 secs Network Layer 4-34 Chapter 4: outline 4.1 introduction 4.3 what’s inside a router 4.4 IP: Internet Protocol  datagram format  IPv4 addressing  IPv6 4.5 routing algorithms  link state  distance vector  hierarchical routing 4.6 routing in the Internet  RIP  OSPF  BGP 4.7 broadcast and multicast routing Network Layer 4-35 IPv6: motivation   initial motivation: 32-bit address space soon to be completely allocated. additional motivation:  header format helps speed processing/forwarding  header changes to facilitate QoS IPv6 datagram format:  fixed-length 40 byte header  no fragmentation allowed Network Layer 4-36 IPv6 datagram format 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 ver pri flow label hop limit payload len next hdr source address (128 bits) destination address (128 bits) data 32 bits Network Layer 4-37 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 4-38