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CHAPTER ELEVEN

INTERNET PROTOCOLS AND

APPLICATIONS

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In this chapter we discuss THE INTERNET

there can be many internets, but there is only one Internet

We will be talking about TCP/IP

•Internet Protocol IP

•Transmission Control Protocol TCP

Originally developed by the Department of Defense

DARPA, ARPANET

We currently run IPv4 but are in the process of switching to IPv6

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Overview of TCP/IP

TCP Transmission Control ProtocolIP Internet Protocol

TCP provides connection oriented services for layer 5 of theprotocol stack and relies on IP to route packets throughthe network

Two ends that implement TCP execute a handshake that establishesa logical connection between them. Each side then executes flowcontrol protcols, acknowledge segments, and responds to thosethat arrive damaged.

UDP (User Datagram Protocol) is an alternative layer 4 protocol.

Connectionless, no flow control, no guaranteed delivery.less overhead.

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Some of the protocols supported by TCP/IP

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The Internet Protocol is a layer 3 protocol designed to providea packet delivery service between two sites.

It is commonly but not exclusively used with TCP

Suppose two applications, A and B, need a connection-orientedservice. TCP provides the reliable connection and IP handles routingthrough the different networks.

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Internet Addressing

to users, an internet address has the form:

server.institution.domain

This might appear in your email address as:

user@server.institution.domain

for browsers, the term www represents the default server at the specified location.

periods are used to separate the terms.

In this context, domain does not have the same meaning as that usedin prior chapters.

A DOMAIN is a collection of sites of a particular type. They haveno geographic significance.Table 11.1 contains a list of domain names, some of which are new andmay not be familiar to youl

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When the site is small and a default server is used, the server namecan be omitted.

We can have more components in this text address:

example:www.legis.state.wi.us

In this case, top domain is country us in this exampleit is divided into two subdomains:

wi for Wisconsin

the wi subdomain is further divided into “state” to indicatestate offices

the remaining components indicate the legislative branch and thedefault web server.

These addresses are translated into actual internet addresses

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Current IPv4 Internet Addresses:

Use dotted decimal notation.

Actual address in a 32 value divided into 4 eight bit fields

the address on the previous slide actually has an address of:

143.200.128.162

The maximum value in any of these fields is 255 which is the largestunsigned integer that can be represented with 8 bits.

IP has several classes of internet addresses.

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Class A: 128 possible networks, with up to 16,777,216 nodes

0nnnnnnn xxxxxxxx xxxxxxxx xxxxxxxx

Class B: 16,384 possible networks with up to 65,536 nodes

10nnnnnn nnnnnnnn xxxxxxxx xxxxxxxx

Class C: 2,097,152 possible networks, with up to 256 nodes

110nnnnn nnnnnnnn nnnnnnnn xxxxxxxx

Class D addresses used for multicasting1110 followed by a 28 bit multicast address

Class E reserved

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Classless Addresses:

IPv4 is beginning to encounter problems. With 32 bits addresses,we could have over 4.3 billion unique addresses, but the classaddress system is inefficient, many addresses are wasted and weare starting to run out.

Using the smaller class C addresses increases the number of networkaddresses that routers must deal with, thereby complicatingthe routing problem.

One solution to the problem is a new addressing scheme:

IPv6 uses 128 bit addresses.

Another approach is to use classless addressing.

Called the classless interdomain routing or CIDR, it is currentlysupported by BGP-4 (border gateway protocol version 4)

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How does CIDR work?

It specifies a group of addresses that do not fall into any of thepredefined classes, yet each address in the group can still beinterpreted as a network number followed by a local identifier.

The number of bits defining the network number varies toallow networks of varying size.

It is commonly used to allocate multiple class C networks.Example:suppose and organization the need of up to 1000 stations.

The CIDR approach would be to allocate four consecutiveclass C networks.

Consider the following addresses:

CSC 311Class C Networks Bit Representation Address Range211.195.8.0 11010011-11000011-00001000-xxxxxxxx 211.195.8.0 to 211.195.8.255

211.195.9.0 11010011-11000011-00001001-xxxxxxxx 211.195.9.0 to 211.195.9.255

211.195.10.0 11010011-11000011-00001010-xxxxxxxx 211,195.10.0 to 211.195.10.255

211.195.11.0 11010011-11000011-00001011-xxxxxxxx 211.195.11.0 to 211.195.11.255

In general, these Class C networks correspond to the contiguous set of addresses from 211.195.8.0 to 211.195.11.255

If you examine the addresses carefully, you will note that the first 22 bits of allfour addresses are the same. So we can view any of these Class C networks asa 22 bit network address followed by a 10 bit local identifier.

Furthermore, a router could extract the network number (in this case 211.195.8.0)via a logical AND between the 22 bit subnet mask and an IP address

If we used 8 Class C addresses the first 21 bits would be the same an you couldhave 2K nodesFor 16 Class C addresses the first 20 bits would be the same and you could have4K nodes.

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How do routers extract the network address?

The first three bits determine whether it is a Class A, B, or C address

but what can be done when the number of bits in the network number

varies, as it does with CIDR

The router must know the number of bits in the network ID.

Consequently, the usual representation of a network address,

w.x.y.z is replaced by w.x.y.z./m, where m represents the number

of bits in the network ID.

For example, a router can represent the four networks above usingthe single entry: 211.195.8.0/22, the 22 indicates the network numberis 22 bits long.

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There are international organizations that assign internet addresses

and others that register domain names for a fee.

These domains and IP addresses are kept in a distributed database,

host computer calls on one of these databases to translate the text

domain name into an internet address.

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Zones in a DNS hierarchy

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An IP Packet

Version: version of IP that created the packetHeader Length: number of 32 bit words in the packet headerType of Service: packet handling requests. More recently QofS issues addressed by complex

protocols.Packet Length: length of entire packetIdentification, Flags, Fragment Offset: used in fragmentationTime to Live: max. time for packet to remain on the Internet.Protocol: Specifies higher layer protocol using IPChecksum: Used for error detection on the packet headersSource and Destination IP address.Options: Used to request special treatment.

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Fragmentation:

In transferring a packet across the Internet, many different

network architectures may be encountered. These may require

different packet sizes.

In such instances, it may become necessary to break a packet

into smaller packets.

This process is called fragmentation.

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The packet’s identification value is placed into each packet’ Identification field.The flag field contains a more fragments bit mfbEach fragment will have an offset field to indicate where it goes in the reassembledpacket.

It measure offsets in units of 8 bytes.

CSC 311IP Routing

Relies heavily on RIP-2 and BGP protocols previously discussed.

To get to the actual device on a LAN, we need a physical address

rather than an IP address

Answer: The router keeps tables correlating IP addresses of devices

on its network to their physical addresses.

The router, if it does not have this address, can obtain it by broadcastingthe IP address on the network, the device which has that IP addresswill respond with its physical address. Obviously, we do not want to have to perform such broadcasts for every packet received, so the Routerkeeps a record of these responses.

What happens if a network card in one of the machines needs to be replaced? The entries in the router database are purged periodically, sonew network cards would be detected fairly quickly. Much like the processwe discuss with bridge routing tables.

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Routers:

functions:•extract the destination address from the packet

•find that address in the routing table

•access the next hop value and determine the proper outgoing port

•move the packet to a waiting queue for that port

•transmit the packet

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put in other stuff next time

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IPv6

As previously stated, IPv4 is showing signs of age.Many things in the field of telecommunications have changedsince its inception.

We are running out of addresses.

mobile computing

personal communication devices

Streaming video requires attention to Quality of Service issues, etc.

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IPv6 Packet Header format:

There are fewer options in the header and the address fieldshave been expanded to 128 bits.

The next header field allows insertion of an additional headerbetween the standard header and the payload to provide informationabout options.At present, there are 6 types of extension headers.

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IPv6 Addressing:

Obviously, 128 bit addresses provide for substantially more addressesthan IPv4.

With IPv4 we had about 4.3 billion possible addresses.

With IPv6 we have 2128 possible addresses, an almostunimaginably large number.

In fact, if IPv6 possible addresses were spread out evenly over thesurface of the earth, there would be 1024 addresses for eachsquare meter of the earth’s surface, many more than the total numberof IPv4 addresses currently available. It is inconceivable that thissupply of addresses could ever be exhausted.

Whereas IPv4 uses dotted decimal notation, IPv6 uses Hex/colonnotation

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For example:

7477:0000:0000:0000:0000:0AFF:1BDF:7FFFF

would be a valid IPv6 address

Obviously, writing so many values is cumbersome, so a shorthandabbreviation has been provided.

1. runs of all zeros are not listed, a :: double colon implies thatthe values between the colons are all zero. There couldbe multiple zero fields. How many there are is calculatedby subtracting the number of digits that are present from 32, thenumber of digits in a complete address. So the above address would become:

7477::0AFF:1BDF:7FFF

2. leading zeros can also be omitted:

7477::AFF:1BDF:7FFF

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This substitution can be made only once:

Example1DFG:0000:0000:0000:EDF2:0000:0000:E123

could only be shortened to:

1DFG::EDF2:0000:0000:E123

which could further be shorted to:

1DFG::EDF2:0:0:E123

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