Network+ Guide to Networks,
Fourth Edition
Chapter 11
In-Depth TCP/IP Networking
Network+ Guide to Networks, 4e 2
Objectives
•
Understand methods of network design unique to
TCP/IP networks, including subnetting, CIDR, NAT
and ICS
•
Explain the differences between public and private
networks
•
Describe protocols used between mail clients and
mail servers, including SMTP, POP3, and IMAP4
•
Employ multiple TCP/IP utilities for network
discovery and troubleshooting
Network+ Guide to Networks, 4e 3
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
–

–
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 6
Classful Addressing (continued)
Figure 11-1: Example IP addresses with classful addressing
Network+ Guide to Networks, 4e 7
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 8
Subnet Masks (continued)

Subnetting Techniques (continued)
Table 11-4: Class C subnet masks
Network+ Guide to Networks, 4e 14
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 15
Calculating Subnets (continued)
Figure 11-3: A router connecting several subnets
Network+ Guide to Networks, 4e 16
Calculating Subnets (continued)
Figure 11-3 (continued): A router connecting several subnets
Network+ Guide to Networks, 4e 17
CIDR (Classless Interdomain Routing)
•
Classless routing or supernetting

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 20
Internet Gateways (continued)
Figure 11-6: The use of default gateways
Network+ Guide to Networks, 4e 21
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 22

–
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 25
TCP/IP Mail Services
•
E-mail 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