Ethernet Networking- P5 pps

IPv4 addresses are 32 bits long and are the primary type of address used today.. However, the people who developed the IP addressing scheme underestimated the growth of the Internet, and

Leased Lines

If you need high bandwidth that is dedicated to your use between your pre- mises and your ISP, you can consider leasing the use of a line from a tele- communications provider A leased line is a specially conditioned digital line that can support data and voice traffic

Leased lines come in varous speeds and capacities, some of which are summarized in Table 5-2 As you can see, once you move beyond a frac- tional or full T1, you're looking at much more bandwidth than a small or home business is likely to need The cost is also significant

Table 5-2: Leased Line Options

512 Kbps)

$300 to $1200 per month

Depends on bandwidth $2600 and up per month $5000 per month

$15,000 per month $80,000 a per month (Prices not publicly available)

Supports more than 100 users or upt to 672 voice channels Used by large Internet backbone providers

Used primarily for point-to- point WAN connections

Used only by the largest Internet providers

Used only by the largest Internet providers

a No, this is not a typographic error!

Direct Connections 109

Note: Specific costs for leased lines are very difficult to obtain because they depend on location, line availability, and the spe- cific services ordered The only prices you are likely to find pub- lished are T1 and fractional T1; the rest require specific quotes from service providers

Leased lines provide better privacy and security than cable access or DSL, high reliability, low error rates, support for static IP addresses, and, of course, high bandwidth They are generally also available in places where DSL and cable may not be In addition, the bandwidth of a leased line can

be shared by voice and data signals Should you have a leased line, you can probably do away with regular telephone lines

The biggest drawback to a leased line is cost Leased lines may also require

a professional to install and configure the line on your premises

Wiceless

It is possible to use a wireless connection to access the Internet, bypassing telephone and cable wires completely To obtain such a connection, you contract with a wireless ISP for service, just as you would a wired ISE A number of cable and cell phone providers also have wireless Internet ser- vice available

Note: This is different from connecting wireless devices to your internal network What we're talking about here is a wireless connection to an ISP Although some of the issues surrounding wireless Internet are the same, connecting wireless devices to your wired Ethernet is covered in Chapter 7

Wireless Internet uses radio waves to transmit data signals from terrestrial towers to a wireless access p o i n t on your premises You can then share that bandwidth across your network However, the signals do not travel well through natural or manmade objects In other words, you must have a good line-of-sight to a tower to receive the signal Most wireless providers there- fore are limited to a small geographic area Generally, service is available

in densely populated metropolitan areas, but is fairly sparse in small towns and rural areas

Wireless Pluses and Minuses

There are several benefits to having wireless connectivity to your business

or home network:

You avoid relying on a wired solution Your employees can connect from anywhere in your ISP's service area, as well as from your internal network

Cost is reasonable (comparable to DSL and cable)

Installation and maintenance are simple

However, there are some significant drawbacks to wireless Internet service

as well:

Wireless data rates are significantly slower than wired data rates Although current wireless services are based on stan- dards that support speeds up to 54 Mbps, actual speeds are sig- nificantly slower, as slow as 2 Mbps The chances of obtaining anywhere near the maximum speed are very slim (More on this in Chapter 7.)

Service is not available in many areas, and when service is available, it is limited to a relatively small geographic area The idea that you could have one wireless Internet provider that you could use anywhere in the country is very appealing, but not re- alistic For example, Verizon, one of the largest wireless Inter- net providers in this country, has wireless Internet connectivity

in 181 metropolitan areas They continue to expand their offer- ings, but they are many years away from nationwide coverage Even if you are within a wireless ISP's service area, you may not be able to pick up a wireless Internet signal if there are physical obstacles blocking your line-of-sight to a tower that relays the wireless signal

Wireless networking has serious security vulnerabilities (In fact, many people consider these vulnerabilities so serious that this issue should be the first drawback listed, rather than the last.)

Note: We will look at the security issues surrounding wireless networking in some depth in Chapters 7 and 10

Routing

As we've been discussing, you use a switch (or a hub, if you must) to create

a single network segment You use a hierarchy of switches to create multi- ple segments, generally to improve performance by spreading the traffic over the multiple segments If such a network has no outside connectivity (in other words, if it doesn't connect to any type of WAN), then you can give each device a unique static IP address of your choice and all will work well However, if you need WAN connectivity, then the situation becomes more complicated:

The IP addresses must be unique across the entire WAN, which, in most cases, means the Internet How are you going to ensure that you don't duplicate an IP address in use somewhere else in the world?

Switches work with MAC addresses, unique identifiers that are part of network hardware How can you send a message over the Internet to a device whose MAC address is unknown and

111

unknowable? (Remember that switches learn the location of MAC addresses as messages pass through them They can't possibly gain access to MAC addresses of devices that aren't

on the same network; the Internet is in the way!)

0 Opening up your network to a WAN makes it significantly more vulnerable to security problems Without Internet con- nectivity, you generally only need to worry about what your end users are doing But when the Internet enters the picture, the entire world of security problems becomes your concern (End users are responsible for at least half the security breaches that occur, so adding Internet connectivity can double your se- curity headaches.)

The solution is a device known as a router In most cases, a small network will need only one (an edge router), which acts as an interface between In- ternet traffic coming from an ISP and your internal network It will then be the router that actually makes the connection to the ISP through a single WAN port It provides a single point of connectivity to a WAN

The router, which directs messages based on the software-assigned IP ad- dresses rather than hardware-encoded MAC addresses, also provides a first-line security buffer for your internal network, handles assigning inter- nal dynamic IP addresses, and directs traffic to the correct devices on the internal network

Routers (once known as gateways) are part of the system of IP addresses and associated domain names that drive the Internet Most function at layer

3 of the joint TCP/IP and OSI protocol stack (the Network layer) To understand how a router works and how its function differs from that of a switch, we have to begin by talking about IP addresses in some depth and about domain names

IP Addressing

IP addresses are software addresses Although we've said that each device connected to the Internet must have a unique IP address, that doesn't mean that the IP address must be hard-wired to the device or that it must always

IP Addressing 113

be the same IP addresses can be changed as needed, and because they are assigned either through a device's operating system or by a router, having them in software provides the necessary flexibility Flexibility is particu- larly important because devices enter and leave a network frequently, as they start up, shut down, sleep, and wake up

There are two schemes for IP addressing: IPv4 and IPv6 IPv4 addresses are 32 bits long and are the primary type of address used today However, the people who developed the IP addressing scheme underestimated the growth of the Internet, and we are running out of unique IPv4 addresses IPv4 provides only 4.3 billion (4.3 * 109) unique addresses, fewer address-

es than the number of people on this planet!

IPv6 addresses are 128 bits long and are slowly being phased in The 128 bits can provide 50 octillion (5 * 1028) addresses However, initial predi- cations were that we would run out of IPv4 adresses by 1980; at the time this book was written, the prediction had been moved ahead to 2013 Meanwhile, both forms of IP addresses are coexisting on the Internet, al- though there are very few IPv6 addresses in use

IPv4 Addressing

To makes IPv4 addresses easier to read, we typically group the bits in the address into four sections and write it in the format X.X.X.X (dot-decimal notation), where each X is a value between 0 and 255 (a byte) The first

one, two, or three Xs represent the network part of the address because

they identify an entire network The number of bytes used as the network part of an IPv4 address indicates the class of the network and limits both the number of unique networks allowed in that class and the number of nodes supported per network In Table 6-1, you can see the three classes of networks currently in use

Note: Class D addresses (224.0.0.0 to 239.255.255.255) are reserved for multicasting (broadcasts within prespec- ified groups of addresses) Class E addresses (240.0.0.0

to 247.255.255.255) are reserved for future use

Table 6-1: IP Address Classes

Bytes in Number of

class Address range part the class

Number of nodes per network

Not all IPv4 addresses are designed for external Internet use In Table 6-2 you will find ranges of IPv4 addresses that cannot be used for Internet rout- ing; these are reserved for internal network addresses In m o s t cases, these are used for d y n a m i c IP addressing and are assigned by a router to a device

as it joins a network The use of these internal addresses (and d y n a m i c IP addressing in general) has slowed the use of unique static IP addresses, helping to extend the life of IPv4

Table 6-2: IPv4 Address Spaces for Internal Networks

IP Addressing 115

The network portion of an IPv4 address may also identify a subnet, a

switched network segment attached to a router As an example, take a look

at Figure 6-1 This network has a single router providing a shared connec- tion to the Internet The router actually has four network interfaces, one for whatever device is providing the interface to the Internet service and three

to connect to switches Each switch connects to its own network, a subnet Notice the IP addresses: The first two bytes (also known as octets) are the same throughout the entire entwork, the 192.168 used for internal net- works However, the third octet is unique to each subnet and therefore identifies the subnet to which a device is connected

The remaining numbers uniquely identify a network device (the hostpart)

In Figure 6-1, each host part is unique within its own subnet Notice that the host parts can duplicate, as long as the entire IP address is unique

To extend the life of IPv4 addressing, some networks allocate the bits in the IP address in a different way (classless addressing) You can recognize such an address because it ends with a / (slash) and a number For example, 192.168.124.18/22 tells you that the first 22 bits of the IP address are being used as the network portion and that the last 10 represent the host

IPvd Addressing

It makes economic sense to extend the life of IPv4 as much as possible: The majority of existing routing equipment hasn't been programmed to deal with IPv6 addressing and the cost of replacing the equipment would

be substantial Nonetheless, if the increase in devices that connect to the Internet continues at anywhere near the current r a t e - - a n d don't forget things such as cell phones and P D A s ! ~ i t is inevitable that we'll need the longer addressing scheme

Rather than decimal numbers to represent IPv6 addresses for human con- sumption, we use eight groups of four hexadecimal digits For example, fe80:0000:0000:0000:0214:51ff:fe64:833 is the full IPv6 address of my main publishing workstation; to shorten it, the address can be abbreviated

as fe80::0214:51ff:fe64:833f by removing contiguous groups that are all 0s and replacing them with a single extra colon

Figure 6-1: A network with one router and multiple switched segments

Note: There can be only one :: in an IPv6 address It re- places a string o f contiguous Os that is expanded to make the address a full 128 bits I f there were more than one ::,

it would be impossible to determine the number o f Os to in- sert when expanding the address

Getting an IP Address 117

Table 6-3:

Originally, the first 64 bits in an IPv6 address were allocated to identifying the network; the remaining 64 identified the host However, other alloca- tions are used with t h e / # # notation, where ## indicates the number of bits used to identify the network, just as it does with IPv4 addresses The net- work portion is also known as the address's prefix A network (or subnet)

is therefore a group of IPv6 addresses with the same prefix

IPv6 networks have no classes However, some addresses have special pur- poses (See Table 6-3.)

Special Purpose IPv6 Addresses

All 0s means an unspecified address; for use only by software

The IPv6 loopback address; expands to all 0s except for a 1 in the right- most bit

The prefix is 32 bits of 0s, used for IPv4 compatibility

A 32-bit prefix used for mapping IPv4 addresses

Nonroutable addresses for use on an internal network, similar to the IPv4 addresses in Table 6-2

A 10-bit prefix that restricts the use of the address to the current physical link (i.e., the current subnet, if applicable)

An 8-bit prefix indicating a multicast packet, a

a IPv6 does not have a separate broadcast address Instead, you would send a multicast message addressed to "all hosts."

Important note: From this point on, unless we state otherwise, all references to an IP address mean an IPv4 address

Getting an IP Address

Throughout this chapter we've mentioned that IP addresses come from ISPs That is true in the sense that your IP address, whether static or dynamic, does come from your ISP But where does your ISP get IP addresses? And how does your computer actually get one? That's what this section is all about

ISPs and r p Addresses

Ultimate responsibility for assigning IP numbers rests with the Internet Assigned Numbers Authority (IANA) However, numbers are actually as- signed by regional registries In the United States, for example, registration

is handled by the American Registry for Internet Numbers (ARIN) IP numbers are assigned in large blocks to ISPs

ARIN will also assign blocks of IP addresses to end users, but at this time,

it seems reluctant to do so"

Assignments of IPv4 address space are made to end-user organizations or individuals for use in running internal networks, and not for sub-delegation of those addresses outside their organization End-users not currently con- nected to an ISP and/or who do not plan to be connected

to the Internet are encouraged to use private IP numbers reserved for non-connected networks

Source: http ://www.arin.net

The private IP numbers to which the quote refers are the ranges of non- routable addresses in Table 6-2 This is part of the global strategy to extend the life of IPv4 addresses

Note: Blocks of IP addresses are not free Depending on the size of the block allocated, an ISP pays from $1,250 to

$18,000 per year An end user pays an initial fee of $1,250

to $18,000 (again dependent on the size of the block of ad- dresses) plus a $100 annual maintenance fee Add in the cost of T3 lines, and setting yourself up as an ISP begins

to look like a very expensive business.t

Static IP Addresses

If you want to host your own Web site, you will need a static IP address You will be given this address by your ISP You must then manually con- figure the server to use this address How you do so depends on your oper- ating system

Getting an IP Address 119

Windows

You can set a static IP address for a Windows machine through the GUI, although finding the fight place to enter the address takes a bit of digging

As it so happens, the path for both XP and 2000 is exactly the same:

1 Follow the path My Computer->Control Panel->Network and Dial-up Connections or Network Connections

2 Open the icon for the interface for which you want to set the IP ad- dress

3 Choose Internet Protocol (TCP/IP) to display the correct dialog box

4 Click on the Use the following IP address radio button (See Figure 6-2.)

5 Enter the IP address in the appropriate text box and save the changes

Figure 6-2: Setting a static IP address for Windows XP (left) and 2000 (right)

Note: You will also need to enter a subnet mask, which we'll discuss in a later section in this chapter

Macintosh OS X

Entering a static IP address for a Mac OS X machine is not significantly different from doing so for a Windows machine; it's just not buried as deep:

1 Launch System Preferences and open the Network preferences panel

2 Highlight the interface for which you want to enter a static IP address and click the Configure button

3 Choose Manually from the Configure IPv4 popup menu (See Figure 6-3.)

4 Enter the IP address in the appropriate text box and save the changes

Linux

Figure 6-3: Entering a Mac OS X static IP address

Many Linux distributions ease the assigning of a static IP address through the GUI used to install the operating system However, if you need to set

Getting an IP Address 121

the IP address from the command line, you'll need to use the ifconfig com- mand to set up at least two network interfaces (loopback and one other) for your machine It has the general syntax

ifconfig type_of_interface IP_address

The type of interface is the name of the device driver for the interface The ones you are likely to need can be found in Table 6-4

Table 6-4: Linux Network Interface Driver Names

PPP PPP (Point-to-Point protocol, used for dial-up connections)

ethX Ethernet, where X is the number of the Ethernet interface If

you have only one network adapter, it will be ethO A second adapter will be ethl, and so on

a Loopback addresses take the form 127.X.X.X Once a loopback address has been configured, a line for localhost (usually with the IP address of 127.0.01) can be found in the/etc/hosts file

For example, if I want my Ethernet adapter to have the IP address of 10.148.6.118, the c o m m a n d would be

ifconfig ethO 10.148.6.118

The ifconfig commands makes the interface active The next step is to add the interface to the Linux kernel's routing table so that your machine can find other computers"

route add IP_address

To add the preceding Ethemet interface, you would use

route add 10.148.6.188

Note: To remove an IP address from the kernel's routing table, issue the route command again, substituting "del"

DHCP and BootP

There are two protocols in wide use for assigning dynamic IP addresses, DHCP (Dynamic Host Configuration Protocol) and BootP (Bootstrap Pro- tocol) These Network layer protocols typically give a device a new IP address when it connects to a network Both require "servers" running the protocols to issue IP addresses However, for a small network, the servers are built in to most small routers; you don't need a standalone machine act- ing as a DCHP or BootP server

Dynamic Host Configuration Protocol

DHCP allocates IP addresses in one of three ways:

$ Manual allocation: The device running DHCP (a server or router) has a table that pairs MAC addresses with IP addresses Whenever a device powers up and enters the network, it re- quests an IP address from DHCP DHCP looks up the MAC ad- dress in its table and issues the associated IP address If the MAC address isn't in the table, the device doesn't get an IP ad- dress and therefore isn't allowed on the network The setup of manual allocation is time consuming for a network administra- tor, but does provide a measure of security because only autho- rized devices can connect