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Internet Protocol Fundamentals

Internet Protocol Fundamentals

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Internet Protocol Fundamentals

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  1. Internet Protocol Fundamentals Gateway to the World By Eric L. Michelsen

  2. Topics • Point to Point Links • Subnetting • Classless Inter-Domain Routing (CIDR) • Private Addressing • DNS • UDP • TCP: Reliable Delivery • IPv6 (IP, the Next Generation) • Internet Protocol Services • Where in the Stack Is IP? • IP Addressing • IP Networks and Hosts • IP Network Classes • Multi-homed hosts • Routing • Minimum Host Configuration

  3. Where in the Stack is IP? • IP is a layer 3 protocol (network layer) • IP is designed to run over any and all link layers (layer 2) • IP folk used to think of a 4-layer stack OSI 7 6 5 4 3 2 1 Telnet, FTP, email, Netware services Application Presentation IP 4 3 2 1 Session Application UDP, TCP, Novell SPX Transport Transport TCP, UDP IP, IPX, NetBIOS Network Network IP Ethernet II, IEEE 802.2 Link Physical 10Base-T, T1, V.34, EIA-232 Physical

  4. Internet Protocol Services • IP v4 (RFC-791, and many others) • IP provides 3 primary Services: • Global addressing • Best-effort (not guaranteed) datagram delivery • Fragmentation • Base protocol on which many others are built • Upper layers provide reliability as needed • Fragmentation is inefficient, and generally avoided.

  5. IP Addressing • 32-bit (4-octet) address, written in dotted decimal: w.x.y.z e.g., 206.71.190.4 • w, x, y, and z are octets, ranging from 0 to 255 • Each IP address is globally unique • except for private addresses • An IP network is a group of hosts that can communicate “directly” with each other • “directly” means no intervening IP devices • All IP packets include the destination and source IP address

  6. IP Networks and Hosts • A typical IP network might be an Ethernet: Host 206.71.190.1 Host 206.71.190.2 Host 206.71.190.3 Host 206.71.190.4 206.71.190.0 • Each host interface has an IP address • An IP address includes two parts: the network address, and the host address, e.g. • network 206.71.190 .4 host • All hosts on net have the same network address • The network as a whole is referred to as host = 0

  7. Another Sample IP Network • Full-mesh Frame Relay network • Any two hosts can communicate “directly” • Broadcasts must be duplicated by sender to each VC Host 206.71.190.2 Host 206.71.190.1 PVC Single IP Interface PVC PVC The whole mesh is network 206.71.190.0 PVC PVC PVC Host 206.71.190.3 Host 206.71.190.4 PVC

  8. Classical Class • Network/host address sizes vary in classes: • Class A: N.h.h.h (0.0.0.0 to 127.0.0.0) • 128 networks, 16M hosts per network • Example: 10.1.1.1 network 10, host .1.1.1 • Class B: N.N.h.h (128.0.0.0 to 191.255.0.0) • 16,384 networks, 65k hosts per network • Example: 132.10.5.17 network 132.10, host .5.17 • Class C: N.N.N.h (192.0.0.0 to 223.255.255.0) • 2M networks, 254 hosts per network • Example: 206.71.190.13 network 206.71.190, host .13 • Classes D & E are “special” • Host address of all 1s (e.g., 206.71.190.255) means broadcast to an entire IP network (deprecated)

  9. Multi-homed Host • A host may appear on multiple networks • Each network interface has an IP address 199.107.10.0 199.107.10.12 multi-homed Host 206.71.183.4 206.71.183.0 • A multi-homed host may be used to forward packets between networks (i.e., as a router)

  10. Routing • Connecting networks into an “internetwork” Host Host Host Host 192.168.20.0 192.168.1.0 192.168.1.1 Router 206.71.183.1 192.168.20.1 Router 206.71.183.2 206.71.183.0 Host Host Host Host

  11. forwarded 1st packet 1st packet to 192.168.1.x redirect subsequent packets Minimum Host Configuration • 2 configuration items required for full internetwork access: • An IP address • A default router • Host learns new routes from default router with redirects • Every host (not just routers) must maintain a routing table 192.168.1.0 192.168.20.0 192.168.1.1 Router 206.71.183.1 192.168.20.1 Router 206.71.183.2 IP 206.71.183.9 Default router 206.71.183.2 206.71.183.0 Host

  12. Point-to-Point Links • Numbered Link: standard IP (wasteful) • All hosts must have same network number • Wastes a whole network address for 2 hosts Host 206.71.190.1 Host 206.71.190.2 206.71.190.0 • Unnumbered Link: efficient • No network number • Host addresses are completely arbitrary • Used almost exclusively on routers, and host PPP links Router 206.71.190.3 Router 199.107.183.15 unnumbered

  13. Subnet Masks • The subnet mask defines which parts of an IP address are the ‘network’ and ‘host’ parts • 1s in the subnet mask specify network address bits, 0s specify host address bits • Standard class subnet masks: • Class A: 255.0.0.0 11111111.00000000.00000000.00000000 • Class B: 255.255.0.0 11111111.11111111.00000000.00000000 • Class C: 255.255.255.0 11111111.11111111.11111111.00000000

  14. Subnetting • Creates networks smaller than the default for their class (breaks up Class A, B, & C networks) • Example: subnet mask 255.255.255.192 = 11111111.11111111.11111111.11000000creates a subnet of 64 addresses (62 hosts) • Can use 255.255.255.0 on an (otherwise) Class B network to create 256 Class-C-size subnets (254 hosts) • Network part is always on left end of subnet mask • Handy table: • Sometimes written as /n, where n is # bits in Network part, e.g., /26 => 255.255.255.192 128 1000 0000 240 1111 0000 192 1100 0000 248 1111 1000 224 1110 0000 252 1111 1100

  15. Examples of IP Subnetting • 192.168.1.0/24 (mask 255.255.255.0) • standard Class C • 254 hosts: 192.168.1.1 - 192.168.1.254 • 192.168.2.0/25 (mask 255.255.255.128) • 126 hosts: 192.168.2.1 - 192.168.2.126 • 192.168.2.128/26 (mask 255.255.255.192) • 62 hosts: 192.168.2.129 - 192.168.2.190 • 192.168.2.192/27 (mask 255.255.255.224) • 30 hosts: 192.168.2.193 - 192.168.2.222 192.168.1.0 192.168.1.0/24 192.168.1.255 192.168.2.0 192.168.2.0/25192.168.2.127 192.168.2.128 192.168.2.128/26192.168.2.191 192.168.2.192/27

  16. CIDR • Classless Inter-Domain Routing • Eliminates Class A, B, and C networks. • Subnet masks must be specified for everything • This is a 3rd piece of configuration now required by an IP host: • IP address • Subnet mask • Default Router • Widely used, and growing

  17. Private Addresses • IETF set aside some addresses for “private” use: • 1 Class A network10.0.0.0 • 16 Class B networks172.16.0.0 - 172.31.0.0 • 256 Class C networks192.168.*.0 • Internet routers are configured to discard packets addressed to these addresses • These addresses are not visible to the Internet, so multiple sites can use them at will

  18. DNS: Domain Name System • RFCs 1034, 1035 • Memorizing IP addresses is difficult • DNS is a distributed directory of names, and associated IP addresses, and other info • “First DNS server” is a 4th piece of IP host config • Hierarchical system of shared authority • Right parts are higher authority than left www.enterprise.com Enterprise Administered InterNIC Administered

  19. UDP: User Datagram Protocol • RFC 768 • Built above IP (Layer 4, Transport) • Best-effort, datagram (packet) delivery (connectionless) • Adds an additional addressing layer: port • Each UDP datagram includes a 16-bit destination and 16-bit source port • There are many “well-known” ports, which essentially act as Server IDs or Protocol IDs for UDP • DNS port 53 • BOOTP/DHCP ports 67 (server), 68 (client) • TFTP port 69 • SNMP port 161

  20. TCP: Transmission Control Protocol • RFC 793, plus many modifications • Reliable, error-corrected stream of data • Connection oriented (has setup and teardown) • Uses a highly efficient, self-adjusting pacing mechanism for high throughput • No packetization (or frame) boundaries • Packetization of data stream into IP packets is invisible to the application layer • Packet boundaries (if needed) must be created by higher layers • Like UDP, has ports. Well known ports: • FTP control port 20 • Telnet port 23 • SMTP port 25

  21. IPv6 (IPng) • Primarily intended to address the problem of running out of IP addresses • Aka Network Engineer Employment Act of 1994 • Nearly every IP protocol must change • Nearly every IP software application must change • Addresses extended to 16 octets (128 bits) • Enough for each molecule on the surface of the earth to have its own IP address • Part of address is locally assigned • Fragmentation confined to endpoints (routers don’t fragment, hosts do)

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