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Topic 6: Network Layer- Chapter 5 : The Internet: Addressing & Services

Business Data Communications, 4e

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Internet Addressing

32-bit global internet address Includes network and host

identifiersDotted decimal notation

11000000 11100100 00010001 00111001 (binary)

192.228.17.57 (decimal)

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Types of addresses

Address Example Software Example Address

Application Layer Web browser ike.ba.ttu.eduNetwork Layer TCP/IP 129.118.49.189Data Link Layer Ethernet 00-A0-C9-96-1D-90

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Addressing

The network layer determines the best route through the network to the final destination.

Based on this routing, the network layer identifies the data link layer address of the next computer to which the message should be sent.

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Assigning Addresses

In general, the data link layer address is permanently encoded in each network card, and as part of the hardware that cannot be changed.

Network layer addresses are generally assigned by software. Every network layer software package usually has a configuration file that specifies the network layer address for that computer.

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Assigning Addresses

Application layer addresses (or server addresses) are also assigned by a software configuration file. Virtually all servers have an application layer address, but most client computers do not.

Network layer addresses and application layer addresses go hand in hand. (ruby.bus.utexas.edu - means 146.6.44.95 at the network layer.)

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*How IP Addresses Distributed Internet Corporation for Assigned Names and

Numbers (ICANN) oversees the Internet Assigned Numbers Authority (IANA) and controls how the Net's 4.29 billion IP addresses are used.

IANA distributes address space to three geographically diverse Regional Internet Registries (RIRs) and encourage three RIRs to operate so that addresses remain unique, are mapped efficiently, and are treated as a precious resource.

Three RIRs dole out available pools of IP based on a shared criteria. All deploy numerical address space to ISPs, local registries, and in some cases small users.

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IP Address AllocationIANAIANA

InterNICInterNICAmericaAmerica

RIPERIPEEuropeEurope

APNICAPNICAsiaAsia

NationalNational

RegionalRegional

ConsumerConsumer

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American Registry for Internet Numbers (ARIN) Reseaux IP Europeen (RIPE) Asia Pacific Network Information Centre

(APNIC)

Three RIRs

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Internet AddressesInterNIC is responsible for network layer

addresses (IP addresses) and application layer addresses or domain names (www.ttu.edu).

There are five classes of Internet addresses.Classes A, B, and C are available to

organizationsClass D and E are reserved for special

purposes and are not assigned to organizations.

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Internet Address Classes Class A (/8 address)

The first digit is fixed, ranging 1-126 (01-7E), 16 million addresses

127.x.x.x is reserved for loopback Class B (/16 address)

First two bytes are fixed with the first digit ranging 128-191 (80-BF), 65,000 addresses.

Class C (/24 address) First 3 bytes are fixed, with the first digit ranging 192-223

(C0-DF), 254 addresses. Class D & E

The first digit is 224-239 (E0-EF) and 240-255 (F0-FF) respectively.

Reserved for special purposes and not available to organizations.

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Internet Address Classes

1/2

1 126

1/4

128 191

1/8

192 223

1/16 1/16

240 255

Class C Class D Class EClass BClass A

Ranges of the first byte for different classes:

Class A: 0xxxxxxxClass B: 10xxxxxx.xxxxxxxxClass C: 110xxxxx.xxxxxxxx.xxxxxxxxClass D: 1110xxxx.xxxxxxxx.xxxxxxxxClass E: 1111xxxx.xxxxxxxx.xxxxxxxx

224 239

Note:The IP addresses with the first byte as 0 and 127 are reserved

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Internet Address Classes # of Addresses

Class Available Addr-Structure Example Available #

Class A 16 million First byte fixed 50.x.x.x126

Organization assigns last three bytes

Class B 65k First two bytes fixed 128.192.x.x 16kOrganization assigns last two bytes

Class C 254 First three bytes fixed 192.1.56.x 2 millionsOrganization assignslast byte

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Internet Addresses

The Internet is quickly running out of addresses. Although there are more than 1 billion possible addresses, the fact that they are assigned in sets (or groups) significantly restricts the number of usable addresses.

The IP address shortage was one of the reasons behind the IPv6, providing in theory, 3.2 x 1038 possible addresses.

How to apply for IP address?

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SubnetsAssign IP addresses to specific computers so that all

computers on the same local area network have a similar address.

Each LAN that is logically grouped together by IP number is called a TCP/IP subnet.

Benefit: allows it to be connected to the Internet with a

single shared network address an necessary use of the limited number of

network numbers Overload Internet routing tables on gateways

outside the organization

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Gateway

128.192.254.2

146.7.11.1

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Subnet Mask

Subnet mask enables a computer to determine which computers are on the same subnet. This is very important for message routing.

E.g. IP address: 129.118.49.189Subnet mask: 255.255.255.0 IP address: 129.118.49.x is for the

computers in the same subnet

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Subnet

Subnet with partial bytes addresses.

E.g. 129.118.49.1 to 129.118.49.126

Subnet mask: 255.255.255.128Subnet address: 129.118.49.0Subnet broadcast address:

129.118.49.127

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Subnet

IP address:129.118.49.111 1000 0001.0111 0110.0011 0001.0110 1111Subnet mask:255.255.192.0 1111 1111.1111 1111.1100 0000.0000 0000The IP prefix 1000 0001.0111 0110.00

Destination IP:129.118.51.254 1000 0001.0111 0110.0011 0011.0110 1111

Destination IP:128.83.127.1 1000 0000.0101 0011.0111 1111.0000 0001

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Subnet Mask Template150.1.0.0150.1.0.0

1 0 0 1 0 1 1 01 0 0 1 0 1 1 0

150150

0 0 0 0 0 0 0 10 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

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00 00

Network ID–Class BNetwork ID–Class B

Host AddressHost Address

Possible Subnet AddressPossible Subnet Address

128128192192

224224240240

248248252252

254254255255

128128192192

224224240240

248248252252

255255 255255

Broadcast AddressBroadcast Address

128 64 32 16 8 4 2 1128 64 32 16 8 4 2 1

Mask NumbersMask Numbers

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Dynamic Addressing

An address assignment problem: Each time the computer is moved, or its network is assigned a new address, the software on each individual computer must be updated.

Solution: dynamic addressing With this approach, a server is designated to supply a network layer address to a computer each time the computer connects to the network.

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Dynamic Addressing

Two standards for dynamic addressing are commonly used in TCP/IP networks: Bootstrap Protocol (bootp) for

dial-up networks (1985) Dynamic Host Control Protocol

(DHCP) for non-dial-up networks (1993)

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Dynamic Addressing

The Bootp or DHCP server can be configured to assign the same network layer address to the computer each time it requests an address or it can lease the address to the computer by picking the “next available” network layer address from a list of authorized addresses.

Dynamic addressing greatly simplifies network management in non-dial-up networks too.

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Address Resolution

Address resolution:The sender translates the application layer address (or server name) of the destination into a network layer address; and in turn translates that into a data link layer address.

Two approaches used in TCP/IP: Server address resolution Data link layer address resolution.

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Domain

A domain refers to a group of networks that are under the administrative control of a single entity, such as a company.

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Server Name Resolution

Domain Name Service (DNS)Used for translating application layer addresses into network layer addresses.

InterNICKeeps the name and IP addresses of the name server that will provide DNS information for your address classes.

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Domain Name System

32-bit IP addresses have two drawbacks Routers can’t keep track of every network path Users can’t remember dotted decimals easily

Domain names address these problems by providing a name for each network domain (hosts under the control of a given entity)

See Figure 5.6 for example of a domain name tree

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DNS Database

Hierarchical database containing name, IP address, and related information for hosts

Provides name-to-address directory services

Key features: Variable-depth hierarchy. Unlimited levels Distributed database. Scattered throughout the

Internet and private intranet. Distribution controlled by the database.

Thousands of separately managed zones managed by separate administrators

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Server Name Resolution

Server address resolution process: TCP/IP sends a special TCP-level packet to the nearest DNS

server asking for the requesting computer the IP address that matches the Internet address provided.

If the DNS does not have the answer for the request, it will forward the request to another DNS.

This is why it sometimes takes a long time to access certain sites.

IP addresses are then temporarily stored in a server address table.

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Data Link Layer Address Resolution

In order to actually send a message, the network layer software must know the data link layer of the destination computer.

In the case of a distant computer, the

network layer would route the message by selecting a path through the network that would ultimately lead to the destination.

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Data Link Layer Address Resolution

The process: TCP/IP software sends a broadcast message

(using Address-Resolution-Protocol or ARP) to all computers in its subnet requesting the data link layer address.

The computer with the right IP address responds with its data link layer address

The message is sent to the destination computer

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RoutingThere are many possible routes or paths a

message can take to get from one computer to another.

RoutingThe process of determining the route or path through the network that a message will travel from the sender to the receiver.

Routing tableThe routing information on each router, which specifies how message will travel through the network.

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Dynamic Routing

There are three commonly used dynamic routing protocols Routing Information Protocol (RIP) - used by

the network manager to develop the routing table. Used by both TCP/IP and IPX/SPX.

Internet Control Message Protocol (ICMP) - used on the internet with TCP/IP.

Open Shortest Path First (OSPF) uses the number of computers in a route as well as network traffic and error rates to select the best route.

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Connectionless vs. Connection-Oriented Routing

Two ways a group of packets can be routed: Connectionless routing

Each packet is treated separately and makes its own way through the network.

Connection-Oriented routing Sets up a virtual circuit between the sender and

receiver. Appears to use point-to-point circuit-switching, but actually uses store-and-forward.

Has greater overhead than connectionless, due to the routing information.

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Connectionless vs. Connection-Oriented

Virtual CircuitAppears to the application

software to use a point-to-point circuit

The network layer makes one routing decision and all packets follow the same route

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Connectionless vs. Connection-Oriented

TCP vs. UPD TCP is used for connection-oriented

routing TCP establishes the virtual circuit and IP

routes the messages. UDP is used for connectionless routing

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Multicast

UnicastingThe usual transmission between two computers.

Broadcasting Sending messages to all computers on a LAN or subnet.

MulticastingSending the same message to a group of computers temporarily in a class D IP address. IGMP is used for multicast.

AnycastingAn IPv6 transmission method allowing messages to be sent to any one of the host in a sub-network.

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Quality of Service

Quality of Service (QoS): The idea that transmission quality (rates,

error rates, bandwidth and jitter) can be measured, improved, and, to some extent, guaranteed in advance.

QoS routing: A special type of connection-oriented

dynamic routing in which different messages or packets are assigned different priorities.

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Categories of Traffic

Elastic traffic, such as FTP, email, etc Allow fluctuating bandwidth, the total

transmission time is important The data must correctly transmitted

Real-time traffic, such as videoconferencing. Demands certain bandwidth with isochronous

features Tolerates some level of errors. Service quality includes: Throughput, Delay,

Delay variation, and Packet loss.

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Routing at Routers Bandwidth schedule

First in first out Round robin Prioritization

Queue management Packet discard policy Congestion control

Packet Drop

Packet arrival Packet forward

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Network Congestion

What is traffic congestion? The buffer in a forwarding device

overflows. This results packet losses and incur retransmission. The transmission will worsen the situation.

Network congestion control is very important in flow management

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Internet Flow Control

Internet flow control algorithm Slow start, congestion avoidance

Router queue management Random early detection (RED) for packet

dropping

Data flow scheduling FIFO, round robin, priority queueing,

weighted fair queueing

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Internet Flow Control

Slow Start algorithm (RFC2001). To avoid router running out of space

Two windows: advertised window by receiver and congestion window by sender. The congestion window is flow control imposed by the sender, while the advertised window is flow control imposed by the receiver.

The congestion window is initialized to one segment. Each time an ACK is received, the congestion window is increased by one segment. The sender can transmit up to the minimum of the congestion window and the advertised window.

The sender starts by transmitting one segment and waiting for its ACK. When that ACK is received, the congestion window is incremented from one to two, and two segments can be sent.

When each of those two segments is acknowledged, the congestion window is increased to four. This provides an exponential growth.

At some point the capacity of the internet can be reached, and an intermediate router will start discarding packets. This tells the sender that its congestion window has gotten too large.

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Internet Flow Control

Congestion Avoidance (RFC2001) Sets congestion window to one segment. When congestion occurs (indicated by a timeout or the reception of

duplicate ACKs), one-half of the current window size (the minimum of congestion window and the receiver's advertised window, but at least two segments) is saved as X.

When new data is acknowledged by the other end, increase congestion window, but the way it increases depends on whether TCP is performing slow start or congestion avoidance. If congestion window is less than or equal to X, TCP is in slow start; otherwise TCP is performing congestion avoidance.

Slow start continues until TCP is halfway to where it was when congestion occurred (since it recorded half of the window size that caused the problem in step 2), and then congestion avoidance takes over.

Congestion avoidance dictates that congestion window be incremented a linear growth of congestion window, compared to slow start's exponential growth.

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Internet transmission services

Best-effort services The Internet treats all packet equally.

Integrated services (IntServ) IntServ refers to mechanisms that enable

users to request a particular QoS for a flow of data.

Differentiated Services (DiffServ) DiffServ Use type-of-service in IPv4 header

to indicate the required service quality.

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Integrated Services

Routers require additional functionality to handle QoS-based service

IETF is developing suite of standards to support this

Two standards have received widespread support Integrated Services Architecture (ISA): To

enable the provision of QoS support over IP-based Internet.

Resource ReSerVation Protocol (RSVP)

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Integrated Services Architecture

Enables provision of QoS over IP-networks

Features include Admission Control: A new flow needs a

reservation for QoS Routing Algorithm: more parameters are

considered other than just delay Queuing Discipline: Queuing policy takes

into account of different requirements Discard Policy: Particularly for congestion

management

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Resource Reservation Protocol (RSVP)

A tool for prevention of congestion through reservation of network resources

Can be used in unicast or multicast transmissions Receivers (not senders) initiate resource reservations Operation:

Complexity is in multicast transmission RSVP uses two basic messages: Resv and Path. In multicast,

Resv messages generated by one of the multicast group receivers propagate upstream through distribution tree and create soft state in routers. Once it reaches the sender, hosts are enabled to set parameters for the first hop. Path is used to provide upstream routing information and sent from senders via the down stream tree to all receivers

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Differentiated Services (DiffServ)

Provides QoS based on user group needs rather than traffic flows

Can use current IPv4 octetsService-Level Agreements (SLA)

govern DiffServ, eliminating need for application-based assignment

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IPv4 Type of Service Field

Allows user to provide guidance on individual datagrams

3-bit precedence subfield Indicates degree of urgency or priority Queue Service & Congestion Control

4-bit TOS subfield Provides guidance on selecting next hop Route selection, Network Service, & Queuing

Discipline

Precedence TOS 0

0 1 2 3 4 5 6 7

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DiffServ Domains

Host

Host

Interior component

Border component

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DiffServ Operation

Routers are either boundary nodes or interior nodes

Interior nodes use per-hop behavior (PHB) rules

Boundary nodes have PHB & traffic conditioning

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Token Bucket SchemeMax Burstiness:

RT + B

R: Token replenishment rateB: Bucket size

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TCP/IP Configuration Information

At least four pieces of information needed for a client computer TCP/IP configuration IP address Subnet mask Gateway IP address Domain name Server IP address

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*Some Network Commands

Some useful network commands ping finger nslookup tracert ipconfig

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Port Addresses

What is a port address? A unique number assigned to a network

application as an address to receive or send data.

Why need port addresses? A single host may run several servers, such as

Web, FTP, Telnet, Email, etc. When the network layer receives a message, it needs to know which application layer software package should receive the message.

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Application Layer Port Addresses

Port numbers are divided in three ranges: Well-known ports: 0-1023, controlled

by IANA Registered ports: 1024-49151 Dynamic or private ports: 49152-

65535. We also call them ephemeral ports.

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Application Layer Port Addresses

Default port number assignments Web: 80 (or 8080) FTP: 21 News group: 119 (or 8119) Telnet: 23 SMTP: 25

IANA (Internet Assigned Numbers Authority) is taking care this issue.

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*WINS WINS (Windows Internet Naming Service) manages the

association of workstation names and locations with IP addresses without the user or an administrator having to be involved in each configuration change.

WINS automatically creates a computer name-IP address mapping entry in a table. When a computer is moved to another geographic location, the new subnet information will be updated automatically in the WINS table.

WINS complements the NT Server's DHCP. WINS have been submitted to IETF as proposed open

standards. New features are included in the follow-on to Windows NT, Windows 2000.

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*News about IPv6

"IPv6 Internet Protocol Comes of Age“, AsiaBizTech (07/16/01) IP version 6 (IPv6) will be unrolled in three waves extending from mid-2001 through 2003:

The arrival of home gateways and IPv6-compliant PCs will comprise the first phase;

the second wave will be marked by the advent of networked household appliances;

the third wave will be the release of IPv6-enabled mobile phones.

ISPs and manufacturers of equipment such as routers and switches expect to benefit by accelerating their own IPv6 development initiatives. The first wave is expected to hit at the same time Microsoft introduces Windows XP in October of this year, thus changing over its PC line to IPv6. The first manifestations of the second wave will be home gateways and IPv6-enabled game consoles, followed by AV gear such as DVD players and camera-equipped VCRs. NTT DoCoMo and the J-Phone Group are among the cellular carriers readying IPv6-capable products in preparation for the third wave in early 2003.