Network+ Guide to Networks 5th Edition

Chapter 10 In-Depth TCP/IP Networking

Objectives
Understand methods of network design unique to TCP/IP networks, including subnetting, CIDR, and address translation Explain the differences between public and private TCP/IP 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

DESIGNING TCP/IP-BASED NETWORKS

Designing TCP/IP-Based Networks

TCP/IP protocol suite use
Public Internet connectivity Private connection data transmission

TCP/IP fundamentals
IP: routable protocol
Interfaces requires unique IP address Node may use multiple IP addresses

Two IP versions: IPv4 and IPv6

IPv4: older; more common

Designing TCP/IP-Based Networks (contd.)

IPv4 addresses
Four 8-bit octets
Binary or dotted decimal

Network host name assignment

Dynamic using DHCP Static

Network classes: A, B, C, D, E
Class D, E addresses reserved Nodes network class provides information about segment network node belongs to

Subnetting
Separates network
Multiple logically defined segments (subnets)
Geographic locations, departmental boundaries, technology types

Subnet traffic separated from other subnet traffic Reasons to separate traffic
Enhance security Improve performance Simplify troubleshooting

Classful Addressing in IPv4

Figure 4-8 IP addresses and their classes

First, simplest IPv4 addressing type Adheres to network class distinctions Recognizes Class A, B, C addresses

Classful Addressing in IPv4 (contd.)

Network information (network ID)
First 8 bits in Class A address First 16 bits in Class B address First 24 bits in a Class C address

Host information
Last 24 bits in Class A address Last 16 bits in Class B address Last 8 bits in Class C address

Classful Addressing in IPv4 (contd.)

Figure 10-1 Example IPv4 addresses with classful addressing

Classful Addressing in IPv4 (contd.)

Drawbacks
Fixed network ID size limits number of network hosts Difficult to separate traffic from various parts of a network

IPv4 Subnet Masks

Identifies how network subdivided Indicates where network information located Subnet mask bits
1: corresponding IPv4 address bits contain network information 0: corresponding IPv4 address bits contain host information

IPv4 Subnet Masks (contd.)

Class Subnet Mask in Binary Subnet Mask in Decimal # Network Bits CIDR Notation

A B

11111111 00000000 00000000 00000000 255 0 0 0 11111111 11111111 00000000 00000000 255 255 0 0

8 16

/8 /16

11111111 11111111 11111111 00000000 255 255 255 0

24

/24

Network class
Associated with subnet mask

IPv4 Subnet Masks (contd.)

Table 10-2 ANDing

ANDing
Combining bits
Bit value of 1 AND another bit value of 1 results in 1 Bit value of 0 AND any other bit results in 0

ANDing logic
1: true, 0: false

IPv4 Subnet Masks (contd.)

Figure 10-2 Example of calculating a hosts network ID

ANDing example
Addresss fourth octet
Any combination of 1s and 0s Results in network ID fourth octet of 0s

Reserved Addresses
Cannot be assigned to node network interface; used as subnet masks Network ID
Bits available for host information set to 0 Classful IPv4 addressing network ID ends with 0 octet Subnetting allows network ID with other decimal values in last octet(s)

Broadcast address
Octet(s) representing host information equal all 1s Decimal notation: 255 (for class C)

IPv4 Subnetting Techniques

Subnetting breaks classful IPv4 addressing rules
IP address bits representing host information change to represent network information
Reduce usable host addresses per subnet Hosts, subnets available after subnetting related to host information bits borrowed

Subnetting a Class C Address

Subnet Mask in Binary Subnet Mask in Decimal # Usable Addr CIDR Notation

11111111 11111111 11111111 10000000 255 255 255 128 11111111 11111111 11111111 11000000 255 255 255 192 11111111 11111111 11111111 11100000 255 255 255 224 11111111 11111111 11111111 11110000 255 255 255 240

254 62 30 14

/25 /26 /27 /28

11111111 11111111 11111111 11111000 255 255 255 248

11111111 11111111 11111111 11111100 255 255 255 252

6
2

/29
/30

Calculating IPv4 Subnets

Formula: # Usable Addresses = 2n 2
n: number of subnet mask bits that are zero

Example
Class C network
Network ID: 199.34.89.0 Want to divide into six subnets

Calculating IPv4 Subnets (contd.)

Table 10-5 Subnet information for six subnets in an example IPv4 Class C network

Calculating IPv4 Subnets (contd.)

Class A, Class B, and Class C networks
Can be subnetted
Each class has different number of host information bits usable for subnet information Varies depending on network class and the way subnetting is used

LAN subnetting
LANs devices interpret device subnetting information External routers
Need network portion of device IP address

Figure 10-3 A router connecting several subnets

CIDR (Classless Interdomain Routing)

Also called classless routing or supernetting Not exclusive of subnetting
Provides additional ways of arranging network and host information in an IP address Conventional network class distinctions do not exist

Example: subdividing Class C network into six subnets of 30 addressable hosts each Supernet
Subnet created by moving subnet boundary left

Subnet and Supernet Masks

Suppose you are starting with a class C address like 192.168.0.0/24 This would be a subnet:
Subnet Address: 192.168.0.0 / 26 Subnet Mask: 11111111 11111111 11111111 11000000 255 255 255 192

Usable address range: 192.168.0.1 - 192.168.0.62

This would be a supernet:

Subnet Address: 192.168.0.0 / 22 Subnet Mask: 11111111 11111111 11111100 00000000 255 255 252 0 Usable address range: 192.168.0.1 - 192.168.3.254

CIDR (contd.)

Figure 10-5 Calculating a hosts network ID on a supernetted network

Example: class C range of IPv4 addresses sharing network ID 199.34.89.0

Need to greatly increase number of default host addresses

CIDR (contd.)
CIDR notation (or slash notation)
Shorthand denoting subnet boundary position Form
Network ID followed by forward slash ( / ), followed by number of bits used for network portion of the address Like 147.144.51.0/24

Internet Gateways
Gateway
A device that connects two networks or subnets

Default gateway
Sends LAN traffic to other subnets, such as the Internet Usually a router

Network nodes
Have one default gateway address
Assigned manually or automatically (DHCP)

Internet Gateways (contd.)

Figure 10-6 The use of default gateways

Address Translation
Public network
Any user may access
Little or no restrictions

Private network
Access restricted
Clients, machines with proper credentials

Hiding IP addresses
Provides more flexibility in assigning addresses

NAT (Network Address Translation)

Gateway replaces clients private IP address with Internet-recognized IP address

Address Translation (contd.)

Reasons for using address translation
Overcome IPv4 address quantity limitations Add marginal security to private network when connected to public network Develop network addressing scheme

SNAT (Static Network Address Translation)

Client associated with one private IP address, one public IP address
Never changes

Useful when operating mail server

Address Translation (contd.)

Figure 10-7 SNAT (Static Network Address Translation)

Address Translation (contd.)

DNAT (Dynamic Network Address Translation)
Also called IP masquerading Internet-valid IP address might be assigned to any clients outgoing transmission

PAT (Port Address Translation)

Each client session with server on Internet assigned separate TCP port number
Client server request datagram contains port number

Internet server responds with datagrams destination address including same port number

Address Translation (contd.)

Figure 10-8 PAT (Port Address Translation)

Address Translation (contd.)

NAT
Separates private, public transmissions on TCP/IP network

Gateways conduct network translation

Most networks use router

Gateway might operate on network host

Windows operating systems
ICS (Internet Connection Sharing)

TCP/IP MAIL SERVICES

TCP/IP Mail Services

E-mail
Most frequently used Internet services Functions
Mail delivery, storage, pickup

Mail servers
Communicate with other mail servers Deliver messages, send, receive, store messages

Mail clients
Send messages to; retrieve messages from mail servers

SMTP (Simple Mail Transfer Protocol)

Used to send email
From one mail server to another

Operates at Application layer

Relies on TCP at Transport layer Uses TCP port 25

Email client software

Administrator must specify SMTP server name
Such as smtp.gmail.com

MIME (Multipurpose Internet Mail Extensions)

SMPT drawback: ASCII characters only MIME standard encodes, interprets binary files, images, video, non-ASCII character sets within email message
Identifies each mail message element according to content type
Text, graphics, audio, video, multipart

Does not replace SMTP

Works in conjunction with it

Encodes different content types

Fools SMTP

POP (Post Office Protocol)

Application layer protocol
Retrieve messages from mail server

POP3 (Post Office Protocol, version 3)

Current, popular version Relies on TCP, operates over port 110 Store-and-forward type of service

Advantages
Minimizes server resources
Mail deleted from server after retrieval Disadvantage for mobile users

Mail server, client applications support POP3

IMAP (Internet Message Access Protocol)

More sophisticated alternative to POP3 IMAP4: current version Advantages
Replace POP3 without having to change e-mail programs E-mail stays on server after retrieval
Good for mobile users

IMAP (contd.)
Features
Users can retrieve all or portion of mail message Users can review messages and delete them
While messages remain on server

Users can create sophisticated methods of organizing messages on server Users can share mailbox in central location

IMAP (contd.)
Disadvantages
Requires more storage space, processing resources than POP servers Network managers must watch user allocations closely If the IMAP4 server fails, users cannot access mail

ADDITIONAL TCP/IP UTILITIES

Additional TCP/IP Utilities

TCP/IP transmission process
Many points of failure
Increase with network size, distance

Utilities
Help track down most TCP/IP-related problems Help discover information about node, network

Nearly all TCP/IP utilities

Accessible from command prompt Syntax differs per operating system

Ipconfig
Command-line utility providing network adapter information
IP address, subnet mask, default gateway

Windows operating system tool

Command prompt window
Type ipconfig and press Enter

Switches manage TCP/IP settings

Forward slash ( / ) precedes command switches

Requires administrator rights

To change workstations IP configuration

IPCONFIG | MORE
Useful in Vista and Windows 7 Because they have a lot of extra virtual network adapters

Renewing a IP Address
IPCONFIG /RELEASE
Ends the current IP address lease

IPCONFIG /RENEW
Asks DHCP for a new IP address

These commands are often required when moving from one LAN to another

Ifconfig
Utility used on UNIX and Linux systems
Modify TCP/IP network interface settings, release and renew DHCP-assigned addresses, check TCP/IP setting status Runs at UNIX, Linux system starts
Establishes computer TCP/IP configuration

Used alone or with switches

Uses hyphen ( - ) before some switches No preceding character for other switches

Netstat
Displays TCP/IP statistics, component details, host connections Used without switches
Displays active TCP/IP connections on machine

Can be used with switches

-a shows all connections including listening ones -n display raw port numbers instead of letters like http

For help, use NETSTAT /?

Nbtstat
NetBIOS
Used on Windows LANs Protocol runs in Session and Transport layers Associates NetBIOS names with workstations Not routable
Can be made routable by encapsulation

Nbtstat utility
Provides information about NetBIOS statistics Resolves NetBIOS names to IP addresses
Limited use as TCP/IP diagnostic utility

Hostname, Host, and Nslookup

Hostname utility
Provides clients host name
Administrator may change

Nslookup
Query DNS database from any network computer
Find the device host name by specifying its IP address

Verify host configured correctly; troubleshoot DNS resolution problems

Nslookup

Dig
Domain information groper Similar to nslookup
Query DNS database Find specific IP address host name

Useful for diagnosing DNS problems Dig utility provides more detailed information than nslookup Flexible: two dozen switches Included with UNIX, Linux operating systems Windows system: must obtain third party code

Dig Example
Dig for Windows is at link Ch 10a

Whois
Query DNS registration database
Obtain domain information

Troubleshoot network problems Syntax on Linux or Unix

whois xxx.yy
xxx.yy is second-level domain name

Windows system
Requires additional utilities

Web sites provide simple, Web-based interfaces

Traceroute
Windows-based systems: tracert Linux systems: tracepath ICMP ECHO requests
Trace path from one networked node to another Identifying all intermediate hops between two nodes

Transmits UDP datagrams to specified destination

Using either IP address or host name
To identify destination

Command used a number of switches

Traceroute (contd.)

Mtr (my traceroute)

UNIX, Linux operating systems
Route discovery, analysis utility Combines ping, traceroute functions
Output: easy-to-read chart

Simplest form
mtr ip_address or mtr host_name
Run continuously Stop with Ctrl+C or add limiting option to command

Number of switches refine functioning, output Results misleading

If devices prevented from responding to ICMP traffic

Mtr (my traceroute)

Windows XP, Vista, Server 2003, Server 2008
Pathping program as command-line utility Similar switches as mtr Pathping output differs slightly
Displays path first Then issues hundreds of ICMP ECHO requests before revealing reply, packet loss statistics

Route
Route utility
Allows viewing of hosts routing table

UNIX or Linux system

Type route and press Enter

Windows-based system
Type route print and press Enter

Cisco-brand router
Type show ip route and press Enter

Route (contd.)

Figure 10-16 Example routing table

Route (contd.)

Table 10-6 Fields in routing table on a UNIX host

Route (contd.)
Route command
Add, delete, modify routes

Route command help

UNIX or Linux system
Type man route and press Enter

Windows system
Type route ? and press Enter