Chapter 4: network layer chapter goals so understand principles behind network layer services. network layer service models forwarding versus routing how a router works routing(path selection) broadcast multicast ,s instantiation implementation in the internet Network Layer 4-2
Network Layer 4-2 Chapter 4: network layer chapter goals: ❖ understand principles behind network layer services: ▪ network layer service models ▪ forwarding versus routing ▪ how a router works ▪ routing (path selection) ▪ broadcast, multicast ❖ instantiation, implementation in the Internet
Chapter 4: outline 4.1 introduction 4.5 routing algorithms 4.2 virtual circuit and link state datagram networks distance vector 4.3 what's inside a router hierarchical routing 4.4 IP: Internet protocol 4.6 routing in the Internet datagram format RIP IPv4 addressing OSPF ICMP BGP IPv6 4.7 broadcast and multicast routing Network Layer 4-3
Network Layer 4-3 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 Chapter 4: outline
Network layer s transport segment from sending to receiving host data link 今 on sending side network data link data link data link physica physical encapsulates segments sica into datagrams physical physical go on receiving side to network data link data link delivers segments sical data link transport layer transport network layer protocols data link physical data link data link n every host router data link physical ohysical physical router examines header fields in all ip datagrams passing through it Network Layer 4-4
Network Layer 4-4 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 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
Two key network-layer functions ,o forwarding: move analogy: packets from routers input to appropriate s routing: process of router output planning trip from source to dest .o routing: determine route taken by packets s forwarding:, process from source to dest of getting throug single interchange routing algorithms Network Layer 4-5
Network Layer 4-5 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
Interplay between routing and forwarding routing algorithm routing algorithm determines end-end-path through network local forwarding table forwarding table determines header value output link local forwarding at this router 01003 01012 01112 10011 value in arriving packets header 011 Network Layer 4-6
Network Layer 4-6 1 2 3 0111 value in arriving packet’s header routing algorithm local forwarding table header value output link 0100 0101 0111 1001 3 2 2 1 Interplay between routing and forwarding routing algorithm determines end-end-path through network forwarding table determines local forwarding at this router