Inductive Logic

Internet Protocol FundamentalsInternet Protocol Fundamentals

Gateway to the World

By Eric L. Michelsen

11/9/2000 2Inductive Logic

TopicsTopics 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

Point to Point Links Subnetting Classless Inter-Domain

Routing (CIDR) Private Addressing DNS UDP TCP: Reliable Delivery IPv6 (IP, the Next

Generation)

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Where in the Stack is IP?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

7

6

5

4

3

2

1 Physical

Link

Network

Transport

Session

Presentation

Application

10Base-T, T1, V.34, EIA-232

Ethernet II, IEEE 802.2

IP, IPX, NetBIOS

UDP, TCP, Novell SPX

Telnet, FTP, email, Netware services

OSI

Physical

Application

Network

Transport

IP

4

3

2

1

IP

TCP, UDP

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Internet Protocol ServicesInternet 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.

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IP AddressingIP 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

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IP Networks and HostsIP Networks and Hosts A typical IP network might be an Ethernet:

Host206.71.190.4

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

206.71.190.0

Host206.71.190.3

Host206.71.190.2

Host206.71.190.1

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Another Sample IP NetworkAnother Sample IP Network

Full-mesh Frame Relay network• Any two hosts can communicate “directly”

Broadcasts must be duplicated by sender to each VC

The whole mesh is network 206.71.190.0

Host206.71.190.4

Host206.71.190.3

Host206.71.190.2

Host206.71.190.1

PVC

PVC

PVC PVCPVC

PVC

Single IP Interface

PVC

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Classical ClassClassical 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)

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Multi-homed HostMulti-homed Host

A host may appear on multiple networks Each network interface has an IP address

199.107.10.12

multi-homed Host

206.71.183.4

206.71.183.0

199.107.10.0

A multi-homed host may be used to forward packets between networks (i.e., as a router)

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RoutingRouting

Connecting networks into an “internetwork”

Host

192.168.1.1 Router

206.71.183.1

206.71.183.0

192.168.20.1 Router

206.71.183.2

192.168.20.0192.168.1.0

HostHostHost

HostHostHostHost

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Minimum Host ConfigurationMinimum 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

192.168.1.1 Router

206.71.183.1

206.71.183.0

192.168.20.1 Router

206.71.183.2

Host

IP 206.71.183.9Default router 206.71.183.2

1st packet to 192.168.1.x

redirect

forwarded 1st packet

subsequent packets

192.168.20.0192.168.1.0

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Point-to-Point LinksPoint-to-Point Links Numbered Link: standard IP (wasteful)

• All hosts must have same network number• Wastes a whole network address for 2 hosts

Unnumbered Link: efficient• No network number• Host addresses are completely arbitrary• Used almost exclusively on routers, and host PPP links

Host206.71.190.2

206.71.190.0Host206.71.190.1

Router199.107.183.15

unnumberedRouter206.71.190.3

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Subnet MasksSubnet 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

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SubnettingSubnetting 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 1000224 1110 0000 252 1111 1100

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Examples of IP SubnettingExamples 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

192.168.2.128 192.168.2.128/26192.168.2.191

192.168.1.0

192.168.1.0/24

192.168.1.255

192.168.2.192/27

192.168.2.0

192.168.2.0/25

192.168.2.127

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CIDRCIDR

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

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Private AddressesPrivate Addresses

IETF set aside some addresses for “private” use:• 1 Class A network 10.0.0.0• 16 Class B networks 172.16.0.0 - 172.31.0.0• 256 Class C networks 192.168.*.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

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DNS: Domain Name SystemDNS: 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

InterNICAdministered

EnterpriseAdministered

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UDP: User Datagram ProtocolUDP: 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

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TCP: Transmission Control ProtocolTCP: 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

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IPv6 (IPng)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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