Bay Technical Associates RM356 User Manual
Reference Guide for the Model RM356 Modem Router
NETGEAR, Inc.
A Bay Networks Company
4401 Great America Parkway
Santa Clara, CA 95054 USA
Phone 800-211-2069
M-RM356NA-0
July 1998
© 1998 by NETGEAR, Inc. All rights reserved.
Trademarks
Bay Networks is a registered trademark of Bay Networ ks, Inc.
NETGEAR and Fir stGear are tr ademarks Bay Networks, Inc .
Microsoft, Windows, and Window s N T are registered trademarks of Microsoft Corporation.
Other bra nd and product names are registered trademarks or tradem arks of their respective holders.
Statement of Conditions
In the int erest of impr oving internal design, operational function, and/or reliability, NETGE A R reserves the right to
make changes to the product(s) described in this document without notice.
NETGEAR does not assume an y liability tha t m ay occur due to th e use or application of the product(s) or circu it
layout(s) described herein.
Federal Communications Commission (FCC) Compliance Notice: Radio Frequency Notice
This de vice complie s w ith part 15 of the FCC Rules. Operation is subject to the follow ing two condi tions:
• This dev ic e m a y no t cause harmfu l interfe r en ce.
• This device must accept any interference received, including interferen ce that may cause undesired operation.
Note: This equ ipment has been te sted and found to com ply with the limits for a Class B digital device, pursuant to
part 15 of th e F C C Rules. Thes e limits are designed to pr ov ide reaso nable pro tection against harm fu l in terfer en c e in a
residential installation. This equipment generates, uses, and can radiate radio frequency energy and, if not installed and
used in accordance with the instructions, may cause harmful interference to radio communications. H owever, there is n o
guarant ee tha t in te rf erenc e wil l no t oc cur in a pa rt ic ular ins ta llat io n. I f this equi pme nt do es ca use har mful in te rf erenc e to
radio or tele vision reception, which can be de termined by turning the equipment off and on, th e user is encouraged t o try
to correct the interference by one or more of the following measures:
• Reorient or relocate the receiving antenna.
• Increase the separation betwee n the equipment and receiver.
• Connect the equipm ent into an outl et on a circuit differe nt from that to which the receiver is connected.
• Consult the dealer or an experienced radio/TV technician for help.
EN 55 022 Declaration of Conformance
This is to certify that the Model RM356 Modem Router is shielded against the generation of radio interference in
accorda n ce with the application of Council Dire ctive 89 /336/EEC, Article 4a. Confor m ity is declared by the app lication
of EN 55 022 Class B (CISPR 22).
ii
Bestätigung des Herstellers/Importeurs
Es wird hiermit bestätigt, daß das Model RM356 Modem Router und Model gemäß der im BMPT-AmtsblVfg 243/1991
und Vfg 46/1992 aufgefü hrten Bestimmungen entstört ist. Das vorschri ftsmäßige Betreiben einiger Geräte (z.B.
Testsender) kann jedoch gewissen Beschränkungen unterliegen. Lesen Sie dazu bitte die Anm erkungen in der
Betrie bsanleitung.
Das Bundesamt für Zulassungen in der Telekommunikatio n w urde davon unterricht et, daß dieses G erät auf den Markt
gebrach t w urde und es ist berechtigt, die Serie auf die Erfüllung der Vorschriften hin zu überprüfen.
Certificate of the Manufacturer/Importer
It is hereby certified that the Model RM356 Modem Router has been sup pressed in accordance with the conditions set
out in the BMPT-AmtsblVf g 243/1991 and Vfg 46/1992. The operation of some equipment (for example, test
transmitters) i n accordance with the regulations m ay, however , be subject to certain restrictions. Plea se refer t o the notes
in the operating instructions.
Federal Office for Telecommunications Approvals has been notified of the placing of this equipment on the market
and has been granted the ri ght to test the series for co mpliance with the regula tions.
VCCI-2 Statement
This equi pment is in the 2nd Class category (infor m a tion equipment to be used in a residential area or an adjacent area
thereto) and conforms to the standards set by the Voluntary Contro l Council for Interference by Data Processing
Equipment and Electronic Office Machines aimed at preventing radio interferen ce in such residential areas.
When use d near a radio or TV receiver, it may become the cause of radio interference.
Read instructions for correct handling.
Customer Support
For assistance with installing and configuring your NETGEAR system or with post-installation questions or problems,
contact your point of purchase representative.
To contact customer support or to purchase additional copies of this document and publications for other NETGEAR
products, you can contact NETGEAR at the following numbers:
• Phone :
Australi a: 1800-142-046
France: 0800-90-2078
Germany: 0130-817305
Japan: 012 0-66-5402
Korea: 00308-11-0319
New Zealand: 0800-444-626
Sweden: 020-790086
United Kingdom: (44) 171-571-5120
U.S./Canada: 800-211-2069
•Fax:
U.S./Canada: 510-498-2609
iii
World Wide Web
NETGEAR maintains a World Wide Web Home Page that you can ac cess at the universal resource locator (URL)
http://NETGEAR.baynetworks.com . A direct connection to the In ternet and a Web browser such as Internet Explorer
or Netsca pe are required.
iv
Contents
Preface
Purpose ........................................................................................................................... xv
Audience ..........................................................................................................................xv
Conventions .....................................................................................................................xvi
Special Message Formats .........................................................................................xvi
Use of Enter, Type, and Press ...................................................................................xvi
Other Conventions ............. ......... .......... ......... .......... ......... .......... ......... .......... ......... .xvii
Related Publications .......................................................................................................xvii
Chapter 1
Introduction
About the Router ....................................................... ....... .. .......... ....... ....... .. .......... ....... .1-1
Features ..........................................................................................................................1-1
Key Featur e s ................... .......... ......... .......... ......... .......... ......... .......... ......... .......... ...1-2
V.90 Suppor t ............................................................................................................1-3
TCP/IP Support ........................................................................................................ 1-3
IP Address Masquerading by Dynamic NAT+ ....................................................1-3
Automatic Configuration of Attached PCs by DHCP ..........................................1-3
Security ....................................................................................................................1-4
Calling Line Identification ...................................................................................1-4
PAP and CHAP Authentication ..........................................................................1-4
Callback ............................................................................................................. 1-4
Management Support ..............................................................................................1-4
Basic Router Concepts ...................................................................................................1-5
What is a Router? ....................................................................................................1-5
Routing Information Protocol ....................................................................................1-5
IP Addresses and the Internet .................................................................................1-6
Netmask ...................................................................................................................1-8
Subnet Addressing ........................................................................ ....... .. .......... ....... .1-9
Contents v
Private IP Ad d r e sse s ............... ......... ......... .......... ......... ................... .......... ......... ....1-11
Single IP Address Opera tion Using NAT ................................................................1-12
Address Resolution Protocol ................... .......... ......... .......... ......... ......... .......... ......1-13
Domain Name Server .............................................................................................1 -13
IP Configuration by DHCP .....................................................................................1-14
Chapter 2
Router Installation and Connection
Package Contents ..........................................................................................................2-1
Checklists .......................................................................................................................2-2
Telephone Line Checklist .................................... ....... .. .......... ....... ....... .. .......... ....... .2-2
ISP Checkl i s t .......... ......... .......... ......... .......... ................... ......... .......... ......... .......... ...2-2
Single-User Account ..........................................................................................2-3
LAN Account .............................. .. ..... .. ..... ..... .. ..... ..... ..... .... ..... .. ..... .. ..... ..... .. ..... .2-3
Account Information ...........................................................................................2-3
Network Checklist ............................ ......... .......... ......... .......... ......... .......... ......... ......2-4
Connecting the Router ....................................................................................................2-5
Connecting the Serial Cable (Optional) .................................... ..... ....... ....... ....... ..... .2-7
Connecting to the Line Por t . .....................................................................................2-7
Connecting to the Hub Ports .. ..................................................................................2-8
Connecting a Telephone, Fax, or Modem .................................................................2-8
Connecting the Power Adapter ........................... ....... ....... ....... ..... ....... .. .......... ....... .2-8
Connecting for Configuration ..........................................................................................2-9
Connecting Through the Serial Port .........................................................................2-9
Connecting Through a Telnet Connection ................................................................2-9
Chapter 3
Router Configuration
Configuration Methods ................................................................................................... 3-1
Powering on the Router ..................................................................................................3-2
Navigating the Manager ............................................................... ....... ....... .. .......... ....... .3-3
Manager Menu Summary ...............................................................................................3-5
General Setup Menu ......................................................................................................3-6
MODEM Menus ..............................................................................................................3-7
MODEM Setup Menu ............................................................................................... 3-7
Advanced MODEM Setup Menu ..............................................................................3-8
vi Contents
Ethernet Menu ................................................................................................................3-9
General Setup Menu ................................................................................................3-9
DHCP and TCP/IP Setup ............................. ................... ......... ................... ...........3-10
Manager Password Setup .............................................................................................3 -12
Chapter 4
Configuration for Internet Access
Info rmat ion Checklist ..................... ......... ......... .......... ......... .......... ......... .......... ......... ......4-1
Internet Access Configuration ........................................................................................4-2
Configuration for Single-User Account ......................................... .. ....... ....... .......... .. ......4-3
Backup ISP Accounts .....................................................................................................4-4
Configuring for a Backup ISP ...................................................................................4-4
Switching to a Backup ISP .......................................................................................4-4
Chapter 5
Remote Node Configuration
Editing PPP Options .......................................................................................................5-4
Editing Script Options .....................................................................................................5-5
Chapter 6
Dial-In Configuration
Default Dial-In Setup .......................................................................................................6-1
Dial-In User Setup .......................................................................................................... 6-3
More On CLID ................... ......... .......... ......... .......... ......... .......... ......... ......... .......... ........6-5
Chapter 7
TCP/IP Configuration
LAN-to-LAN Application .................................................................................................. 7-1
Remote Node Setup ................... .......... ......... .......... ......... .......... ......... ......... .......... ........7-2
Static Route Setup ........................... ......... .......... ......... .......... ......... .......... ......... .......... ...7-4
Chapter 8
Filter Configuration
Router Filte r Structure .............. ......... .......... ......... .......... ......... .......... ......... .......... ......... .8-2
Configuring a Filter Set ................................................................................................... 8-2
Configuring a Filter Rule .................................................................................................8-4
TCP/IP Filter Rule ....................................................................................................8-4
Generic Filter Rule ...................................................................................................8-7
Contents vii
Applying a Filter Set .......................................................................................................8-8
Reducing Unnecessary Calls by Windows 95 ................................ ..... .. ..... .. ..... ..... .. ..... .8-9
Diagnosing the Situation .......................................................................................... 8-9
Implementing the Filter ...........................................................................................8-11
Applying the Filter ..................................................................................................8-14
Chapter 9
System Maintenance
System Statu s ................ .......... ......... .......... ......... .......... ......... .......... ......... .......... ......... .9-1
Terminal Baud Rate ........................................................................................................9-3
Log and Trace .................................................................................................................9-3
View Error Log .........................................................................................................9-4
Syslog and Accounting .............................................................................................9-4
Diagnostic Menu .............................................................................................................9-6
Call Testing and TCP/IP Tools .................................................................................. 9-7
System Tools ............... ......... .......... ......... .......... ......... .......... ......... ......... .......... ........9-8
Back Up Configuration ....................................................................................................9-9
Restore Confi g uration ................. .......... ......... .......... ......... .......... ......... ......... .......... ........9-9
Software Update .............................................................................................................9-9
Command Interpreter Mode .........................................................................................9-10
Call Control ...................................................................................................................9-10
Blacklist ..................................................................................................................9-11
Budget Management ..............................................................................................9-11
Call History .............................................................................................................9 -11
Chapter 10
Troubleshooting
Basic Functio n i n g .. ................... ......... .......... ......... .......... ......... .......... ......... .......... ........10-1
LEDS ...................................................................................................................... 10-1
LAN Link LED .........................................................................................................1 0-1
Troubleshooting a TCP/ IP Net wor k Usin g a Ping Utilit y ............................................. ..10-2
Testing the LAN Path to Your Router ......................................................................10-2
Testing the Path from Your PC to a Remote Device ...............................................10-3
Troubleshooting a Remote Node or ISP Connection .................................. .. .......... ......10-4
Troubleshooting a Remote User Connection ................................................ .......... .. ....10-4
viii Contents
Troubleshooting the Manager Interface ........................................................................ 1 0-5
Restoring the Default Configuration and Password ......................................................1 0-6
Using the Packet and Log Trace ...................................................................................1 0-7
Packet Trace Display Format ..................................................................................10-8
Appendix A
Technical Specifications
Index
Contents ix
x Contents
Figures
Figure 1-1. Three Main Address Classes ...................................................................1-7
Figure 1-2. Example of Subnetting a Class B Address ..............................................1-9
Figure 1-3. Single IP Address Operation Using NAT ................................................1 -12
Figure 2-1. Front Panel of the Model RM356 Modem Router ....................................2-5
Figure 2-2. Rear Panel of the Model RM356 Modem Router .....................................2-7
Figure 3-1. Start-up Display .......................................................................................3-2
Figure 3-2. Manager Main Menu ........................... .. ....... .......... ....... .. ....... .......... .. ......3-4
Figure 3-3. Menu 1 - General Setup ...........................................................................3-6
Figure 7-1. LAN-to- L AN Ap p li ca tion .................... ......... .......... ......... ......... .......... ........7-1
Figure 8-1. Outgoing Packet Filtering Process ...........................................................8-1
Figure 8-2. LAN Packet Which Triggered Last Call ....................................................8-9
Figure 8-3. Menu 21 Filter Set Configuration ...........................................................8-11
Figure 8-4. TCP/IP Filter Rule Menu ............................ ....... ....... ..... ....... .. .......... ......8-12
Figure 8-5. Filter Rules Summary Menu ................. ..... .. ..... ..... .. ..... .. ..... .. ..... ..... ..... .8-13
Figure 8-6. Remote Node Profile Menu ....................................................................8-14
Figure 9-1. Packe t Exa mples ...................... .......... ......... .......... ......... .......... ......... ......9-3
Figure 9-2. Trace Display for a Successful TCP/IP Protocol Connection ...................9-7
Figure 9-3. Trace Display for a Failed TCP/IP Protocol Connection ...........................9-8
Figure 10-1. Packet Trace Display Definitions ............................................................1 0-8
Figure 10-2. PPP Message Definitions ...................................................................... 1 0-8
Figures xi
xii Figures
Tables
Table 1-1. Netmask Notation Translation Table for One Octet ................................1 -10
Table 1-2. Netmask Formats ...................................................................................1-11
Table 2-1. LED Descriptions .....................................................................................2-6
Table 3-1. Manager Menu Commands ............................................................ .. ......3-3
Table 3-2. Manager Menu Summary .......................................................................3-5
Table 3-3. MODEM Setup Menu Parameters ...........................................................3-7
Table 3-4. Advanced MODEM Setup Menu Field Descriptions ...............................3-8
Table 3-5. Ethernet General Setup Menu Filter Sets ........................................ .. ......3-9
Table 3-6. Menu 3 - Ethernet Setup Menu Fields ..................................................3-10
Table 5-1. Menu 11.1 - Remote Node Profile Fields ................................................5-2
Table 5-2. Fields in Menu 11.2 - Remote Node PPP Options ..................................5-4
Table 5-3. Script Options Display ..............................................................................5-5
Table 6-1. Fields in Menu 13 - Default Dial-in Setup ................................................6-2
Table 6-2. Fields in Menu 14.1 - Edit Dial-in User ................................................... 6-4
Table 7-1. Fields in Menu 11.1 - Remote Node Profile Fields .................................7-2
Table 7-2. Menu 11.3 - Remote Node Network Layer Options Fields ...................... 7-3
Table 7-3. Edit IP Static Route Menu Fields ............................................................7-5
Table 8-1. Abbreviations Used in Menu 21.1 - Filter Rules Summary .....................8-3
Table 8-2. Abbreviations Used if Filter Type Is IP .....................................................8-3
Table 8-3. Abbreviations Used if Filter Type Is GEN .................................................8-4
Table 8-4. TCP/IP Filter Rule Menu Fields ............................ .. ..... ..... .... ..... ..... .. ..... .8-5
Table 8-5. Generic Filter Rule Menu Fields ................. .......... .. ....... ....... ..... ....... ......8-7
Tables xiii
Table 9-1. System Maintenance Status Menu Fields ................................................9-1
Table 9-2. System Maintenance Status Menu Fields ...............................................9-2
Table 9-3. System Maintenance - Log and Trace Menu Fields ........................... ......9-4
Table 9-4. System Maintenance - Syslog and Accounting Menu Fields ...................9-5
Table 9-5. System Maintenance - Diagnostic Menu Fields ..................................... 9-6
xiv Tables
Preface
Congratulation s on your purch ase of the NETGEAR™ Model RM356 Modem Router.
The Model RM356 Modem Router integrates a 4-port hub and one high-speed 56K internal
modem into a single package. In a modem-sized box, yo ur Model RM356 router o ffers a complete
internetwor king solution for your home or branch office. The Model RM356 router is ideal for
browsing the Internet, receiving calls from remote dial-in users, or making LAN-to-LAN
connections to remote nodes.
The Model RM356 rout er features one 56 kilobits per second (Kbps) modem line that can connect
directly to your local PSTN (Public Switc h Telephone Network) network, the reby saving you the
cost of buying additional external modems.
Purpose
This guide describes the featu res of the Model RM356 Modem Router and provides installation
and configur ation instructions.
Aud i en ce
To configure and install the Model RM356 Modem Router, you should have the following
background and experience:
• Working knowledge of basic network management concepts a nd term inology
• Working knowledge of tools and procedures for installing and operating sensiti ve electronic
equipment
Preface xv
Reference Guide for the Model RM356 Modem Router
Conventions
This section describes the conventions used in this guide.
Special Message Formats
This guide uses the following formats to highlight special messages:
This format is used to highlight inf ormation of importance or special interest.
Note:
Caution:
equipment failur e or loss of data.
Warning:
equipment damage.
Danger:
mishandling equipment.
This format is used to highlight information that will help you preve nt
This format is used to highlight information about the possibility of injury or
This format is used to alert you that you may incur an electrical shock by
Use of Enter, Type, and Press
This guide uses “enter,” “type,” and “press” to describe the following actions :
• When you read “enter,” type the text and press the Enter key.
• When you read “type,” type the text, but do not press the Enter key.
• When you read “press,” press only the alphanumeric or named key.
xvi Preface
Reference Guide for the Model RM356 Modem Router
Other Conventions
This guide uses the following typographical conventions:
italics
courie r fon t
Initial Caps Menu titles and window and button names.
[Enter] Named keys in text are shown enclosed in square brackets. The notation
[Ctrl]+C Two or more keys that must be pressed simultaneously are shown in text
ALL CAPS DOS file and directory names.
Book titles and UNIX file , command, and directory names.
Screen text, use r-typed command-line entries.
[Enter] is used for the Enter key and the Return key.
linked with a plus (+) sign.
Related Publications
For more information a bout configuring the Model RM356 Modem Router using FirstGear™
configuration software, refer to
Router
(part number M1-RM356NA-0).
For more in formati on about addr ess assig nment, re fer to RFC 1597,
Internets,
the Internet Engineer ing Task Force (IETF).
and RFC 1466,
Getting Started Using FirstGear for the Model RM356 Modem
Address Allocation for Private
Guidelines for Management of IP Address Space,
which are published by
For more information a bout IP addre ss translation, refer to RFC 1631,
Translator (NAT)
Preface xvii
.
The IP Network Addre ss
Chapter 1
Introduction
This chapter describ es the fe atures of the NETGEAR Model RM356 Modem Router and disc usses
planning considerations for installation.
About the Router
The Model RM356 Modem Router transports data from one local area network (LAN) to another
through a wide area network (WAN) connection.
The router compares the network addresses of data packets sent through the LAN to the entries in
its address tables. If a match is found for a destination network, the rou ter passes the packet to the
path indicated using the ent ry in the routing table. The entry in the path list contains the phone
number(s) of the target router. The router sends the number to the modem port to connect the call.
The WAN path is established, and the data is sent to the remote unit. At the receiving end, the
process operates in the reverse order, from the modem port to the LAN port.
The internal 56K modem in the Model RM356 router allows downstrea m data rates of up to
56 Kbps from your Internet service provider (ISP) and upstream rates of up to 33.6 Kbps.
Features
The Model RM356 Modem Router is a flexible, high-performance, easy-to-use router that
provides a cost-effective solution for i nte lligent networ king a ccess across an a nalog t elepho ne line.
With minimum setup, you c an ins tall and use the router within minutes to meet a wide variety of
networking requirements.
Introduction 1-1
Reference Guide for the Model RM356 Modem Router
Key Features
The Model RM356 Modem Router provides the following features:
• Internal high-speed analog modem
– V.90 standard 56K modem operation to provide up to 56 Kbps downstream data rate
from your ISP
• Dial-on-demand
– Calls automatically pla ced and terminated as needed without user interven tion
• Protocol Support
– IP routing
– Dynamic NAT+ for operation with a single static or dynamic IP address
– DHCP for dynamically assigning network configuration information to LAN
workstations
• Industry-sta ndard compression
– Hi/fn (Stac LZS) compression with CCP
• Easy installation a nd management
™
– FirstGear
graphical user interface (GUI) management software for Windows® user s
– Built-in Manage r int erface for Macintosh, UNIX, and PC users, accessible by terminal
or Telnet Protocol
– Configurable through the LAN—no serial connection required
• Security
– Password access control on manag ement functions
– Dial-in access contr ol by Calling Line Identification (CLID) and Callbac k
– PAP and CHAP authentication support
• Four-port twisted pai r Ether net hub
– Four RJ-45 interfaces for connection to 10BASE-T workstations
1-2 Introduction
Reference Guide for the Model RM356 Modem Router
• Eleven LEDs for easy monitoring of status and activity
• Flash EPROM for firmware upgrade
• Five-ye ar warranty
• Free technical support se ve n days a week, twe nty-four hours a day
V.90 Support
The Model RM356 router is designed to take advantage of the V.90 standard for transmission of
data over analog telephone networks.
One advantage of using a dial-up modem inter fac e to connect routers is that the connection is set
up only if data needs to be sent to the remote network. The router sets up a call, transfers the data,
then hangs up automatically whe n the conne ction is no longer needed.
TCP/IP Support
The Model RM356 router supports the T ransmission Control Protocol /Internet Protocol (TCP/IP)
and Routing Information Protoc ol (RIP).
For further information about TCP/IP, refer to “
IP Address Masquerading by Dynamic NAT+
The router allows an entire department of networked PCs to share an Internet account using only a
single IP address, whic h may be static ally or dyn amically as signed by your ISP. This techniq ue, an
extension of network addre ss translation (NAT), is known as IP address masquerading and
typically allows the use of a very inexpe nsive ISP account.
Automatic Configuration of Attached PCs by DHCP
The router can dynamically assig n network configuration information including IP, gateway, and
domain name server (DNS) addresses to attached PCs on the LAN using the Dynamic Host
Configuration Prot ocol (DHCP). This feature greatly simplifies c onfiguration of LAN-attached
workstations.
Introduction 1-3
Basic Router Concepts” on page 1-5.
Reference Guide for the Model RM356 Modem Router
Security
The Model RM356 Modem Route r is equippe d with se veral featur es design ed to mainta in sec urity.
These security featu res are described in this section.
Calling Line Identification
The use of Calling Line Ide ntification (CLID or Caller ID) ensures that incoming calling numbers
are checked against known numbers before a call is answered and access is gran ted , thus
providing a first leve l of security . I n many areas, you must specifically request that CLID
be e nabled by the telephone company for your line. In some regions, CLID may not be available.
PAP and CHAP Authentication
For connecting to other rout ers, the Model RM356 router supports two authentication protocols:
Password Authenticat ion Protocol (PAP) and Challenge Handshake Authentication Protocol
(CHAP). PAP sends the user name and password in plain text. CHAP scrambles the password
before it is sent over the wire. Although CHAP prov ides better security, PAP is readily availa ble
on more platfor ms .
Callback
For security and simplified cost accounting, the router implements Callback. When a remote user
dials in, the router can disconne ct the call a nd call the user ba ck so that any further call char ges are
incurred by the location of the router. The caller can provide the callback numb ers or, for security,
the router can be programmed to call back a predetermined number.
Management Support
The router is designed to be insta lled and made operational within minutes after connection to the
network.
If you are a PC user, the FirstGear software lets you easily configure the unit from the Windows
environment.
If you are a Macintosh, UNIX, or PC user, you can connect to the built-in Manager interface,
which can be accessed through a terminal connected to the Manager port or through a Telnet
session across the network. The built-in Manager interface manages and configures the
unit through an easily understood screen process.
1-4 Introduction
Reference Guide for the Model RM356 Modem Router
Basic Router Concepts
In general, the cost of providing network bandwidth is proportional to the data speed and the
distance over which the network ex te nds. Large amounts of bandwidth are provided easily a nd
relatively inexpe nsively in a local area network (office, department, and similar situations).
However, providing the same high data speeds between two local networks that are physically
distant may be prohibitive ly expensive. Because of this expense, high-spe ed local area networks
(LANs) are usually interconnected by slower-speed links to form a wide area network (WAN).
In order to make the best use of the slower WAN links, a mechanism must be in place at each
location for sele cting data meant onl y for anothe r loca tion and se nding it by th e best a vailable lin k.
The function of selecting and forwarding this data is performed by a router.
What is a Router?
A router is a device that forwards traffic between networks based on network layer information in
the data and on r outing tables maint ained by the router. In these routing tables, a router builds up a
logical picture of the overall network by gathering and exchanging information with other routers
in the network. Using this information, it chooses the best path for forwarding network traffic.
Routers vary in performanc e and scale , numb er of routing protocols supported, and types of
physical WAN connections supported. The Model RM356 Modem Router is a small office router
that routes the IP protocol over a dial-up telephone connection.
Routing Information Protocol
One of the proto cols used by a router to bu ild and maintain a picture of the network is the Rout ing
Information Protocol (RIP). RIP is a distance vector protocol, meaning that all the decisions about
which path to use are based upon a logical dist ance betwee n source and destin ation net works. This
distance is measured in “hops,” meaning the number of relaying routers in the path between the
source LAN router and the router of the destination LAN. For example, the LAN of router A is
considered to be 1 hop away. If router A can reach the network of router B by a direct WAN link to
the network of router B, the network of router B is two hops away. If another network must be
reached by calling router B and having router B forward the data, that network is n hops away,
where n is the number of routers traversed by the data to get to the network farthest away. When
there are multipl e paths to a ne twork, t he path with t he fe west hops i s chose n and is re garded a s the
best path, and all other information about how to get to that network is discarded.
Introduction 1-5
Reference Guide for the Model RM356 Modem Router
Using RIP, routers update one another periodically and check to see if there are any changes to be
added to the routing table. An important consideration is the convergence time, or how long it
takes for a change to the routing topology (such as a new node or a node failure) to be propagated
throughout the entir e RIP environm ent. To prevent this convergence process from being
excessively long, RIP is limited to 15 hops maximum.
The Model RM356 Modem Router supports both the older RIP-1 and the newer RIP-2 protocols.
Among other improvements, RIP-2 suppor ts subnetting and multicasting.
IP Addresses and the Internet
Because TCP/IP networks are interconnected widely across the world, every machine on the
Internet must have a unique address to make sure that transmitted data reaches the correct
destination. Blocks of addresses are assigned to organizations by the Internet Assigned Numbers
Authority (IANA) . Indi vidual u sers and small or ganizati ons may obtain their addres ses e ither f rom
the IANA or from an Internet service provider (ISP).
The Internet Protocol (IP) use s a 32-bit address structure. The address is usually written in dot
notation (also called dotted-decimal notation), in which each group of eight bits is written in
decimal form, separated by decimal points. For example, the binary address:
11000011 00100010 00001100 00000111
is normally written as:
195.34.12.7
which is easier to remember and easier to enter into your computer.
In addition, the 32 bits of the address are subdivided into two parts. The first part of the address
identifies the networ k, and the second part identifies the host node or station on the network. The
dividing point may vary dependi ng on the address r an ge and the application.
1-6 Introduction
Reference Guide for the Model RM356 Modem Router
There are five standard classes of IP addresses. These address classes have different ways of
determining the network and host sections of the address, allowing for different numbers of hosts
on a network. Each address type begins with a uniqu e bit pattern, which is used by the TCP/IP
software to identify the address class. After the address class has been determined, the software
can correctly identi fy the host section of the addres s. The three main address classes are illustrated
in Figure 1-1
Class A
Network Node
Class B
Class C
, which shows the network and host sections of the address f or each address type.
Network Node
Network Node
7261
Figure 1-1. Three Main Address Classes
Class A addresses can have up to 16,777,214 hosts on a single network. They use an 8-bit network
number and a 24-bit node number. Class A addresses are in this range:
1.x.x. x to 12 6. x. x.x.
Class B addresses can have up to 65,354 hosts on a network. A Class B address uses a 16-bit
network number and a 16-bit node number. Class B addresses are in this range :
128.1.x.x to 191.254.x.x.
Class C addresses can have 254 hosts on a network. Class C addr esses use 24 bits for the network
address and 8 bits for the node. They are in this range:
192.0.1.x to 223.255.254.x.
Class D addresses are used for multicasts (messages sent to many hosts). Class D addresses are in
this range:
224.0.0.0 to 239.255.255.255.
Introduction 1-7
Reference Guide for the Model RM356 Modem Router
Class E addresses are for experimental use.
This addressing structure allows IP to uniquely identify each physica l net work and each node on
each physical network.
For each unique value of the network portion of the address, the base address of the range (host
address of all zeros) is known as the network address and is not usually assigned to a host. Also,
the top address of the range (host address of all ones) is not assigned but is used as the broadcast
address for sending a packet simult aneously to all hosts with the same network address.
Netmask
In each of the above address classes, the size of the two parts (network address and host address)
is implied by the class. This partitioning scheme can also be expressed by a netmask assoc iated
with the IP address . A netmask i s a 32-bit qua ntity tha t, when l ogical ly ANDed with an I P address,
yields the network address. For instance, the netmasks for Class A, B, and C addresses are
255.0.0.0, 255.255.0.0, and 255.255.255.0, respectively.
For example, the address 192.168.170.237 is a Class C IP address whose network portion is the
upper 24 bits. When ANDed with the Clas s C netmask, as sh own here, onl y the network porti on of
the address remains:
11000000 10101000 10101010 11101101 (192.168.170.237)
ANDed with:
11111111 11111111 11111111 00000000 (255.255.255.0)
Equals:
11000000 10101000 10101010 00000000 (192.168.170.0)
As a shorter alte rnative to dotted-decimal notation, the netmask may also be expressed in terms of
the number of ones fr om the left. This n umber is appe nded to the IP addre ss, fol lowing a ba ckward
slash ( / ), as “/n.” In the example, the addre ss coul d be written as 192.168.170.237/24, indica ting
that the netmask is 24 ones followed by 8 zeros.
1-8 Introduction
Reference Guide for the Model RM356 Modem Router
Subnet Addressing
By looking at the addressing struc tures, you can see that even with a Class C address, there are a
large number of hosts per networ k. Such a st ructure is a n inefficient use of addresses if each end of
a routed link r equires a dif fer ent networ k number. It is unlikely that the small er of fice LANs wo uld
have that many devices. You can resolve this problem by using a technique known as subnet
addressing.
Subnet addressing allows us to split one IP network address into smaller multiple physical
networks known as subnetworks. Some of the node numbers are used as a subnet number instead.
A Class B address gives you 16 bits of node numbers translating to about 64,000 nodes. Most
organizat ions do not use 64,000 nodes, so there are free bits that can be reassigne d. Sub net
addressing makes use of those bits tha t are free , as illus trat ed in Figure 1-2
Class B
Network Subnet Node
7262
Figure 1-2. Example of Subnetting a Class B Address
.
A Class B address can be effectively translated into multiple Class C addresses. For example, the
IP address of 172. 16.0.0 is assigned, but node addresses are limited to 255 maximum, allowing
8 extra bits to use as a subnet address. The IP address of 172.16.97.235 would be interpreted as
IP network address 172.16, subnet number 97, and node number 235. In addition to extending
the number of addresses available, subnet addressing provides other benefits. Subnet addressing
allows a network manager to construct an address scheme for the network by using different
subnets for other geographical locations in the network or for other departments in the
organization.
Although the preceding exampl e uses the entire third octet for a subnet address, note that you are
not restricted to oct et bound aries in subnetting. To create more network numbers, you need only
shift some bits from the host address to the network address. For instance, to partition a Class C
network number (192.68.135.0) into two, you shift 1 bit from the host address to the network
address. The new netmask (or subnet mask) is 255.255.255.128. The first subnet has network
number 192.68.135.0 with hosts 192.68.135.1 to 129.68.135.126, and the sec ond subnet has
network number 192.68.135.128 with hosts 192.68.135.129 to 192.68.135.254.
Introduction 1-9
Reference Guide for the Model RM356 Modem Router
Note:
The number 192.68.135.127 is not assigned because it is the broadcast address
of the first subnet. And 192.68.135. 128 is not assigne d because it is the networ k address
of the second subnet.
Table 1-1 lists the additional subnet mask bits in dotted-decimal notation. To use the table, write
down the original c lass netm ask and re place t he 0 value octe ts wi th the dot ted-decimal v alu e of the
additional subnet bits. For instance, to partition your Class C network 204.247.203.0 with subnet
mask 255.255.255.0 into 16 subnets (4 bits), the new subnet mask becomes 255.255.255.240.
Table 1-1. Netmask Notation Translation Table for One Octet
Number of Bits Dotted-Decimal Value
1128
2192
3224
4240
5248
6252
7254
8255
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Reference Guide for the Model RM356 Modem Router
Table 1-2 displays several common netmask values in both the dotted-decimal and the
mask-length formats.
Table 1-2. Netmask Formats
Dotted-Decimal Mask-length
255.0.0.0 /8
255.255.0.0 /16
255.255.255.0 /24
255.255.255.128 /25
255.255.255.192 /26
255.255.255.224 /27
255.255.255.240 /28
255.255.255.248 /29
255.255.255.252 /30
255.255.255.254 /31
255.255.255.255 /32
NETGEAR strongly advises that all hosts on a LAN segment use the same netmask fo r the
following reasons:
• So that hosts recognize local IP broadcast packets
When a device broadcasts to its segment neigh bors, it uses a destination address of the local
network address wi th all ones for the host address. I n orde r for this scheme to wor k, a ll device s
on the segment must agree on which bits comprise the host address.
• So that a local router or bridge will know which addresses are local and which are remote
Private IP Addresses
If your networks are isolate d from the In ternet (for example, only between your two branch
offices), you can assign any IP addresses to the hosts without problems. However, the IANA has
reserved the following three blocks of IP addresses specifically for private networks:
10.0.0.0 - 10.255.255.255
172.16.0.0 - 172.31.255.255
192.16 8. 0. 0 - 192 .168.2 55 .2 55
NETGEAR recommends that you choose your private network number from this list.
Introduction 1-11
Reference Guide for the Model RM356 Modem Router
Regardless of your partic ular situation, do not create an arbitrary I P address; always follow the
guidelines explained here. For more information about address assignment, refer to RFC 1597,
Address Allocation for Private Internets,
Address Spac e
.
and RFC 1466,
Guidelines for Management of IP
Single IP Address Operation Using NAT
If multiple stations on a LAN need to access the Internet simultaneously, they usually have to
obtain a range of IP address es from the ISP. This type of Inte rnet ac count is much more co stly than
a single-addre ss acco unt t ypically us ed by a sing le use r with a t ermi nal adap ter ra ther tha n a r outer.
The Model RM356 Modem Router employs a method called extende d NAT. This method allows
an entire d epartment of networked P Cs to share an Inter net account using only a single IP address,
which may be statically or dynamica lly a ssigned by your ISP.
The router accomplishes this address sharing by translating the int erna l LAN IP addresses to a
single address that is globally unique on the Internet. The in ternal LAN IP addresses can be either
private addresses or registered addresses. For more inform ation about IP address translation, r efer
to RFC 1631,
The IP Network Address Translator (NAT)
.
Figure 1-3
illustrates a singl e IP address ope ration.
Private IP addresses
assigned by user
IP addresses
192.168.0.2
192.168.0.3
192.168.0.4
192.168.0.5
Figure 1-3. Single IP Address Operation Using NAT
1-12 Introduction
192.168.0.1 172.21.15.105
assigned by ISP
Internet
7786EA
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