Ethernet Networking- P5 pps

108 Connecting to the Internet Leased Lines If you need high bandwidth that is dedicated to your use between your premises 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 fractional 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 Designation Speed Sample Cost Comments Fractional T1 256 Kpbs to 768 Kbps T 1 (also 1.5 Mbps known as DS 1) Fractional T3 10 Mbps to 40 Mpbs T3 (also called 45 Mpbs DS3) OC3 155 Mbps OC12 620 Mpbs OC48 2.5 Gbps OC 192 9.6 Gbps Under $300 per month (for example, $260 per month for 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 5 to 30 users. A full T1 supports 20 to 50 data users, up to 24 voice channels, or a mixture of both voice and data. May be cheaper than multiple Tls. 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 specific 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 service 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 point 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 therefore 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. 110 Connecting to the Internet 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 significantly 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 multiple 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 111 112 Routing 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 connectivity, 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 security 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 addresses rather than hardware-encoded MAC addresses, also provides a first-line security buffer for your internal network, handles assigning internal 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 addresses 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, although 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. 114 Routing Table 6-1: IP Address Classes Bytes in Number of Address network networks in class Address range part the class Number of nodes per network A 0.0.0.0 a to 1 126 b 127.255.255.255 B 128.0.0.0 to 2 16,384 191.255.255.255 C 192.0.0.0 to 3 2,097,152 223.255.255.255 > 16 million 65,534 254 a. 0.0.0.0 cannot be assigned to a network; it is used as a broadcast address to refer to all nodes on the current network. b. There are only 126 (rather 128) addresses in class A because 0.0.0.0 is reserved as the broadcast address and 127.0.0.1 is reserved as a loopback address to enable nodes to communicate with themselves. 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 routing; these are reserved for internal network addresses. In most cases, these are used for dynamic IP addressing and are assigned by a router to a device as it joins a network. The use of these internal addresses (and dynamic 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 Network Bytes in network class Address range portion A 10.0.0.0 to 10.255.255.255 1 B 172.16.0.0 to 172.31.255.255 2 C 192.168.0.0 to 192.168.255.255 3 For example, the machine on which I wrote this book typically has the IP address of 192.168.1.101. The first byte of the address tells you that it is a class C network; the actual value of the first byte indicates that it is an internal IP address that can't be used on the Internet. 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 connection 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 networks. 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 rate and don't forget things such as cell phones and PDAs!~it 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. 116 Routing 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 of contiguous Os that is expanded to make the address a full 128 bits. If there were more than one ::, it would be impossible to determine the number of 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 the/## notation, where ## indicates the number of bits used to identify the network, just as it does with IPv4 addresses. The network 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 Address Use/comments ::/128 ::1/128 ::/96 ::fff:0:0/96 fc00::/7 fe80::/10 if00::/8 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. [...]... 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... own specific model to determine its default configuration Applications and network protocols receive fixed 133 Adding Routers to an Ethernet port numbers Those used most commonly are called well-known ports You can find a table of them in Appendix B Adding Routers to an Ethernet When you are ready to connect your internal network to the Internet, you will need to add a router to your network As mentioned... hierarchy from that core switch Be careful when you shop for a router The small routers that sell for less than $100 have only 10/100 ports, meaning that they are limited to Fast Ethernet speeds Those with 10/100/1000 ports (up to Gigabit Ethernet) currently sell for between $100 and $200 Nonetheless, you can expect any of these routers to have a wireless access point, firewall, and switch with between one... not need a router at all: Router 131 Router Capabilities capabilities may be built into the "modem" supplied by your ISP In other words, the DSL or cable interconnection device may include a four-port Ethernet switch, wireless access point, and a firewall The drawback to this setup, however, is that the "modem"may not be configurable like a true router It may not provide VPN (virtual private network)... four-port; go for the eight-port!) Note: For more examples of actual network architectures, see Chapters 12 through 14, which contain case studies of networks of different sizes Adding Routers to an Ethernet 135 Configuring the Router Even small "home" routers are intelligent devices and provide a variety of configuration options that typically can be accessed from a Web browser The router itself... makes sense to show you the types of security that a router can provide First and foremost, most routers supply a firewall (See Figure 6-9.) You may choose to use or not use it 137 Adding Routers to an Ethernet Figure 6-8" Router status screen Figure 6-9: A router's security screen . Loopback a 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 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. 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 command would be ifconfig ethO 10.148.6.118