Waters Network Systems PS-2126M-POE User manual

12
OPERATING MANUAL
PS-2126M-POE Switch
Managed Switch with Twenty Four 10/100Base-TX PoE Ports
Plus Two Mini GBIC Slots for 1000Base-SX or LX Fiber Connectivity
Or
10/100/1000Base-TX Copper Connectivity
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 OPTIONAL SFPMODULES ............................................................................................................10
3.5 INSTALLATION...............................................................................................................................10
3.6 OPTIONAL SFPMODULES ............................................................................................................10
3.7 TPPORT AND CABLE INSTALLATION ..............................................................................................10
3.8 POWER ON..................................................................................................................................10
3.9 INSTALLING CHASSIS TO A 19-INCH WIRING CLOSET RAIL...............................................................11
3.10 SWITCH TOPOLOGY...................................................................................................................... 11
4.0 NETWORK APPLICATIONS.........................................................................................................14
4.1 USING THE RS-232 SERIAL PORT CONNECTION ............................................................................14
4.2 CONFIGURING IP, SUBNET MASK AND DEFAULT GATEWAY..............................................................14
5.0 WEB BASED MANAGEMENT......................................................................................................22
5.1 OVERVIEW OF WEB MANAGEMENT................................................................................................23
5.2 SYSTEM INFORMATION..................................................................................................................26
5.3 IPCONFIGURATION ......................................................................................................................27
5.4 TIME CONFIGURATION ..................................................................................................................29
5.5 ACCOUNT CONFIGURATION...........................................................................................................31
5.6 MANAGEMENT POLICY..................................................................................................................32
5.7 VIRTUAL STACK............................................................................................................................34
5.8 PORT CONFIGURATION .................................................................................................................36
5.8.1 PORT STATUS ..............................................................................................................................36
5.8.2 PORT CONFIGURATION .................................................................................................................39
5.8.3 SIMPLE COUNTER ........................................................................................................................40
5.8.4 DETAIL COUNTER.........................................................................................................................41
5.9 POEFUNCTION............................................................................................................................45
5.10 SNMPCONFIGURATION ...............................................................................................................47
5.11 DHCPBOOT ...............................................................................................................................49
5.12 IGMPSNOOPING.........................................................................................................................50
5.13 VLANS........................................................................................................................................52
5.13.1 VLAN MODE ...........................................................................................................................52
5.13.2 TAG-BASED GROUP..................................................................................................................54
5.13.3 PVID......................................................................................................................................56
5.13.4 PORT-BASED GROUP...............................................................................................................57
5.14 MACTABLE................................................................................................................................59
5.15 GVRPCONFIGURATION...............................................................................................................64
5.16 SPANNING TREE CONFIGURATION (STP) CONFIGURATION..............................................................68
5.16.1 STPSTATUS ...........................................................................................................................68
5.16.2 STPCONFIGURATION ..............................................................................................................70
5.16.3 STPPORT CONFIGURATION.....................................................................................................71
5.17 TRUNKING CONFIGURATION .........................................................................................................73
5.18 802.1X CONFIGURATION .............................................................................................................78
5.19 ALARM CONFIGURATION ...............................................................................................................86
5.20 CONFIGURATION ..........................................................................................................................88
5.20.1 CONFIGURATION FILE...............................................................................................................89

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5.20.2 RESTORE DEFAULT CONFIGURATION.........................................................................................90
5.20.3 CONFIGURATION FILE...............................................................................................................92
5.21 SECURITY....................................................................................................................................93
5.22 BANDWIDTH MANAGEMENT...........................................................................................................95
5.23 QUALITY OF SERVICE (QOS) CONFIGURATION ...............................................................................97
5.24 DIAGNOSTICS.............................................................................................................................105
5.25 TFTPSERVER...........................................................................................................................108
5.26 LOG DATA ..................................................................................................................................108
5.27 FIRMWARE UPGRADE .................................................................................................................110
5.28 REBOOT .................................................................................................................................... 111
5.29 LOGOUT .................................................................................................................................... 111
6.0 OPERATION OF CLI MANAGEMENT........................................................................................113
6.1 LOGIN........................................................................................................................................113
6.2 COMMANDS OF CLI....................................................................................................................114
7.0 MAINTENANCE...........................................................................................................................133
7.1 EXAMPLES.................................................................................................................................133
8.0 TROUBLESHOOTING.................................................................................................................134
8.1 BEFORE CALLING FOR ASSISTANCE.............................................................................................134
8.2 RETURN MATERIAL AUTHORIZATION (RMA) PROCEDURE .............................................................135
8.3 SHIPPING AND PACKAGING INFORMATION.....................................................................................136
9.0 WARRANTY ................................................................................................................................137

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1.0 Specifications
OPERATIONAL CHARACTERISTICS
MAC Address Table
8K
Switching Mode
Store-and-forward
Memory Buffer Size
256Kb
128K control memory
Performance
Non-blocking wire speed
Auto negotiation
Auto-MDIX
Back pressure flow control for half duplex
Flow control for full duplex
Maximum throughput is 8.8Gbps
MANAGEMENT FUNCTIONS
Web-based, SNMP (v1, v2c), CLI, or Telnet
Port setting for duplex and speed
MAC based Port trunking
Port based and tagged VLANs (up to 256)
IGMP snooping
802.1x access control
GVRP/GARP
Port mirroring
Broadcast storm suppression
QoS
LACP with auto link fail-over support
STP/RSTP
VSM (supports 16 stacking devices)
Enterprise MIB
RMON
RFC1213MIB (MIB-II)
RFC1757 Bridge MIB
RFC1493 Bridge MIB
RFC1643 Ethernet MIB
NETWORK STANDARDS:
IEEE 802.3
IEEE 802.3u
IEEE 802.3ab
IEEE 802.3af
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
PoE SPECIFICATIONS:
Endpoint with 48VDC power through RJ45 pins 1, 2, 3 and 6
PoE-PSE activity LED indicator
185 watts of total power (up to 15.4 watts for 12 ports and up to 7.7 watts for 24 ports)
Auto detect powered device and consumption levels
Supports per port power consumption monitoring
Smart feature for:
PD on/off
PD detection
Powerlevel
PD status
Power feeding priority
Circuit protection to prevent power interference between ports
Supports per port PoE state setting
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
210 watts maximum
Total power for PoE: 185 watts
OPERATING ENVIRONMENT
Ambient Temperature:
32° to 122°F (0° to 50°C)
Ambient Humidity
5% to 90%
MECHANICAL:
Enclosure:
Rack mountable
Cooling Method: Fan cooled
PHYSICAL CHARACTERISTICS
Dimensions: 14.41 x 17.4 x 1.77 in
366 x 442 x 45 mm
Weight:: 6.83lbs (3.1kg)
WARRANTY:
Limited Lifetime Made in USA

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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.
PS-2126M-POE Ethernet switch chassis
SFP Modules (optional)
Mounting Accessory for (19” rack shelf)
User’s manual
AC power cord
RS-232 Cable
3.0 Introduction
The Waters’ PS-2126M-POE switch is a managed Ethernet switch chassis with twenty four
10/100Base-TX PoE ports and two dual media slots. The dual media slots can be used for
either 10/100/1000Base-TX ports or 1000Base-SX or LX fiber. The switch provides 26 usable
ports.
The PS-2126M-POE meets all IEEE802.3/u/x/z specifications. 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 applications.
For upgrading firmware, please refer to Section 5.27 for more details. The switch will not stop
operating while upgrading firmware, however, upon completion, the switch must be rebooted.
3.1 Hardware Features
The PS-2126M 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
24 auto sensing 10/100 ports
Two 10/100/1000Base-TX or 1000Mbps SFP Fiber module slots
26 usable ports
Supports on-line pluggable fiber transceiver modules
Supports 256KB packet buffer and 128KB control memory
Maximum packet length up to 1536 bytes
Full-duplex flow control (IEEE802.3x) and half duplex backpressure
PoE functions:
•24 port IEEE802.3af PoE PSE
•Endpoint with 48VDC power through RJ45 pins 1, 2, 3 and 6
•Powered device PD auto detection and classification

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•PoE – PSE status and activity LED indicator
3.2 Software Features
The following lists management highlights of the PS-2126M-POE switch:
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
Three user login; only first login administrator can configure the device. The rest of the users
can only view the switch
Maximum packet length can be up to 9208 bytes for jumbo frame application
Supports DHCP broadcasting suppression
Supports five types of QoS: MAC priority, 802.1p priority, IP, TOS Priority and DiffServ DSCP
priority
Supports port mirror function with ingress/egress traffic
Supports rapid spanning tree
Supports 802.1x port security
SNMP access can be disabled to prevent illegal SNMP access
Supports sending of trap events while monitoring events
Supports default configuration which can be restored to overwrite the current configuration
Built-in web-based management and CLI management providing a convenient user interface
Supports network time synchronization and daylight saving
Supports 120 event log records in the main memory and display on the local console
Supports Ingress, non-unicast and Egress bandwidth rating management with a resolution of
1Mbps
Trap event and alarm messages can be transferred via email and mobile phones
Diagnostics available to inform network administrator of hardware status
Supports external loopback test to check to see if the link is okay
TFTP for firmware upgrade
Supports remote boot through user interface and SNMP

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3.3 Hardware Description
Figure 3.1 - Front View of PS-2126M-POE
Figure 3.1 shows the front view of the PS-2126M-POE switch. The switch chassis has twenty
four PoE 10/100Base-TX ports and two dual media slots. Those slots can be used as
10/100/1000Base-TX ports or with SFP modules for 1000Base-SX or LX fiber .
Figure 3.2 shows the rear view of the PS-2126-POE switch.
Figure 3.2 Rear Panel View
Fast Ethernet Port
Power Indication LED
LED SET Mode: ACT/FDX/SPD
Gigabit Dual Media
Port(25~26): SFP/TP
LEDSET Button:
LEDSET button is
used to change
the LED display
mode
PoE Port Status
Indication LEDs Fiber Port Status Indication LEDs
TP Port Status
Indication LEDs
RESET Button:
RESET button is used to
reset the management
s
y
stem.
RS-232 DB-9 Connector
AC Line 100-240V 50/60 Hz

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The following table provides the status and description of the LEDs.
LED Color Function
System LED
CPURUN Green CPU is on and good
POWER Green AC power is on and good
ACT Green LEDSET set on active mode
FDX Green LEDSET set on full-duplex mode
SPD Green LEDSET set on speed mode
10/100Base-TX Ports 1 to 24 LED
LINK Green
Connection with remote device is good
Off when cable connection is not good
ACT/FDX/ SPD Amber
(TP Port 1 to 24 LED)
a. LEDSET set on ACT (active) mode:
Blinks when traffic is present
b. LEDSET set on FDX (full-duplex)
mode:
Lit when full-duplex mode is active
Blinks when collisions occur
c. LEDSET set on SPD (speed) mode:
Lit when 100Mbps speed is active
Off when 10Mbps speed is active
PoE-PSE ACT Green PoE Power is active
10/100/1000Mbps Gigabit TP/Fiber Port 25, 26 LED
LINK Green
Connection with remote device is good
Off when cable connection is not good
FX Green
Fiber port is active
TP port is active
ACT/FDX/
SPD
Green
(Port 25,
26 LED)
a. LEDSET set on ACT (active) mode:
Blinks when traffic is present
b. LEDSET set on FDX (full-duplex)
mode:
Lit when full-duplex mode is active
Blinks when collisions occur
c. LEDSET set on SPD (speed) mode:
Lit when 1000Mbps speed is active
Off when 10/100Mbps speed is
active
Table 3-1 - LEDs

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3.4 Optional SFP Modules
The following lists the SFP modules that are available for this 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
3.5 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.
3.6 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.
3.7 TP Port and Cable Installation
Twisted pair port supports MDI/MDI-X auto-crossover, so both types of cable, straight-
through (Cable pin-outs for RJ-45 jack 1, 2, 3, 6 to 1, 2, 3, 6 in 10/100M TP; 1, 2, 3, 4, 5, 6, 7,
8 to 1, 2, 3, 5, 6, 7, 8 in Gigabit TP) and cross-over (Cable pin-outs for RJ-45 jack 1, 2, 3, 6
to 3, 6, 1, 2) can be used.
Use CAT5 grade RJ45 TP cable to connect to a TP port of the switch to a network-aware
device such as a workstation or a server.
Repeat the above steps for each RJ45 port to be connected to a Gigabit 10/100/1000 TP
device.
3.8 Power On
The switch supports 100-240 VAC, 50-60 Hz power supply. The power supply will automatically
convert the local AC power source to DC power. Power can be turned on even if there are no
connections to the switch ports. Once the power is on, LEDs will light up and then go out
except the power LED.

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Once the self test is performed, the bootloader will load the firmware into the memory, which
takes about 30 seconds. The switch will flash the LEDs once and automatically perform a self
test.
3.9 Installing Chassis to a 19-inch Wiring Closet Rail
Caution: Allow a proper spacing and proper air ventilation for the cooling fan at both sides of
the chassis.
Wear a grounding device for electrostatic discharge.
Screw the mounting accessory to the front side of the switch
Place the chassis into the 19-inch wiring closet rail. Secure the chassis with the screws.
3.10 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.
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 3.3).

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Figure 3.3 - No VLAN Configuration Diagram
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 3-4).
Figure 3.4 - Port-based VLAN Diagram

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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 3-5).
Figure 3.5 - Port-based VLAN Diagram
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 3-6).
Figure 3.6 – Attribute-based VLAN

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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
4.2 Configuring IP, Subnet Mask and Default Gateway
The default settings for your switch are listed in the following table:
Default Value PS-2126M-POE
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.

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1. Once you have logged into the switch, you will see the following screen.
Figure 4.1 – Login Screen
2. To set the IPAddress 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:
FEPoEL2-SW26# set ip 192.168.1.2 255.255.255.0 192.168.1.253
Note: Once you have set the IP address of the switch, you must save the configuration. The
CLI command is: save start. Adetailed list of CLI commands can be found in Section 6.0.

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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
Default Gateway
=
192.168.
1
.
254
Fi
g
ure 4.2
–
Front Switch Vie
w
Ethernet LAN

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4.4 IPAddress Assignment
Figure 4.3 - Login Screen via a Web browser
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.
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.
32 bits

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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:
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
Bit # 0 1 7 8
Network address Host address
Bit # 01 2 15 16
Network address Host address
Bit # 0 1 2 3 23 24 31
Network address Host

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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

Waters Network Systems User’s Manual Page 20
PS-2126M-POE
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