Chapter 11 In-Depth TCP/IP Networking

Designing TCP/IP-Based Networks Review of some TCP/IP fundamentals: IP is a routable protocol On a network using TCP/IP, each interface associated with unique IP address Some nodes may use multiple IP addresses IP addresses consist of four 8-bit octets Many networks assign IP addresses and host names dynamically, using DHCP Every IP address can be associated with a network class Network+ Guide to Networks, 4e2http://

Subnetting Separates network into multiple, logically defined segments (subnets) Each subnet’s traffic separated from every other subnet’s traffic Enhances security Subnetworks must be connected via routers or other Layer 3 devices Improves performance Data is selectively retransmitted Simplifies troubleshooting Network+ Guide to Networks, 4e3http://

Classful Addressing Adheres to network class distinctions Only Class A, B, and C addresses are recognized Network ID limited to first 8 bits in Class A, first 16 bits in Class B, and first 24 bits in Class C Fixed network ID size ultimately limits number of hosts a network can include Network+ Guide to Networks, 4e4http://

Classful Addressing (continued) Network+ Guide to Networks, 4e5 Figure 11-1: Example IP addresses with classful addressing

Subnet Masks Subnetting depends on subnet masks to identify how a network is subdivided Indicates where network information is located in an IP address “1” bits indicate corresponding bits in IP address contain network information “0” bits indicate corresponding bits in IP address contain host information To calculate host’s network ID given IP address and subnet mask, perform ANDing Network+ Guide to Networks, 4e6http://

Subnet Masks (continued) Network+ Guide to Networks, 4e7 Table 11-1: Default subnet masks

Subnet Masks (continued) Network+ Guide to Networks, 4e8 Figure 11-2: Example of calculating a host’s network ID Table 11-2: ANDing

Reserved Addresses Certain types of IP addresses reserved for special functions In network IDs, bits for host information set to 0 In broadcast addresses, octet(s) representing host information set to all 1s (255 in decimal notation) Network+ Guide to Networks, 4e9http://

Subnetting Techniques Subnetting breaks rules of classful addressing Some bits that in classful addressing would represent host information changed to represent network information Reduce number of usable host addresses per subnet Network+ Guide to Networks, 4e10http://

Subnetting Techniques (continued) Network+ Guide to Networks, 4e11 Table 11-3: Class B subnet masks

Subnetting Techniques (continued) Network+ Guide to Networks, 4e12 Table 11-4: Class C subnet masks

Calculating Subnets Formula for determining how to modify a default subnet mask: 2n-2=Y n = number of bits in subnet mask that must be switched from 0 to 1 Y = number of subnets that result Extended network prefix: Additional bits used for subnet information plus existing network ID Class A, B, and C networks can all be subnetted External routers pay attention to only the network portion of devices’ IP addresses Network+ Guide to Networks, 4e13http://

Calculating Subnets (continued) Network+ Guide to Networks, 4e14 Figure 11-3: A router connecting several subnets

Calculating Subnets (continued) Network+ Guide to Networks, 4e15 Figure 11-3 (continued): A router connecting several subnets

CIDR (Classless Interdomain Routing) Classless routing or supernetting Provides additional ways of arranging network and host information in an IP address Supernet: Subnet created by moving subnet boundary to the left Generates more usable IP addresses CIDR notation (slash notation): network ID followed by forward slash (/), followed by number of bits used for extended network prefix CIDR Block Network+ Guide to Networks, 4e16http://

CIDR (continued) Network+ Guide to Networks, 4e17 Figure 11-5: Calculating a host’s network ID on a supernetted network Figure 11-4: Subnet mask and supernet mask

Internet Gateways Combination of software and hardware enabling two different network segments to exchange data Every device on a TCP/IP-based network has a default gateway First interprets outbound requests to other subnets Interprets inbound requests from other subnets Each node on network has one default gateway May be network interface on a router Must maintain routing tables as well Core gateways make up the Internet backbone Network+ Guide to Networks, 4e18http://

Internet Gateways (continued) Network+ Guide to Networks, 4e19 Figure 11-6: The use of default gateways

NAT (Network Address Translation) Default gateways can be used to “hide” IP numbers assigned within an organization Clients behind gateway may use any IP addressing scheme Even non-legitimate schemes Must have legitimate IP address to exchange data with Internet NAT: when client’s transmission reaches default gateway, it assigns client’s transmission a valid IP address Network+ Guide to Networks, 4e20http://

NAT (continued) Network+ Guide to Networks, 4e21 Figure 11-7: NAT through an Internet gateway

ICS (Internet Connection Sharing) Computer with Internet access (ICS host) configured to translate requests to and from Internet on behalf of other computers on network Acts as DHCP server, DNS resolver, and NAT gateway for clients on its LAN Network adapter on ICS host assigned IP address of Clients must be set up to obtain IP addresses automatically ICS host assigns clients IP addresses in range of through Network+ Guide to Networks, 4e22http://

Intranets and Extranets Intranet: network or part of network that uses browser-based services to exchange information within an enterprise Used for supplying HTTP-accessible documents, , file sharing, document management, and collaboration Defined by its security policies Extranet: network that uses Internet-like services and protocols to exchange information within an organization and with certain, authorized users outside of that organization Network+ Guide to Networks, 4e23http://

TCP/IP Mail Services is most frequently used Internet service that network administrators manage Mail servers communicate with other mail servers to deliver messages across Internet Hundreds of software packages for mail servers exist Sendmail, Microsoft Exchange Server, Lotus Notes, Novell Groupwise Mail clients send/retrieve messages to/from mail servers Servers and clients communicate through TCP/IP Application layer protocols Network+ Guide to Networks, 4e24http://

SMTP (Simple Mail Transfer Protocol) Protocol responsible for moving messages between mail servers over TCP/IP-based networks Belongs to Application layer of TCP/IP Model Relies on TCP at Transport layer Operates from port 25 Relies on higher-level programs for instructions Can only transport or hold mail When configuring clients to use Internet , must identify user’s SMTP server Network+ Guide to Networks, 4e25http://

MIME (Multipurpose Internet Mail Extensions) Standard SMTP message format allows for lines that contain 1000 ASCII characters max Cannot handle pictures or formatted text MIME: standard for encoding and interpreting binary files, images, video, and non-ASCII character sets within messages Identifies each element of a message according to content type Works in conjunction with SMTP Network+ Guide to Networks, 4e26http://

POP (Post Office Protocol) Application layer protocol used to retrieve messages from mail servers POP3 is most current and commonly used version Mail delivered and stored on mail server until user connects (via client) to retrieve messages Mail deleted from server after retrieval Minimizes use of server resources Best suited to users who retrieve mail from same workstation all the time Network+ Guide to Networks, 4e27http://

IMAP (Internet Message Access Protocol) Developed as sophisticated alternative to POP3 IMAP4 is most current version Users can store messages on mail server IMAP4 provides the following features: Retrieve all or only a portion of any mail message Review messages and delete them while the messages remain on the server Create sophisticated methods of organizing messages on the server Share mailboxes in a central location Network+ Guide to Networks, 4e28http://

Additional TCP/IP Utilities TCP/IP comes with complete set of utilities that can help to track down most TCP/IP-related problems e.g., Ping, Telnet, ARP Nearly all TCP/IP utilities can be accessed from command prompt on any type of server or client running TCP/IP Syntax may differ depending on OS Options may differ according to OS Network+ Guide to Networks, 4e29http://

Netstat Displays TCP/IP statistics and details about TCP/IP components and connections on a host Port on which a particular TCP/IP service is running Network connections currently established Number of packets handled by network interface since activation Number of data errors Network+ Guide to Networks, 4e30http://

Netstat (continued) Common Netstat switches: -a lists all available TCP and UDP connections -e displays details about all packets that have been sent -n lists currently connected hosts according to their ports and IP addresses (in numerical form) -p allows you to specify what type of protocol statistics to list -r provides list of routing table information -s provides statistics about each packet transmitted by a host, separated according to protocol type Network+ Guide to Networks, 4e31http://

Nbtstat Given NetBIOS name, get IP address Common nbtstat switches: -a displays a machine’s name table given its NetBIOS name -A displays a machine’s name table given its IP address -r lists statistics about names that have been resolved to IP addresses by broadcast and by WINS -s displays a list of all the current NetBIOS sessions for a machine Network+ Guide to Networks, 4e32http://

Nslookup Query DNS database from any network computer and find host name of a device by specifying its IP address, or vice versa Provides host’s IP address, primary DNS server name, and address holding record for this name Many options (switches) Network+ Guide to Networks, 4e33http://

Dig Domain information groper (dig): similar to nslookup Provides more detailed information than nslookup e.g., specifics about resource records associated with host name Many switches Must be explicitly installed on Windows systems Network+ Guide to Networks, 4e34http://

Dig (continued) Network+ Guide to Networks, 4e35 Figure 11-11: Output of a simple dig command

Whois Query DNS registration database and obtain information about a domain Who is domain registered to? Technical person responsible for domain? Hosting entity? DNS Server addresses? Must install software to use on Windows systems Web-based alternatives exist e.g., Network+ Guide to Networks, 4e36http://

Traceroute (Tracert) Uses ICMP to trace path from one node to another Identifies all intermediate hops Useful for determining router or subnet connectivity problems Transmits series of UDP datagrams to specified destination Increases TTL as path is discovered Traceroute may stop before completing Device problem on path Device does not accept ICMP transmissions Often indicates firewall Network+ Guide to Networks, 4e37http://

Traceroute (continued) Common switches: -d instructs traceroute not to resolve IP addresses to host names -h specifies maximum number of hops packets should take when attempting to reach a host Default is 30 -w identifies timeout period for responses Network+ Guide to Networks, 4e38http://

Ipconfig TCP/IP administration utility for use with Windows NT, 2000, XP, and Server 2003 OSs Provides information about network adapter’s IP address, subnet mask, and default gateway Commonly used switches: /? displays list of available switches /all displays complete TCP/IP configuration information for each network interface on device /release releases DHCP-assigned addresses for all network interfaces /renew renews DHCP-assigned addresses for all network interfaces Network+ Guide to Networks, 4e39http://

Winipcfg Same as ipconfig utility, but applies to Windows 9x and Me OSs Graphical interface Network+ Guide to Networks, 4e40

Ifconfig TCP/IP configuration and management utility used on UNIX-type of systems Similar to ipconfig on Windows systems Commonly used switches: -a applies command to all interfaces on a device down marks interface as unavailable to network up reinitializes interface after it has been taken “down” Complete list of switches found in man pages Network+ Guide to Networks, 4e41http://

VoIP (Voice over IP) Use of packet-switched networks and TCP/IP to transmit voice conversations IP telephony Objectives for implementing VoIP: Lower costs for voice calls Supply new or enhanced features and applications Centralize voice and data network management Network+ Guide to Networks, 4e42http://

VoIP (continued) VoIP callers can use: Traditional telephone IP telephones: telephones designed for TCP/IP transmission Softphones: computers equipped with microphone, speaker, and VoIP client software IP telephones must have unique IP addresses More difficult to transmit voice signals over a packet- switched network than data signals Internet telephony: VoIP carried via Internet May also be carried over private lines Network+ Guide to Networks, 4e43http://

VoIP (continued) Network+ Guide to Networks, 4e44 Figure 11-16: Accessing a VoIP network from traditional telephones

VoIP (continued) Network+ Guide to Networks, 4e45 Figure 11-17: Accessing a VoIP network from IP phones