Graciela Perera Department of Computer Science and Information Systems Slide 1 of 18 INTRODUCTION NETWORKING CONCEPTS AND ADMINISTRATION CSIS 3723 Graciela Perera Department of Computer Science and Information Systems Meshel Hall 320 (330)

Graciela Perera Department of Computer Science and Information Systems Slide 2 of 18 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) –dealing with scale –advanced topics: IPv6, mobility instantiation, implementation in the Internet

Graciela Perera Department of Computer Science and Information Systems Slide 3 of 18 Chapter 4: Network Layer Introduction Routing algorithms –Link state –Distance Vector Virtual circuit and datagram networks What’s inside a router IP: Internet Protocol –Datagram format –IPv4 addressing –ICMP –IPv6 Routing in the Internet –RIP –OSPF –BGP

Graciela Perera Department of Computer Science and Information Systems Slide 4 of 18 Router Architecture Overview Two key router functions: run routing algorithms/protocol (RIP, OSPF, BGP) forwarding pkts from incoming to outgoing link

Graciela Perera Department of Computer Science and Information Systems Slide 5 of 18 Input Port Functions Decentralized switching: given datagram dest., lookup output port using forwarding table in input port memory goal: complete input port processing at ‘line speed’ queuing: if datagrams arrive faster than forwarding rate into switch fabric Physical layer: bit-level reception Data link layer: e.g., Ethernet see chapter 5

Graciela Perera Department of Computer Science and Information Systems Slide 6 of 18 Three types of switching fabrics

Graciela Perera Department of Computer Science and Information Systems Slide 7 of 18 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 Output Port Memory System Bus

Graciela Perera Department of Computer Science and Information Systems Slide 8 of 18 Switching Via a Bus Pkt 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

Graciela Perera Department of Computer Science and Information Systems Slide 9 of 18 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 60 Gbps through the interconnection network

Graciela Perera Department of Computer Science and Information Systems Slide 10 of 18 Output Ports Buffering required when datagrams arrive from fabric faster than the transmission rate Scheduling discipline chooses among queued datagrams for transmission

Graciela Perera Department of Computer Science and Information Systems Slide 11 of 18 Output port queueing buffering when arrival rate via switch exceeds output line speed queueing (delay) and loss due to output port buffer overflow!

Graciela Perera Department of Computer Science and Information Systems Slide 12 of 18 Input Port Queuing Fabric slower than 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!

Graciela Perera Department of Computer Science and Information Systems Slide 13 of 18 Chapter 4: Network Layer Introduction Virtual circuit and datagram networks What’s inside a router Routing algorithms –Link state –Distance Vector IP: Internet Protocol –Datagram format –IPv4 addressing –ICMP –IPv6 Routing in the Internet –RIP –OSPF –BGP

Graciela Perera Department of Computer Science and Information Systems Slide 14 of 18 The Internet Network layer forwarding table Host, router network layer functions: Routing protocols path selection RIP, OSPF, BGP IP protocol addressing conventions datagram format packet handling conventions ICMP protocol error reporting router “signaling” Transport layer: TCP, UDP Link layer physical layer Network layer

Graciela Perera Department of Computer Science and Information Systems Slide 15 of 18 Chapter 4: Network Layer Introduction Virtual circuit and datagram networks What’s inside a router IP: Internet Protocol –Datagram format –IPv4 addressing –ICMP –IPv6 Routing algorithms –Link state –Distance Vector –Hierarchical routing Routing in the Internet –RIP –OSPF –BGP Broadcast and multicast routing

Graciela Perera Department of Computer Science and Information Systems Slide 16 of 18 IP datagram format ver length 32 bits data (variable length, typically a TCP or UDP segment) 16-bit identifier header checksum time to live 32 bit source IP address IP protocol version number header length (bytes) max number remaining hops (decremented at each router) for fragmentation/ reassembly total datagram length (bytes) upper layer protocol to deliver payload to head. len type of service “type” of data flgs fragment offset upper layer 32 bit destination IP address Options (if any) E.g. timestamp, record route taken, specify list of routers to visit. how much overhead with TCP? r 20 bytes of TCP r 20 bytes of IP r = 40 bytes + app layer overhead

Graciela Perera Department of Computer Science and Information Systems Slide 17 of 18 IP Fragmentation & 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 fragmentation: in: one large datagram out: 3 smaller datagrams reassembly

Graciela Perera Department of Computer Science and Information Systems Slide 18 of 18 Chapter 4: summary Introduction Routing algorithms –Link state –Distance Vector Virtual circuit and datagram networks What’s inside a router IP: Internet Protocol –Datagram format –IPv4 addressing –ICMP –IPv6 Routing in the Internet –RIP –OSPF –BGP