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Network Layer (OSI and TCP/IP) Lecture 9, May 2, 2003 Data Communications and Networks Mr. Greg Vogl Uganda Martyrs University 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 May 2, 2003 Data Communications and Networks: Lecture 9: Network Layer 2 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) May 2, 2003 Data Communications and Networks: Lecture 9: Network Layer 3 Network Addresses Domain name e.g. yahoo.com – – IP number e.g. 207.46.230.229 – – Human-friendly name of an Internet location Used in e-mail and web site addresses Logical address of a computer, router, etc. Set by network administrator MAC address e.g. 00:00:C0:76:5A:26 – May 2, 2003 Physical address of a computer NIC Data Communications and Networks: Lecture 9: Network Layer 4 Translating Addresses Domain Name System (DNS) – – Address Resolution Protocol (ARP) – – Domain name IP number Type NSLOOKUP at DOS prompt Local IP number MAC address Type ARP -A at DOS prompt Reverse ARP (RARP) – May 2, 2003 MAC address local IP number Data Communications and Networks: Lecture 9: Network Layer 5 Routing If packet destination is not on local subnet – Routing table in memory of each router – Forward it to default gateway (router or server) Lists links to other network segments/subnets Goals – – – May 2, 2003 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 6 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 – – – May 2, 2003 delays to communicate with NRM delays receiving tables --> inconsistencies NRM performance/reliability, need backup Data Communications and Networks: Lecture 9: Network Layer 7 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 May 2, 2003 Data Communications and Networks: Lecture 9: Network Layer 8 Static vs. Dynamic Routing Static routing – – – Weighted routing – Always use one particular path If the path is unavailable use an alternative Rarely used (connections change; congestion) Randomly select a path from weighted alternatives Dynamic or adaptive routing – May 2, 2003 Select best current message route using number of hops, speed and type of link, congestion/traffic Data Communications and Networks: Lecture 9: Network Layer 9 Open Shortest Path First (OSPF) Link state routing – Assumes routing tables rarely change – Only send update info when link state changes Routes based on network bandwidth – Only store table of directly connected links Reduced traffic; short convergence time Now more widely used than RIP – May 2, 2003 Better for larger (enterprise) networks Data Communications and Networks: Lecture 9: Network Layer 10 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) May 2, 2003 Data Communications and Networks: Lecture 9: Network Layer 11 OSI Model and Real Protocols May 2, 2003 Data Communications and Networks: Lecture 9: Network Layer 12 TCP/IP Protocols and Layers May 2, 2003 Data Communications and Networks: Lecture 9: Network Layer 13 OSI Model and Internet Protocols May 2, 2003 Data Communications and Networks: Lecture 9: Network Layer 14 IP Datagram Delivery Unreliable delivery – – Connectionless Delivery – delivery, uniqueness, sequence not guaranteed reliability handled by higher layer (TCP) each packet routed, delivered independently Best Effort Delivery – May 2, 2003 drop packets only if no resources (buffer space) Data Communications and Networks: Lecture 9: Network Layer 15 IP Datagram Structure May 2, 2003 Data Communications and Networks: Lecture 9: Network Layer 16 IP Address Classes May 2, 2003 Data Communications and Networks: Lecture 9: Network Layer 17 Default Subnet Masks May 2, 2003 Data Communications and Networks: Lecture 9: Network Layer 18 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 – – – – – May 2, 2003 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 19 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) May 2, 2003 Data Communications and Networks: Lecture 9: Network Layer 20