Network Layer (OSI and TCP/IP)

1. Network Layer (OSI and TCP/IP) Lecture 9, May 2, 2003 Data Communications and Networks Mr. Greg Vogl Uganda Martyrs University

2. Sources • BITDCO lectures 18-20 • Hodson Ch. 12 • IU A247 lectures 5, 6, 8, 9, 11 • Chappell & Tittel, Guide to TCP/IP, Course Technology, 2002 Data Communications and Networks: Lecture 9: Network Layer

3. Functions of OSI Network Layer • Addressing (sender and receiver machines) • Routing (determining end-to-end path) • Network control (sending/receiving status messages used to make routing decisions) • Congestion control (monitor, reduce delays) Data Communications and Networks: Lecture 9: Network Layer

4. Network Addresses • Domain name e.g. yahoo.com • Human-friendly name of an Internet location • Used in e-mail and web site addresses • IP number e.g. 207.46.230.229 • Logical address of a computer, router, etc. • Set by network administrator • MAC address e.g. 00:00:C0:76:5A:26 • Physical address of a computer NIC Data Communications and Networks: Lecture 9: Network Layer

5. Translating Addresses • Domain Name System (DNS) • Domain name  IP number • Type NSLOOKUP at DOS prompt • Address Resolution Protocol (ARP) • Local IP number  MAC address • Type ARP -A at DOS prompt • Reverse ARP (RARP) • MAC address  local IP number Data Communications and Networks: Lecture 9: Network Layer

6. Routing • If packet destination is not on local subnet • Forward it to default gateway (router or server) • Routing table in memory of each router • Lists links to other network segments/subnets • Goals • Find the most efficient paths; avoid congestion • Convergence: make all routing tables consistent • Avoid routing loops, packets that live forever Data Communications and Networks: Lecture 9: Network Layer

7. Centralised Routing • One node is Network Routing Manager • finds over/under use of connections • calculates optimal paths between nodes • makes, sends routing tables to all nodes • Disadvantages • delays to communicate with NRM • delays receiving tables --> inconsistencies • NRM performance/reliability, need backup Data Communications and Networks: Lecture 9: Network Layer

8. Distributed Routing • e.g. Routing Information Protocol • Each node calculates its own routing table • Periodically transmit status to neighbours • Every 60 seconds, broadcast its routing table • Entries can be added, updated or discarded • Avoids NRM bottleneck • Changes take a long time to reach all nodes Data Communications and Networks: Lecture 9: Network Layer

9. Static vs. Dynamic Routing • Static routing • Always use one particular path • If the path is unavailable use an alternative • Rarely used (connections change; congestion) • Weighted routing • Randomly select a path from weighted alternatives • Dynamic or adaptive routing • Select best current message route using number of hops, speed and type of link, congestion/traffic Data Communications and Networks: Lecture 9: Network Layer

10. Open Shortest Path First (OSPF) • Link state routing • Only store table of directly connected links • Assumes routing tables rarely change • Only send update info when link state changes • Routes based on network bandwidth • Reduced traffic; short convergence time • Now more widely used than RIP • Better for larger (enterprise) networks Data Communications and Networks: Lecture 9: Network Layer

11. Internetworking Protocol Suites • TCP/IP (US Defense Dept, UNIX, etc.) • OSI (ISO) • XNS (Xerox, Ungermann-Bass) • SNA/APPC (IBM) • ATP (Apple) • NetBEUI (Microsoft) • IPX/SPX (Novell) Data Communications and Networks: Lecture 9: Network Layer

12. OSI Model and Real Protocols Data Communications and Networks: Lecture 9: Network Layer

13. TCP/IP Protocols and Layers Data Communications and Networks: Lecture 9: Network Layer

14. OSI Model and Internet Protocols Data Communications and Networks: Lecture 9: Network Layer

15. IP Datagram Delivery • Unreliable delivery • delivery, uniqueness, sequence not guaranteed • reliability handled by higher layer (TCP) • Connectionless Delivery • each packet routed, delivered independently • Best Effort Delivery • drop packets only if no resources (buffer space) Data Communications and Networks: Lecture 9: Network Layer

16. IP Datagram Structure Data Communications and Networks: Lecture 9: Network Layer

17. IP Address Classes Data Communications and Networks: Lecture 9: Network Layer

18. Default Subnet Masks Data Communications and Networks: Lecture 9: Network Layer

19. IP Version 6 (IPv6 or IPng) • IPv4 32-bit addresses are almost all in use • Only 232 (4 billion) unique addresses • Proposed IPv6 uses 128-bit addresses • Many addresses available (2128 = 1038) • Not easily memorised like IPv4 addresses • Displayed in hexadecimal like MAC addresses • Can contain IPv4 and MAC addresses • Some addresses reserved for uni/multi/anycast Data Communications and Networks: Lecture 9: Network Layer

20. Other IP Version 6 features • Registry service with 32 top level registries • Faster routing (addresses, simplified header) • Quality of Service (reserve resources, request high performance for voice/video) • Security (authentication/encryption) • Auto-configuration (automatically choose an address; similar to BOOTP/DHCP) • Mobile uses (cellphone/wireless) Data Communications and Networks: Lecture 9: Network Layer