Waters Network Systems GSM 2124 User manual

12
OPERATING MANUAL
GSM2116 and GSM 2124
Managed Switch with either 16 or 24 10/100/1000Base-TX ports
Plus two slots for 1000Base-SX or LX fiber
CORPORATE HEADQUATERS MANUFACTURING/CUSTOMER SERVICE
5001 American Blvd. W., Suite 605 945 37th Avenue, NW
Bloomington, MN 55437 Rochester, MN 55901
Phone: [phone] Phone: [phone]
Phone: [phone] Phone: [phone]
Fax: [phone] Fax: [phone]
Web site: http://www.watersnet.com

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TABLE OF CONTENTS
1.0 SPECIFICATIONS ...........................................................................................................................4
2.0 PACKAGE CONTENTS...................................................................................................................6
3.0 INTRODUCTION..............................................................................................................................6
3.1 HARDWARE FEATURES...........................................................................................................6
3.2 SOFTWARE FEATURES...........................................................................................................7
3.3 HARDWARE DESCRIPTION......................................................................................................8
3.4 REAR PANEL .........................................................................................................................9
3.5 OPTIONAL SFPMODULES......................................................................................................9
3.6 INSTALLATION......................................................................................................................10
3.7 OPTIONAL SFPMODULES....................................................................................................10
3.8 POWER ON.........................................................................................................................10
3.9 SWITCH TOPOLOGY.............................................................................................................10
4.0 NETWORK APPLICATIONS.........................................................................................................13
4.1 USING THE RS-232 SERIAL PORT CONNECTION ...................................................................13
4.2 CONFIGURING IP, SUBNET MASK AND DEFAULT GATEWAY.....................................................14
4.3 CONFIGURING THE SWITCH VIA THE WEB..............................................................................15
4.4 IPADDRESS ASSIGNMENT....................................................................................................16
5.0 WEB BASED MANAGEMENT......................................................................................................21
5.1 OVERVIEW OF WEB MANAGEMENT.......................................................................................22
5.2 SYSTEM INFORMATION.........................................................................................................25
5.3 IPCONFIGURATION..............................................................................................................26
5.4 TIME CONFIGURATION..........................................................................................................28
5.5 ACCOUNT CONFIGURATION ..................................................................................................30
5.6 MANAGEMENT POLICY.........................................................................................................31
5.7 VIRTUAL STACK ...................................................................................................................33
5.8 PORT CONFIGURATION ........................................................................................................35
5.8.1 PORT STATUS......................................................................................................................35
5.8.2 PORT CONFIGURATION ........................................................................................................38
5.8.3 SIMPLE COUNTER................................................................................................................39
5.8.4 DETAIL COUNTER ................................................................................................................40
5.9 MIRROR CONFIGURATION.....................................................................................................43
5.10 BANDWIDTH MANAGEMENT ..................................................................................................44
5.11 QOS(QUALITY OF SERVICE)CONFIGURATION ......................................................................45
5.12 SNMPCONFIGURATION.......................................................................................................51
5.13 IGMPSNOOPING ................................................................................................................53
5.14 MAXIMUM PACKET LENGTH ..................................................................................................55
5.15 DHCPBOOT.......................................................................................................................55
5.16 VLANS...............................................................................................................................56
5.16.1 VLAN MODE ..................................................................................................................56
5.16.2 TAG-BASED GROUP.........................................................................................................58
5.16.3 PORT-BASED GROUP .....................................................................................................60
5.16.4 TAG RULE.......................................................................................................................62
5.17 MACTABLE .......................................................................................................................63
5.18 GVRPCONFIGURATION......................................................................................................70
5.19 SPANNING TREE CONFIGURATION (STP) CONFIGURATION.....................................................74
5.19.1 STPSTATUS...................................................................................................................74
5.19.2 STPCONFIGURATION......................................................................................................76
5.19.3 STPPORT CONFIGURATION ............................................................................................77
5.20 TRUNKING CONFIGURATION.................................................................................................79

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5.21 802.1X CONFIGURATION.....................................................................................................84
5.22 ALARM CONFIGURATION ......................................................................................................93
5.23 CONFIGURATION..................................................................................................................95
5.23.1 SAVE/RESTORE ..............................................................................................................96
5.23.2 CONFIGURATION FILE......................................................................................................98
5.24 DIAGNOSTICS......................................................................................................................99
5.25 TFTPSERVER ..................................................................................................................101
5.26 LOG DATA .........................................................................................................................102
5.27 FIRMWARE UPGRADE.........................................................................................................103
5.28 REBOOT............................................................................................................................104
5.29 LOGOUT............................................................................................................................105
6.0 OPERATION OF CLI MANAGEMENT........................................................................................106
6.1 LOGIN...............................................................................................................................106
6.2 COMMANDS OF CLI ...........................................................................................................107
7.0 MAINTENANCE...........................................................................................................................127
7.1 EXAMPLES ........................................................................................................................127
8.0 TROUBLESHOOTING.................................................................................................................128
8.1 BEFORE CALLING FOR ASSISTANCE....................................................................................128
8.2 RETURN MATERIAL AUTHORIZATION (RMA) PROCEDURE.....................................................129
8.3 SHIPPING AND PACKAGING INFORMATION............................................................................129
9.0 WARRANTY ................................................................................................................................131

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1.0 Specifications
OPERATIONAL CHARACTERISTICS
MAC Address Table: 8K
Switching Mode: Store-and-forward
Memory Buffer Size:
GSM2116: 272KB
GSM2124: 400KB
Jumbo frame support
PERFORMANCE
Non-blocking wire speed
Auto negotiation
Auto-MDIX
Back pressure flow control for half duplex
Flow control for full duplex
MANAGEMENT FUNCTIONS
Web-based, SNMP (v1, v2c), CLI, or Telnet
Port setting for duplex and speed
Port trunking ( groups)
Port based and tagged VLANs (up to 256)
IGMP snooping
802.1x access control
GVRP/GARP
Port mirroring
Broadcast storm suppression
QoS
LACP
STP/RSTP
Enterprise MIB
RMON
NETWORK STANDARDS
IEEE 802.3
IEEE 802.3u
IEEE 802.3ab
IEEE 802.3z
IEEE 802.3x
IEEE 802.1q
IEEE 802.1p
IEEE 802.1d/w
IEEE 802.1x
IEEE 802.3ad

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EMI/SAFETY COMPLIANCE
FCC Part 15 Class A & CE Mark Approval
NETWORK CABLE CONNECTORS
RJ45 shielded female ports
10/100Mbps: CAT5 UTP or better
MM or SM with LC connectors
POWER SUPPLY
Internal power supply
Input Voltage
100 to 240 VAC, 50 to 60Hz
Power Consumption
30 watts maximum
OPERATING ENVIRONMENT
Ambient Temperature:
32° to 122°F (0° to 50°C)
Ambient Humidity (All Models except for GS2108):
5% to 90% (non-condensing)
MECHANICAL
Enclosure: Rack mountable
Cooling Method: Fan cooled
PHYSICAL CHARACTERISTICS
Dimensions: 8.23 x 17.40 x 1.73 in (209 x 442 x 44mm)
Weight: 9.26lbs (.2kg)
WARRANTY:
Limited Lifetime

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2.0 Package Contents
Examine the shipping container for obvious damage prior to installing this product. Notify the
carrier of any damage that you believe occurred during shipment. Ensure that the items listed
below are included. If an item is missing, please contact your supplier.
16 or 24 port 10/100/1000 Ethernet switch
Modules (optional)
Mounting Accessory for (19” rack shelf)
User’s manual
AC power cord
RS-232 Cable
3.0 Introduction
This user’s guide covers both the GSM2116 and the GSM2124 Waters’ managed switch. Both
switches meet IEEE802.3/u/x/z specifications. The switch has either sixteen or twenty-four
10/100/1000Mbps ports and two SFP fiber slots. The switch can be managed through RS-232
serial port via direct connection or through an Ethernet port using CLI or Web-based
management unit, associated with SNMP agent. With the SNMP agent, the network
administrator can logon the switch to monitor, configure and control each port’s activity through
easy to use menu options. The switch features comprehensive and useful functions such as
QoS (Quality of Service), Spanning Tree, VLAN, Port Trunking, Bandwidth Control, Port Security,
SNMP/RMON, IGMP Snooping capability via the intelligent software. The switch is suitable for
both metro-LAN and office application.
Note: Pictures in this user’s guide illustrate the 16 port model. The material in the user’s guide
applies to both the GSM2116 and the GSM2124.
Ports 15/23 and 16/24 provide two types of media --- copper and fiber. These ports support
either 10/100/1000Base-TX or 1000Base-SX auto-detected function.
For upgrading firmware, please refer to Section 5.27 for more details. The switch will not stop
operating while upgrading firmware and upon completion, the configuration is unchanged.
3.1 Hardware Features
The GSM switch provides the comprehensive features listed below for users to perform network
administration functions efficiently and provide maximum network security.
Conforms to IEEE 802.3, 802.3u, 802.3x, and 802.3ab and 802.3z
Sixteen or twenty-four auto sensing 10/100/1000 ports
Two 10/100/1000Mbps TP or 1000Mbps SFP Fiber dual media auto sense
144KB on-chip frame buffer
Maximum useable ports is 16
Jumbo frame support
Programmable classifier for QoS (Layer 4/Multimedia)
8K MAC address and 4K VLAN support (IEEE802.1Q)
Per-port shaping, policing, and broadcast storm control

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IEEE802.1Q-in-Q nested VLAN support
Full-duplex flow control (IEEE802.3x) and half-duplex backpressure
Supports online plug/unplug of SFP modules
Extensive front-panel diagnostic LEDs; System: Power, TP Ports 1-16 or 1-24: LINK/ACT,
10/100/1000Mbps, SFP Port 15 and 16 (or 23 and 24) SFP(LINK/ACT)
3.2 Software Features
The following lists management highlights of the GSM switch:
Supports per port traffic monitoring counters
Provides the status of each port and allows for port configuration
Supports per port traffic monitoring counters
Supports a snapshot of the system information upon login
Supports static trunk function
Supports 802.1Q VLAN
Three user login
Maximum packet length can be up to 9216 bytes for jumbo frame application
Supports DHCP broadcasting suppression
Supports on-line plug/unplug SFP modules
Supports QoS for real time applications based on the information taken from layer 2 to layer
4 such as VoIP
Supports port mirror function with ingress traffic
Supports rapid spanning tree
Supports 802.1x port security
SNMP access can be disabled to prevent illegal SNMP access
Trap event and alarm message can be transferred via email and mobile phone short
message
Supports external loopback test to verify if link is okay
Supports network time synchronization and daylight saving
Supports 120 event log records in the main memory and display on the local console

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3.3 Hardware Description
There are sixteen 10/100/1000 copper and two SFP fiber ports for optional removable modules
on the front panel of the switch. The LEDs, located on the left side of the front panel, contains a
power LED indicating the power status and the status of the eight working ports on the switch.
Figure 3.1 - GSM-2116 Switch
Figure 3.2 - Front view of GSM-2116 switch
Power Indication LED Fiber Port Status Indication LEDs
TP Port Status LEDs SFP Fiber Ports
RESET Button:
RESET button is used to reset the
management system.
Gi
g
abit Ethernet Port

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The following table provides the status and description of the LEDs:
LED Color Function
System LED
POWER Green Lit when +5V DC power is on and good
CPU LED Green Blinks when CPU is active
10/100/1000Ethernet TP Port 1 to 16 or 1 to 24 LED
LINK/ACT Green Lit when connection with remote device is good
Blinks when any traffic is present
Off when cable connection is not good
10/100/1000Mbps Green/ Amber
Lit green when 1000Mbps speed is active
Lit amber when 100Mbps speed is active
Off when 10Mbps speed is active
1000SX/LX Gigabit Fiber Port 15, 16 or 23, 24 LED
SFP(LINK/ACT) Green Lit when connection with the remote device is good
Blinks when any traffic is present
Off when module connection is not good
Table 3-1
3.4 Rear Panel
Located on the rear panel is the RS-232 DB-9 interface which is used for switch management
configuration.
3.5 Optional SFP Modules
If the SFP modules are installed, ports 15 and 16 (ports 23 and 24) can no longer be used for
10/100/1000 copper connection. The following lists the SFP modules that are available for the
GSM2116 switch:
SFP-1000SX-LC – multimode fiber transceiver with LC connector
SFP-1000LX-LC-10 – singlemode (10km) fiber transceiver with LC connector
SFP-1000LX-LC-30 – singlemode (30km) fiber transceiver with LC connector
Figure 3.3 - Rear View of GSM-2116
RS-232 DB-9 Connector
AC Line 100-240V 50/60 Hz

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3.6 Installation
Choose a surface for your switch that is clean, smooth and near a power outlet. Make sure that
there is enough clearance around the switch to allow attachment of cables, power cord and air
circulation.
1. Plug in the power cord into the switch.
2. Install the proper cable for network connection.
3. Plug the power cord into the power source.
3.7 Optional SFP Modules
The SFP modules are hot swappable, so you can plug or unplug the modules before and after
the switch is turned on. If you are installing the optional SFP fiber transceivers, follow these
guidelines:
1. Verify that the SFP module is the correct module and conforms to the chassis.
2. Slide the module along the slot.
3. Seat the module against the slot socket/connector.
4. Install the proper cable for network connection.
3.8 Power On
Once the switch is on, the bootloader loads the firmware into the memory. It will take about 30
seconds. Once the firmware is loaded, the switch will flash all of the LEDs once and
automatically perform a self test.
3.9 Switch Topology
Theoretically, the switch partitions the collision domain for each port so you may link switches
without limitations. However, network extension (cascading levels & overall diameter) must
follow IEEE 802.3/802.3u/802.3z and other 802.1 series protocol specifications, in which the
limitations are the timing requirement from physical signals defined by 802.3 series specification
of Media Access Control (MAC) and PHY, and layer 2 protocols such as 802.1d, 802.1q, and
LACP.

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The following table describes the cable and devices’ bit-time delay (round trip):
1000Base-X TP, Fiber 100Base-TX TP 100Base-FX Fiber
Round trip Delay: 4096 Round trip Delay: 512
CAT5 11.12/m CAT5 1.12/m Fiber Cable: 1.0/m
Fiber 10.10/m TP to fiber converter: 56
Bit time unit: 1ns (1sec./1000 Mega bit) Bit time unit: 0.01μs (1sec./100 Mega bit)
Table 3-2
Sum up all elements’ bit-time delay and the overall bit-time delay of wires/devices must be
within Round Trip Delay (bit times) in a half-duplex network segment (collision domain). This will
not be applied for full duplex operation. You may use the TP-Fiber module to extend the TP
node distance over fiber optic and provide the long haul connection.
A hierarchical network with minimum levels of switching may reduce the timing delay between
server and client station. Basically, with this approach, it will minimize the number of switches in
any one path; will lower the possibility of network loop and will improve network efficiency. If
more than two switches are connected in the same network, select one switch as Level 1 switch
and connect all other switches to it at Level 2. It is recommended to connect the Server/Host to
the Level 1 switch. This generally applies if no VLAN or other special requirements are applied.
Example 1: All switch ports are in the same local area network. All ports can access
each other (See Figure 3-4).
If VLAN is enabled and configured, each node in the network that can communicate with each
other directly is contained in the same VLAN area.
In Example 2, the VLAN area is defined by the configured VLAN. The switch supports both port-
based VLAN and tag-based VLAN. They are different in practical deployment, especially in
physical locations. The following diagram shows how the VLAN works.
Example 2a: Port-based VLAN (See Figure 3-5).
Fi
g
ure 3.4 - No VLAN Confi
g
uration Dia
g
ram

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1. As a member of a VLAN, you cannot be a member of a VLAN in another switch.
2. As a member of a VLAN, you cannot access a member of another VLAN.
3. The switch manager has to assign different names for each VLAN group
at one switch.
Case 2b: Port-based VLAN (See Figure 3.6).
This is an example of how VLANs can be set up between two switches.
1. VLAN1 members cannot access VLAN2, VLAN3 and VLAN4 members.
2. VLAN2 members cannot access VLAN1 and VLAN3 members, but they can access VLAN4
members.
3. VLAN3 members cannot access VLAN1, VLAN2 and VLAN4.
4. VLAN4 members cannot access VLAN1 and VLAN3 members, but they can access VLAN2
members.
Example 3a: The same VLAN members can be at different switches with the same VID
(See Figure 3.7).
Figure 3-6 - Port-based VLAN Diagram
Figure 3.5 - Port-based VLAN Diagram

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4.0 Network Applications
There are three ways to access switch management functions:
1. RS-232 serial port connection (CLI)
2. Telnet
3. Web
Note: Before accessing management functions through Telnet or the Web, you must modify the
IP address, subnet mask, default gateway and DNS through the RS-232 connection.
4.1 Using the RS-232 Serial Port Connection
To configure the switch via the RS-232 serial port connection, follow these steps:
1. Connect the serial cable included with your switch to your workstation.
2. Connect the serial cable to console connector on the back of your switch.
3. Run the terminal emulator (Example: HyperTerminal) using the following settings.
a. Baud rate (bits per second): 57600
b. Data bits: 8
c.Parity: N
d. Stop bits: 1
e. Flow control: None
4. When you complete the connection, press the Enter key.
5. Turn on the switch.
6. The default login is:
a. Username = admin
b. Password = admin
Figure 3-7 Attribute-based VLAN Diagram

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4.2 Configuring IP, Subnet Mask and Default Gateway
The default settings for your switch are listed in the following table:
Default Value GSM2116/GSM2124
IP Address 192.168.1.1
Subnet 255.255.255.0
Default Gateway 192.168.1.254
Table 4-1
You may either change the IP address of the switch or change the IP address of your
workstation. To change the IP address of the switch, via the console connection, you will have
to use the CLI command listed below. A complete list of CLI commands is in Section 6.0 of this
manual.
1. Once you have logged into the switch, you will see the following screen.
Figure 4.1 – Login screen
2. To set the IP Address of the switch, use the following commands:
Syntax:
set ip <ip> <mask> <gateway>
Description:
To set the system IP address, subnet mask and gateway.
Argument:
<ip> : ip address
<mask> : subnet mask
<gateway> : default gateway
Possible value:
<ip> : 192.168.1.2 or others
<mask> : 255.255.255.0 or others
<gateway> : 192.168.1.253 or others
Example:
GEL2-SW8(ip)# set ip 192.168.1.2 255.255.255.0 192.168.1.253

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Once you have set the IP address of the switch, you must save the configuration. The CLI
command is: save start.
A detailed list of CLI commands can be found in Section 6.0.
4.3 Configuring the Switch via the Web
You can configure and monitor the switch through:
CLI
Web browser
SNMP manager. The user interface for SNMP is not covered at this time.
Before you are able to communicate with the switch, you must know the IP address of the
switch. Once you know the IP address, follow these instructions:
1. Connect the switch with a UTP cable to your workstations.
Note: If the workstation connects to the switch, you will have to setup the same subnet
mask between them.
2. Access your web browser or use the console connection.
Note: If you make changes to the configuration, you must save the configuration before
rebooting the switch.
Assign an IP address,
For example:
IP = 192.168.1.100
Subnet Mask = 255.255.255.0
D
e
f
au
l
t
Gate
w
ay
= 1
9
2.1
68
.1.2
5
4 Fi
g
ure 4.2
Ethernet LAN

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Figure 4.3 - Login Screen via a Web browser
4.4 IP Address Assignment
For IP address configuration, the following three parameters are required:
IP address
Subnet Mask
Default Gateway and DNS.
IP Address:
The address of the network device is used for internetworking communication. IP addresses are
split into predefined address classes or categories. This is referred to as “classful” addressing
because the address is spilt into three predefined classes, groupings or categories. Each IP
address comprises two parts: network identifier (address) and host identifier (address). The
network identifier identifies the network on which the host resides, while the host identifier
identifies the particular host on the given network. The host identifier must be unique in the
same LAN. Each class has its own network range between the network identifier and host
identifier in the 32 bits address. IP address is known as IPv4.
Network identifier Host identifier
With “classful” addressing, the IP address is divided into three classes: class A, class B and
class C. The rest of IP addresses are for multicast and broadcast. The bit length of the network
prefix is the same as that of the subnet mask and is denoted as IP address/X, for example,
192.168.1.0/24. Each class has its address range described below.
32 bits

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Class A:
Address is less than 126.255.255.255. There are a total of 126 networks can be defined
because the address 0.0.0.0 is reserved for default route and 127.0.0.0/8 is reserved for
loopback function.
0
Class B:
IP address range between 128.0.0.0 and 191.255.255.255. Each class B network has a 16-bit
network prefix followed 16-bit host address. There are 16,384 (2^14)/16 networks able to be
defined with a maximum of 65534 (2^16 –2) hosts per network.
10
Class C:
IP address range between 192.0.0.0 and 223.255.255.255. Each class C network has a 24-bit
network prefix followed 8-bit host address. There are 2,097,152 (2^21)/24 networks able to be
defined with a maximum of 254 (2^8 –2) hosts per network.
110
Class D and E:
Class D is a class with first 4 MSB (most significance bit) set to 1-1-1-0 and is used for IP
Multicast. See also RFC 1112. Class E is a class with first 4 MSB set to 1-1-1-1 and is used for
IP broadcast.
According to IANA (internet assigned numbers authority), there are three specific IP address
blocks reserved and able to be used for extending internal networks. This is referred to as
Private IP address and listed below:
Class A 10.0.0.0 --- 10.255.255.255
Class B 172.16.0.0 --- 172.31.255.255
Class C 192.168.0.0 --- 192.168.255.255
Please refer to RFC 1597 and RFC 1466 for more information.
Subnet mask:
Bit # 0 1 7 8 31
Network address Host address
Bit # 01 2 15 16 31
Network address Host address
Bit # 0 1 2 3 23 24 31
Network address Host

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Subnet mask is the sub-division of a class-based network or a CIDR block. The subnet is used
to determine how to split an IP address to the network prefix and the host address in bitwise
basis. It is designed to utilize the IP address more efficiently and make it easier to manage IP
networks.
For a class B network, 128.1.2.3, the subnet mask 255.255.0.0 in default, in which the first two
bytes are all 1s. This means more than 60 thousands of nodes in flat IP address will be at the
same network. This is too large to manage practically. Now if we divide it into a smaller network
by extending network prefix from 16 bits to, say 24 bits, its third byte is used to subnet this class
B network. Now it has a subnet mask 255.255.255.0, in which each bit of the first three bytes is
1. It’s now clear that the first two bytes is used to identify the class B network, the third byte is
used to identify the subnet within this class B network and, of course, the last byte is the host
number.
Not all IP addresses are available in the sub-netted network. Two special addresses are
reserved. They are the addresses with all zero’s and all one’s. For example, an IP address
128.1.2.128, what will the reserved IP address look like? All 0s mean the network itself, and all
1s mean IP broadcast.
In this diagram, the subnet mask with 25-bit long, 255.255.255.128, contains 126 members in
the sub-netted network. The length of network prefix equals the number of the bit with 1s in that
subnet mask. With this, you can easily count the number of IP addresses matched. The
following table shows the result.
10000000.00000001.00000010.1 0000000
128.1.2.128/25
25 bits
1 0000000
1 1111111
All 0s = 128.1.2.128
All 1s= 128.1.2.255
SubneNetwork

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Prefix Length No. of IP matched No. of Addressable IP
/32 1 -
/31 2 -
/30 4 2
/29 8 6
/28 16 14
/27 32 30
/26 64 62
/25 128 126
/24 256 254
/23 512 510
/22 1024 1022
/21 2048 2046
/20 4096 4094
/19 8192 8190
/18 16384 16382
/17 32768 32766
/16 65536 65534
Table 4-2
According to the scheme above, a subnet mask 255.255.255.0 will partition a network with the
class C. This means there will be a maximum of 254 effective nodes existing in this sub-netted
network and is considered a physical network in an autonomous network. It owns a network IP
address which may look like 168.1.2.0.
With the subnet mask, a bigger network can be divided into smaller pieces. If you want to have
more than two independent networks in a LAN, the network must be partitioned. The subnet
mask must be applied.
For different network applications, the subnet mask may look like 255.255.255.240. This means
it is a small network accommodating a maximum of 15 nodes in the network.
Default Gateway:
For the routed packets, if the destination is not in the routing table, all traffic is put into the
device with the designated IP address, known as default router. Basically, it is a routing policy.
The gateway setting is used for Trap Events Host only in the switch.
For assigning an IP address to the switch, check the IP address of the network that will be

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connected to the switch. Use the same network address and append your host address.
Figure 4.4 – IP Configuration
First, IP Address: as shown in the Figure 4.4, enter “192.168.1.1”, for instance. An IP address
such as 192.168.1.x must be set on your PC.
Second, Subnet Mask: as shown in the Figure 4.4, enter “255.255.255.0”. Any subnet mask
such as 255.255.255.x is allowable in this case.
DNS:
The Domain Name Server translates the human readable machine name to IP address. Every
machine on the Internet has a unique IP address. A server generally has a static IP address. To
connect to a server, the client needs to know the IP of the server. However, generally the name
is used to connect to the server. Thus, the switch DNS client program (such as a browser) will
ask the DNS to resolve the IP address of the named server.