Windows Server 2012 R2 - Chapter 4

Windows Server 2012 R2 - Chapter 4

1. Objective 4.1: Configure IPv4 and IPv6 addressing

   • IPv4 addressing
     • As you probably know, The IPv4 address space consists of 32-bit addresses, notated as four 8-bit decimal values from 0 to 255 and separated by periods (for example, 192.168.43.100). This is known as dotted-decimal notation and the individual 8-bit decimal values are called octets or bytes.
       • To differentiate the network bits from the host bits, each address must have a subnet mask. A subnet mask is another 32-bit value consisting of binary 1 bits and 0 bits. When compared to an IP address, the bits corresponding to the 1s in the mask are the network bits, and the bits corresponding to the 0s are the host bits. Thus, if the 192.168.43.100 address mentioned earlier has a subnet mask of 255.255.255.0 (which in binary form is 11111111.11111111.11111111.00000000), the first three octets (192.168.43) identify the network and the last octet (100) identifies the host.
     • IPv4 classful addressing
       • Because the subnet mask associated with IP addresses can vary, the number of bits used to identify the network and the host can also vary. The original IP standard defines three classes of IP addresses, which support networks of different sizes,
         • The number of networks and hosts supported by each of the address classes are listed in Table 4-1.
           • The values in Table 4-1 for the number of hosts each address class supports might appear low. For example, an 8-bit binary number can have 256 (that is, 28) possible values, not 254, as shown in the table for the number of hosts on a Class C address. The value 254 is used because the original IP addressing standard states that you can’t assign the “all zeros” or “all ones” addresses to individual hosts. The “all zeros” address identifies the local network, not a specific host, and the “all ones” identifier always signifies a broadcast address. You cannot assign either value to an individual host. Therefore, to calculate the number of possible network or host addresses you can create with a given number of bits, you use the formula 2x–2, where x is the number of bits.
       • In addition to Classes A, B, and C, the IP standard defines Class D and Class E. Class D addresses begin with the bit values 1110 and Class E addresses begin with 11110. The Internet Assigned Numbers Authority (IANA) has allocated Class D addresses for use as multicast identifiers. A multicast address identifies a group of computers on a network, all of which possess a similar trait. Multicast addresses enable TCP/IP applications to send traffic to computers that perform specific functions (such as all the routers on the network), even if they’re located on different subnets. Class E addresses are defined as experimental and are as yet unused.
       • Classless Inter-Domain Routing
         • classful addressing was gradually obsolesced by a series of subnetting methods, including variable length subnet masking (VLSM) and eventually Classless Inter-Domain Routing (CIDR). CIDR is a subnetting method that enables administrators to place the division between the network bits and the host bits anywhere in the address, not just between octets. This makes it possible to create networks of almost any size.
           • CIDR also introduces a new notation for network addresses. A standard dotted-decimal address representing the network is followed by a forward slash and a numeral specifying the size of the network-identifying prefix. For example, 192.168.43.0/24 represents a single Class C network that uses a 24-bit network identifier, leaving the other 8 bits for up to 254 host identifiers. Each of those hosts would receive an address from 192.168.43.1 to 192.168.43.254, using the subnet mask 255.255.255.0.
             • However, by using CIDR, an administrator can subnet this address further by allocating some of the host bits to create subnets. To create subnets for four offices, for example, the administrator can take two of the host identifier bits, changing the network address in CIDR notation to 192.168.43.0/26. Because the network identifier is now 26 bits, the subnet masks for all four networks will now be 11111111.11111111.11111111.11000000 in binary form, or 255.255.255.192 in standard decimal form. Each of the four networks will have up to 62 hosts, using the IP address ranges shown in Table 4-2.
               • If the administrator needs more than four subnets, changing the network address to 192.168.43.0/28 adds two more bits to the network address for a maximum of 16 subnets, each of which can support up to 14 hosts. The subnet mask for these networks would therefore be 255.255.255.240.
       • Public and private IPv4 addressing
         • The IANA is the ultimate source for all registered addresses. Managed by the Internet Corporation for Assigned Names and Numbers (ICANN), this organization allocates blocks of addresses to regional Internet registries (RIR), which, in turn, allocate smaller blocks to Internet service providers (ISPs). An organization that wants to host a server on the Internet typically obtains a registered address from an ISP.
           • Private IP addresses are blocks of addresses that are allocated specifically for private network use. Anyone can use these addresses without registering them, but they cannot make computers using private addresses accessible from the Internet without using a specialized technology such as network address translation (NAT). The three blocks of addresses allocated for private use are as follows: ■■ 10.0.0.0/8 ■■ 172.16.0.0/12 ■■ 192.168.0.0/16
             • Most enterprise networks use addresses from these blocks for their workstations. It doesn’t matter if multiple organizations use the same addresses, because the workstations are never directly connected to the same network.
     • IPv4 subnetting
       • In most cases, enterprise administrators use addresses in one of the private IP address ranges to create the subnets they need. If you are building a new enterprise network from scratch, you can choose any one of the private address blocks and make things easy on yourself by subnetting along the octet boundaries.
         • For example, you can take the 10.0.0.0/8 private IP address range and use the entire second octet as a subnet ID. This enables you to create up to 256 subnets with as many as 65,536 hosts on each one. The subnet masks for all the addresses on the subnets will be 255.255.0.0 and the network addresses will proceed as follows: ■■ 10.0.0.0/16 ■■ 10.1.0.0/16 ■■ 10.2.0.0/16 ■■ 10.3.0.0/16 ■■ … ■■ 10.255.0.0/16
           • When you are working on an existing network, the subnetting process is likely to be more difficult. You might, for example, be given a relatively small range of addresses and be asked to create a certain number of subnets from them. To do this, you use the following procedure.
             • 1. Determine how many subnet identifier bits you need to create the required number of subnets.
               • 2. Subtract the subnet bits you need from the host bits and add them to the network bits.
                 • 3. Calculate the subnet mask by adding the network and subnet bits in binary form and converting the binary value to decimal.
                   • 4. Take the least significant subnet bit and the host bits, in binary form, and convert them to a decimal value.
                     • 5. Increment the network identifier (including the subnet bits) by the decimal value you calculated to determine the network addresses of your new subnets.
             • Using the example earlier in this chapter, if you take the 192.168.43.0/24 network address and allocate two extra bits for the subnet ID, you get a binary subnet mask value of 11111111.11111111.11111111.11000000 (255.255.255.192 in decimal form, as noted earlier).
               • The least significant subnet bit plus the host bits gives you a binary value of 1000000, which converts to a decimal value of 64. Therefore, if you know that the network address of your first subnet is 192.168.43.0, the second subnet must be 192.168.43.64, the third 192.168.43.128, and the fourth 192.168.43.192, as shown in Table 4-2.
     • Supernetting
       • In addition to simplifying network notation, CIDR also makes possible a technique called IP address aggregation or supernetting, which can help reduce the size of Internet routing tables. A supernet is a combination of contiguous networks that all contain a common CIDR prefix. When an organization possesses multiple contiguous networks that can be expressed as a supernet, it is possible to list those networks in a routing table by using only one entry instead of many.
         • For example, if an organization has the following five subnets, standard practice would be to create a separate routing table entry for each one.
           • To create a supernet encompassing all five of these networks, you must isolate the bits they have in common. When you convert the network addresses from decimal to binary, you get the following values:
             • 172.16.43.0 10101100.00010000.00101011.00000000 172.16.44.0 10101100.00010000.00101100.00000000 172.16.45.0 10101100.00010000.00101101.00000000 172.16.46.0 10101100.00010000.00101110.00000000 172.16.47.0 10101100.00010000.00101111.00000000
             • In binary form, you can see that all five addresses have the same first 21 bits. Those 21 bits become the network identifier of the supernet address, as follows:
               • 10101100.00010000.00101
               • After zeroing out the host bits to form the network address and converting the binary number back to decimal form, as follows, the resulting supernet address is 172.16.40.0/21.
                 • 10101100.00010000.00101000.00000000 172.16.40.0/21
                 • This one network address can replace the original five in routing tables duplicated throughout the Internet. This is just one example of a technique that administrators can use to combine dozens or even hundreds of subnets into single routing table entries.
           • ■■ 172.16.43.0/24 ■■ 172.16.44.0/24 ■■ 172.16.45.0/24 ■■ 172.16.46.0/24 ■■ 172.16.47.0/24
     • Assigning IPv4 addresses
       • In addition to understanding how IP addressing works, a network administrator must be familiar with the methods for deploying IP addresses to the computers on a network. To assign IPv4 addresses, there are three basic methods:
         • ■■ Manual configuration ■■ Dynamic Host Configuration Protocol (DHCP) ■■ Automatic Private IP Addressing (APIPA)
       • MANUAL IPV4 ADDRESS CONFIGURATION
         • To configure IP address settings in Windows Server 2012 R2, you use the Internet Protocol Version 4 (TCP/IPv4) Properties sheet
           • When you select the Use The Following IP Address option, you can configure the following IP address options:
             • IP Address
               • Specifies the IP address on the local subnet that will identify the network interface in the computer
             • Subnet Mask
               • Specifies the mask associated with the local subnet
             • Default Gateway
               • Specifies the IP address of a router on the local subnet, which the system will use to access destinations on other networks
             • Preferred DNS Server
               • Specifies the IP address of the DNS server the system will use to resolve host names into IP addresses
       • DYNAMIC HOST CONFIGURATION PROTOCOL (DHCP)
         • DHCP is an application-layer protocol that together enable administrators to dynamically allocate IP addresses from a pool. Computers equipped with DHCP clients automatically contact a DHCP server when they start, and the server assigns them unique addresses and all the other configuration parameters the server is configured to provide.
           • The DHCP server provides addresses to clients on a leased basis, and after a predetermined interval, each client either renews its address or releases it back to the server for reallocation. DHCP not only automates the address assignment process but also keeps track of the addresses it assigns, preventing address duplication on the network.
       • AUTOMATIC PRIVATE IP ADDRESSING (APIPA)
         • APIPA is the name assigned by Microsoft to a DHCP failover mechanism used by all the current Microsoft Windows operating systems. On Windows computers, the DHCP client is enabled by default. If, after several attempts, a system fails to locate a DHCP server on the network, APIPA takes over and automatically assigns an address on the 169.254.0.0/16 network to the computer.
           • For a small network that consists of only a single local area network (LAN), APIPA is a simple and effective alternative to installing a DHCP server. However, for installations consisting of multiple LANs connected by routers, administrators must take more positive control over the IP address assignment process. This usually means deploying one or more DHCP servers in some form.
   • IPv6 addressing
     • Introducing IPv6
       • IPv6 addresses are different from IPv4 addresses in many ways other than length. Instead of the four 8-bit decimal numbers separated by periods that IPv4 uses, IPv6 addresses use a notation called colon-hexadecimal format, which consists of eight 16-bit hexadecimal numbers separated by colons, as follows:
         • XX:XX:XX:XX:XX:XX:XX:XX
         • Each X represents eight bits (or one byte), which in hexadecimal notation is represented by two characters, as in the following example:
           • 21cd:0053:0000:0000:e8bb:04f2:003c:c394
       • CONTRACTING IPV6 ADDRESSES
         • When an IPv6 address has two or more consecutive 8-bit blocks of zeros, you can replace them with a double colon, as follows (but you can use only one double colon in any IPv6 address):
           • 21cd:0053::e8bb:04f2:003c:c394
           • You can also remove the leading zeros in any block where they appear, as follows:
             • 21cd:53::e8bb:4f2:3c:c394
       • EXPRESSING IPV6 NETWORK ADDRESSES
         • There are no subnet masks in IPv6. Network addresses use the same slash notation as CIDR to identify the network bits. In this example, the network address is notated as follows:
           • 21cd:53::/64
           • This is the contracted form for the following network address:
             • 21cd:0053:0000:0000/64
     • As most administrators know, IPv6 is designed to increase the size of the IP address space, thus providing addresses for many more devices than IPv4. The 128-bit address size of IPv6 allows for 2128 possible addresses—which is over 54 million addresses for each square meter of the Earth’s surface.
       • In addition to providing more addresses, IPv6 will also reduce the size of the routing tables in the routers scattered around the Internet. This is because the size of the addresses provides for more than the two levels of subnetting currently possible with IPv4.
     • IPv6 address types
       • There are no broadcast transmissions in IPv6, and therefore no broadcast addresses, as in IPv4. IPv6 supports three types of transmissions, as follows:
         • Unicast
           • Provides one-to-one transmission service to individual interfaces, including server farms sharing a single address
           • GLOBAL UNICAST ADDRESSES
             • A global unicast address is the equivalent of a registered IPv4 address, routable worldwide and unique on the Internet.
           • LINK-LOCAL UNICAST ADDRESSES
             • In IPv6, systems that assign themselves an address automatically create a link-local unicast address, which is essentially the equivalent of an APIPA address in IPv4. All link-local addresses have the same network identifier: a 10-bit prefix of 1111111010 followed by 54 zeros, resulting in the following network address:
               • fe80:0000:0000:0000/64
               • In its more compact form, the link-local network address is as follows:
                 • fe80::/64
               • Because all link-local addresses are on the same network, they are not routable, and systems possessing them can only communicate with other systems on the same link.
           • UNIQUE LOCAL UNICAST ADDRESSES
             • Unique local unicast addresses are the IPv6 equivalent of the 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16 private network addresses in IPv4. Like the IPv4 private addresses, unique local addresses are routable within an organization. Administrators can also subnet them as needed to support an organization of any size.
         • Multicast
           • Provides one-to-many transmission service to groups of interfaces identified by a single multicast address
           • Multicast addresses always begin with a value of 11111111 in binary, or ff in hexadecimal.
         • Anycast
           • Provides one-to-one-of-many transmission service to groups of interfaces, only the nearest of which (measured by the number of intermediate routers) receives the transmission
           • ANYCAST ADDRESSES The function of an anycast address is to identify the routers within a given address scope and send traffic to the nearest router, as determined by the local routing protocols. Organizations can use anycast addresses to identify a particular set of routers in the enterprise, such as those that provide access to the Internet. To use anycasts, the routers must be configured to recognize the anycast addresses as such.
     • Assigning IPv6 addresses
       • As with IPv4, a Windows computer can obtain an IPv6 address by three possible methods:
         • Manual allocation
           • A user or administrator manually supplies an address and other information for each network interface.
           • The computer solicits and receives an address from a DHCPv6 server on the network.
             • For the enterprise administrator, manual allocation of addresses is even more impractical in IPv6 than in IPv4 because of the length of the addresses involved. However, it is possible, and the procedure for doing so in Windows Server 2012 R2 is the same as that for IPv4, except that you open the Internet Protocol Version 6 (TCP/IPv6) Properties sheet,
         • Dynamic allocation
           • The computer solicits and receives an address from a DHCPv6 server on the network.
           • DYNAMIC HOST CONFIGURATION PROTOCOL V6
             • The Remote Access role in Windows Server 2012 R2 supports IPv6 routing and advertising, and the DHCP Server role supports IPv6 address allocation.
         • Self-allocation
           • The computer creates its own address by using a process called stateless address autoconfiguration.
           • STATELESS IPV6 ADDRESS AUTOCONFIGURATION
             • When a Windows computer starts, it initiates the stateless address autoconfiguration process, during which it assigns each interface a link-local unicast address. This assignment always occurs, even when the interface is to receive a global unicast address later. The link-local address enables the system to communicate with the router on the link, which provides additional instructions. The steps of the stateless address autoconfiguration process are as follows.
               • 1. Link-local address creation
                 • The IPv6 implementation on the system creates a linklocal address for each interface by using the fe80::/64 network address and generating an interface ID, either by using the interface’s media access control (MAC) address or a pseudorandom generator.
               • 2. Duplicate address detection
                 • Using the IPv6 Neighbor Discovery (ND) protocol, the system transmits a Neighbor Solicitation message to determine if any other computer on the link is using the same address and listens for a Neighbor Advertisement message sent in reply. If there is no reply, the system considers the address to be unique on the link. If there is a reply, the system must generate a new address and repeat the procedure.
               • 3. Link-local address assignment
                 • When the system determines that the link-local address is unique, it configures the interface to use that address. On a small network consisting of a single segment or link, this might be the interface’s permanent address assignment. On a network with multiple subnets, the primary function of the link-local address assignment is to enable the system to communicate with a router on the link.
               • 4. Router advertisement solicitation
                 • The system uses the ND protocol to transmit Router Solicitation messages to the all routers multicast address. These messages compel routers to transmit the Router Advertisement messages more frequently.
               • 5. Router advertisement
                 • The router on the link uses the ND protocol to transmit Router Advertisement messages to the system, which contain information on how the autoconfiguration process should proceed. The Router Advertisement messages typically supply a network prefix, which the system will use with its existing interface ID to create a global or unique local unicast address. The messages might also instruct the system to initiate a stateful autoconfiguration process by contacting a specific DHCPv6 server. If there is no router on the link, as determined by the system’s failure to receive Router Advertisement messages, then the system must attempt to initiate a stateless autoconfiguration process.
               • 6. Global or unique local address configuration
                 • Using the information it receives from the router, the system generates a suitable address that is routable, either globally or within the enterprise, and configures the interface to use it. If so instructed, the system might also initiate a stateful autoconfiguration process by contacting the DHCPv6 server specified by the router and obtaining a global or unique local address from that server, along with other configuration settings.
       • Subnetting IPv6 Addresses
         • As with IPv4, administrators can create a hierarchy of subnets using IPv6 addresses. However, in IPv6, no subnet masks are needed because there are ample bits in the network identifier to create a subnet identifier without having to borrow from the host bits.
           • The format for an IPv6 global unicast address divides the 128 bits into the following three sections:
             • Global routing prefix
               • A 48-bit field beginning with the 001 FP value, the hierarchical structure of which is left up to the regional Internet registry (RIR)
             • Subnet ID
               • A 16-bit field that organizations can use to create an internal hierarchy of subnets
             • Interface ID
               • A 64-bit field identifying a specific interface on the network
             • When you obtain an IPv6 network address from an ISP or an RIR, you typically get the global routing prefix, commonly known as a “/48”. You are then left with the subnet ID field to use for subnetting the network as you wish. Some possible subnetting options are as follows:
               • One-level subnet
                 • By setting all subnet ID bits to 0, all the computers in the organization are part of a single subnet.
               • Two-level subnet
                 • By creating a series of 16-bit values, you can split the network into as many as 65,536 subnets. This is the functional equivalent of IPv4 subnetting, but with a much larger subnet address space.
               • Multi-level subnet
                 • By allocating specific numbers of subnet ID bits, you can create multiple levels of subnets, sub-subnets, and sub-sub-subnets, suitable for an enterprise of almost any size.
       • Tunneling
         • The primary method for transmitting IPv6 traffic over an IPv4 network is called tunneling. Tunneling, in this case, is the process by which a system encapsulates an IPv6 datagram within an IPv4 packet. The system then transmits the IPv4 packet to its destination, with none of the intermediate systems aware of the packet’s contents.
           • Tunneling can work in a variety of configurations, depending on the network infrastructure, including router-to-router, host-to-host, router-to-host, and host-to-router. However, the most common configuration is router-to-router,
         • CONFIGURING TUNNELS MANUALLY
           • It is possible to manually create semipermanent tunnels that carry IPv6 traffic through an IPv4-only network. When a computer running Windows Server 2012 R2 or Windows 8.1 is functioning as one end of the tunnel, you can use the following command:
             • netsh interface ipv6 add v6v4tunnel “interface” localaddress remoteaddress
             • In this command, interface is a friendly name you want to assign to the tunnel you are creating; localaddress and remoteaddress are the IPv4 addresses forming the two ends of the tunnel. An example of an actual command would be as follows:
               • netsh interface ipv6 add v6v4tunnel “tunnel” 206.73.118.19 157.54.206.43
         • CONFIGURING TUNNELS AUTOMATICALLY
           • There are also a number of mechanisms that automatically create tunnels over IPv4 connections. These are technologies designed to be temporary solutions during the transition from IPv4 to IPv6. All of them include a mechanism for expressing an IPv4 address in the IPv6 format. The IPv4-to-IPv6 transition technologies that Windows supports are described in the following sections.
             • 6TO4
               • The 6to4 mechanism essentially incorporates the IPv4 connections in a network into the IPv6 infrastructure by defining a method for expressing IPv4 addresses in IPv6 format and encapsulating IPv6 traffic into IPv4 packets.
             • ISATAP
               • Intra-Site Automatic Tunnel Addressing Protocol (ISATAP) is an automatic tunneling protocol used by the Windows workstation operating systems that emulates an IPv6 link by using an IPv4 network.
                 • ISATAP also converts IPv4 addresses into the IPv6 link-layer address format, but it uses a different method than 6to4. ISATAP does not support multicasting, so it cannot locate routers in the usual manner by using the Neighbor Discovery protocol. Instead, the system compiles a potential routers list (PRL) by using DNS queries and sends Router Discovery messages to them on a regular basis by using Internet Control Message Protocol version 6 (ICMPv6).
             • TEREDO
               • To use 6to4 tunneling, both endpoints of the tunnel must have registered IPv4 addresses. However, on many networks, the system that would function as the endpoint is located behind a NAT router, and therefore has an unregistered address. In such a case, the only registered address available is assigned to the NAT router itself, and unless the router supports 6to4 (which many don’t), it is impossible to establish the tunnel.
                 • Teredo is a mechanism that addresses this shortcoming by enabling devices behind non-IPv6 NAT routers to function as tunnel endpoints. To do this, Teredo encapsulates IPv6 packets within transport-layer User Datagram Protocol (UDP) datagrams rather than networklayer IPv4 datagrams, as 6to4 does.
                   • For a Teredo client to function as a tunnel endpoint, it must have access to a Teredo server, with which it exchanges Router Solicitation messages and Router Advertisement messages to determine whether the client is located behind a NAT router.
                     • To initiate communications, a Teredo client exchanges null packets called bubbles with the desired destination, using the Teredo servers at each end as intermediaries. The function of the bubble messages is to create mappings for both computers in each other’s NAT routers.

2. Objective 4.2: Configure servers

   • Understanding DHCP
     • DHCP is a service that automatically configures the IP address and other TCP/IP settings on network computers by assigning addresses from a pool (called a scope) and reclaiming them when their leases expire. Aside from being a time-consuming chore, manually configuring TCP/IP clients can result in typographical errors that cause addressing conflicts that interrupt network communications. DHCP prevents these errors and provides many other advantages, including automatic assignment of new addresses when computers are moved from one subnet to another and automatic reclamation of addresses that are no longer in use.
       • DHCP consists of three components, as follows:
         • A DHCP service, which responds to client requests for TCP/IP configuration settings
         • A DHCP client, which issues requests to servers and applies the TCP/IP configuration settings it receives to the local computer
         • A DHCP communications protocol, which defines the formats and sequences of the messages exchanged by DHCP clients and servers
     • The DHCP standards define three different IP address allocation methods:
       • Dynamic allocation
         • The DHCP server assigns an IP address to a client computer from a scope for a specified length of time. Each client must periodically renew the lease to continue using the address. If the client allows the lease to expire, the address is returned to the scope for reassignment to another client.
       • Automatic allocation
         • The DHCP server permanently assigns an IP address to a client computer from a scope. Once the DHCP server assigns the address to the client, the only way to change it is to manually reconfigure the computer.
       • Manual allocation
         • The DHCP server permanently assigns a specific IP address to a specific computer on the network. In the Microsoft DHCP server, manually allocated addresses are called reservations.
       • In addition to IP addresses, DHCP can provide clients with values for the other parameters needed to configure a TCP/IP client, including a subnet mask, default gateway, and DNS server addresses. The object is to eliminate the need for any manual TCP/IP configuration on a client system.
         • DHCP communications use eight types of messages, each of which uses the same basic packet format. DHCP traffic is carried within standard UDP/IP datagrams, using port 67 at the server and port 68 at the client.
     • DHCP options
       • Some of the most commonly-used options are described in the following sections.
         • THE DHCP MESSAGE TYPE OPTION
           • The DHCP Message Type option identifies the overall function of the DHCP message and is required in all DHCP packets. The DHCP communication protocol defines eight message types, as follows:
             • DHCPDISCOVER
               • Used by clients to request configuration parameters from a DHCP server
             • DHCPOFFER
               • Used by servers to offer IP addresses to requesting clients
             • DHCPREQUEST
               • Used by clients to accept or renew an IP address assignment
             • DHCPACK
               • Used by servers to acknowledge a client’s acceptance of an offered IP address
             • DHCPNAK
               • Used by servers to reject a client’s acceptance of an offered IP address
             • DHCPRELEASE
               • Used by clients to terminate an IP address lease
             • DHCPINFORM
               • Used by clients to obtain additional TCP/IP configuration parameters from a server
         • BOOTP VENDOR INFORMATION EXTENSIONS
           • These options include many of the basic TCP/IP configuration parameters used by most client systems, such as the following:
             • Subnet Mask
               • Specifies which bits of the IP address identify the host system and which bits identify the network where the host system resides
             • Router
               • Specifies the IP address of the router (or default gateway) on the local network segment the client should use to transmit to systems on other network segments
             • Domain Name Server
               • Specifies the IP addresses of the servers the client will use for DNS name resolution
             • Host Name
               • Specifies the DNS host name the client will use
             • Domain Name
               • Specifies the name of the DNS domain on which the system will reside
           • NOTE BOOTP
             • The Bootstrap Protocol (BOOTP) is the predecessor to DHCP. The two are largely compatible; the primary difference is that BOOTP allocates IP addresses permanently, and not by leasing them.

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