1. Network+ Guide to Networks, Fourth Edition
Chapter 11
In-Depth TCP/IP Networking

2. 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, 4e

3. 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, 4e

4. 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, 4e

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

6. 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, 4e

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

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

9. 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, 4e

10. 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, 4e

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

13. 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, 4e

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

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

16. 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, 4e

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

18. 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, 4e

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

20. 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, 4e

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

22. 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, 4e

23. 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, 4e

24. 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, 4e

25. 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, 4e

26. 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, 4e

27. 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, 4e

28. 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, 4e

29. 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, 4e

30. 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, 4e

31. 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, 4e

32. 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, 4e

33. 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, 4e

34. 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
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35. Dig (continued) Figure 11-11: Output of a simple dig command
Network+ Guide to Networks, 4e

36. 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, 4e

37. 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, 4e

38. 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, 4e

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

40. 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, 4e

41. 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, 4e

42. 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, 4e

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

44. Summary
Subnetting separates one network or segment into multiple, logically defined segments, or subnets
Bits in a subnet mask that equal 1 indicate that corresponding bits in an IP address contain network information
Bits in a subnet mask that equal 0 indicate that corresponding bits in an IP address contain host information
CIDR allows the creation of supernets, or subnets established by using bits that normally would be reserved for network class information
Network+ Guide to Networks, 4e

45. Summary (continued)
Gateways facilitate communication between different subnets
Every device on a TCP/IP-based network has a default gateway
NAT allows a network administrator to “hide” IP addresses assigned to nodes on a private network
ICS is a service that allows a network of computers to share a single Internet connection through an ICS host computer
Network+ Guide to Networks, 4e

46. Summary (continued)
SMTP is responsible for moving messages from one server to another over TCP/IP-based networks
POP is a mail retrieval protocol
IMAP4 allows users to store messages on the mail server, rather than always having to download them to the local machine
The netstat utility displays TCP/IP statistics and the state of current TCP/IP components and connections
Network+ Guide to Networks, 4e

47. Summary (continued)
The nslookup utility allows you to look up the DNS host name of a network node by specifying the node’s IP address, or vice versa
The traceroute utility useful for determining router or subnet connectivity problems
VoIP is the use of packet-switched TCP/IP-based networks to carry voice signals
Network+ Guide to Networks, 4e