Waters Network Systems ProSwitch 2800M User manual

12
OPERATING MANUAL
ProSwitch 2800M/MR
Managed Modular Fiber and Copper Switch Chassis
CORPORATE HEADQUATERS MANUFACTURING/CUSTOMER SERVICE
7401 Metro Blvd., Suite 560 945 37th Avenue, NW
Edina, MN 55439 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...................................................................................................................7
3.0 INTRODUCTION..............................................................................................................................7
3.1 HARDWARE FEATURES...........................................................................................................7
3.2 SOFTWARE FEATURES...........................................................................................................7
3.3 UPLINK MODULES..................................................................................................................8
3.4 REDUNDANT POWER .............................................................................................................8
3.5 HARDWARE DESCRIPTION......................................................................................................9
3.6 LEDS...................................................................................................................................9
3.6 LEDS.................................................................................................................................10
3.7 REAR PANEL ....................................................................................................................... 11
3.8 INSTALLATION......................................................................................................................11
3.9 OPTIONAL SFP MODULES....................................................................................................11
3.10 POWER ON.........................................................................................................................11
3.11 SWITCH TOPOLOGY............................................................................................................. 11
3.11.1 CABLING REQUIREMENTS FOR SFPMODULE....................................................................12
3.11.2 CABLE BIT-TIME..............................................................................................................12
4.0 ACCESS TO MANAGEMENT FUNCTIONS.................................................................................15
4.1 USING THE RS-232 SERIAL PORT CONNECTION ...................................................................15
4.2 CONFIGURING IP, SUBNET MASK AND DEFAULT GATEWAY.....................................................16
4.3 CONFIGURING THE SWITCH VIA THE WEB..............................................................................16
4.4 IPADDRESS ASSIGNMENT....................................................................................................17
5.0 WEB BASED MANAGEMENT......................................................................................................22
5.1 OVERVIEW OF WEB MANAGEMENT.......................................................................................23
5.2 SYSTEM INFORMATION.........................................................................................................27
5.3 IPCONFIGURATION..............................................................................................................28
5.4 TIME CONFIGURATION..........................................................................................................30
5.5 ACCOUNT CONFIGURATION ..................................................................................................32
5.6 MANAGEMENT POLICY.........................................................................................................33
5.7 VIRTUAL STACK ...................................................................................................................35
5.8 PORT CONFIGURATION ........................................................................................................37
5.8.1 PORT STATUS......................................................................................................................38
5.8.2 PORT CONFIGURATION ........................................................................................................42
5.8.3 SIMPLE COUNTER................................................................................................................43
5.8.4 DETAIL COUNTER ................................................................................................................44
5.9 SNMP CONFIGURATION.......................................................................................................48
5.10 DHCP BOOT.......................................................................................................................49
5.11 IGMP SNOOPING ................................................................................................................50
5.12 VLANS..............................................................................................................................53
5.12.1 VLAN MODE..................................................................................................................53
5.12.2 TAG-BASED GROUP........................................................................................................54
5.12.3 PVID..............................................................................................................................57
5.12.4 PORT-BASED GROUP.......................................................................................................58
5.13 MAC TABLE ........................................................................................................................60
5.14 GVRPCONFIGURATION.......................................................................................................65
5.15 SPANNING TREE CONFIGURATION (STP) CONFIGURATION.....................................................69
5.15.1 STPSTATUS..................................................................................................................69
5.15.2 CONFIGURATION.............................................................................................................71
5.15.3 STPPORT CONFIGURATION............................................................................................73

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5.16 TRUNKING CONFIGURATION .................................................................................................75
5.17 802.1X CONFIGURATION......................................................................................................79
5.18 ALARM CONFIGURATION ......................................................................................................88
5.19 CONFIGURATION..................................................................................................................90
5.19.1 SAVE/RESTORE...............................................................................................................92
5.19.2 CONFIGURATION FILE......................................................................................................94
5.20 SECURITY ...........................................................................................................................95
5.21 BANDWIDTH MANAGEMENT..................................................................................................98
5.22 QOS(QUALITY OF SERVICE)CONFIGURATION.....................................................................101
5.23 DIAGNOSTICS.................................................................................................................... 112
5.24 TFTPSERVER ..................................................................................................................114
5.25 LOG.................................................................................................................................. 115
5.26 FIRMWARE UPGRADE.........................................................................................................116
5.27 REBOOT............................................................................................................................ 117
5.28 LOGOUT............................................................................................................................118
6.0 OPERATION OF CLI MANAGEMENT .....................................................................................119
6.1 LOGIN...............................................................................................................................119
6.2 COMMANDS OF CLI ...........................................................................................................120
7.0 MAINTENANCE...........................................................................................................................142
7.1 EXAMPLES ........................................................................................................................142
8.0 TROUBLESHOOTING.................................................................................................................143
8.1 BEFORE CALLING FOR ASSISTANCE....................................................................................143
8.2 RETURN MATERIAL AUTHORIZATION (RMA) PROCEDURE ....................................................144
8.3 SHIPPING AND PACKAGING INFORMATION............................................................................144
9.0 WARRANTY ................................................................................................................................145

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1.0 Specifications
OPERATIONAL CHARACTERISTICS
MAC Address Table: 8K
Switching Mode: Store-and-forward
Memory Buffer Size:
256Kb packet buffer
128Kb control buffer
PERFORMANCE
Non-blocking wire speed
Auto negotiation
Auto-MDIX
Back pressure flow control for half duplex
Flow control for full duplex
Filtering/Forwarding Rate Performance
10Mbps: 14,880 pps
100Mbps: 148,800 pps
1000Mbps: 1,488,000 pps
LED INDICATORS
Per port: Power; Link/Activity; FDX; speed
System LED Power
NETWORK STANDARDS
IEEE 802.3
IEEE 802.3u
IEEE 802.3z
IEEE 802.3ad
IEEE 802.3ab
IEEE 802.3x
IEEE 802.1p/q
IEEE 802.1d/w
IEEE 802.1x
MANAGEMENT FUNCTIONS
Web-based, SNMP, CLI, or Telnet
RMON
RFC1757 group 1, 2, 3 and 9
DHCP client
IGMP snooping function
802.1x port-based authentication
QoS (four levels)
VLANs 4094/Maximum 256 groups

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GVRP
Port mirroring
Port trunking
Flow control
Port security
Static MAC address security
TFTP software upgrade capability
EMI/SAFETY COMPLIANCE
FCC Class A & CE Mark Approval
CABLE CONNECTORS
Copper:
RJ45 shielded female ports
10/100Mbps: CAT5 UTP or better
Console Port:
RS232 Cable/DB9 connector
Fiber:
MM FX port: 50/125um, 62.5/125mm
SM FX port: 9/125um
MM SX port: 50/125um, 62.5/125mm
SM LX port: 9/125um
SC, ST and SC connectors
FIBER DISTANCE
100Base-FX
MM: 2km
SM: 20km
1000Base-SX SFPs
MM: 850m
1000Base-LX SFPs
SM: 10km, 1310nm
SM: 40km, 1310nm
POWER SUPPLY
Internal power supply
Input Voltage
100 to 240 VAC, 50 to 60Hz
Power Consumption
45 watts maximum

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OPERATING ENVIRONMENT
Ambient Temperature:
32° to 104°F (0° to 40°C)
Storage:
-68° to 158°F (20° to 70°C)
Ambient Humidity:
32% to 104% (non-condensing)
MECHANICAL
Enclosure: Rugged high-strength sheet metal suitable for stand alone or rack mountable
Cooling Method: Fan cooled
PHYSICAL CHARACTERISTICS
Dimensions: 17.4 W x 11 D x 1.75” H (442 x 281 x 44mm)
Weight:
2800M Chassis: 7.5 lbs (3.4 kg)
2800MR Chassis: 10 lbs (4.6 kg)
Copper Module: .61 lbs (.28 kg)
Fiber Module: .75 lbs (3.34 kg)
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.
ProSwitch 2800M or MR switch chassis
Modules (sold separately)
Mounting Accessory for (19” rack shelf)
User’s manual
AC power cord
RS-232 Cable
3.0 Introduction
The ProSwitch 2800M is a managed modular switch chassis providing outstanding performance
in any network environment requiring a combination of fiber and copper ports. The 2800M has
three module bays for 10/100Base-TX or 100Base-FX (multi or singlemode) 8 port modules. In
addition to the three module bays, the 2800M has two 10/100/1000Base-TX ports and two mini
GBIC slots for 1000Base-SX or 1000Base-LX SFP modules, providing a total of 28 usuable
ports.
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.
3.1 Hardware Features
The 2800M 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
256KB packet buffer
Maximum useable ports is 28
Programmable classifier for QoS
8K MAC address and 4K VLAN support (IEEE802.1Q)
Per-port shaping, policing, and broadcast storm control
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
3.2 Software Features
The following lists management highlights of the 2800M switch:
Supports concisely the status of ports and easily port configuration
Supports per port traffic monitoring counters

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Supports a snapshot of the system Information upon login
Port mirror function
Static trunk function
Supports 802.1Q VLAN with 256 entries
User management limited to three users; only first admin can configure device
DHCP broadcasting suppression to avoid network suspensions or crashes
Sends traps events while monitoring
Default configuration can be restored to overwrite the current configuration which can be
used via web browser and CLI
Supports on-line plug/unplug SFP modules
Supports five types of QoS: MAC Priority, 802.1p Priority, IP TOS Priority, and DiffServ
DSCP Priority
Built-in web-based and CLI management and CLI management
Rapid spanning tree (802.1w RSTP)
802.1x port security on a VLAN
SNMP access can be disabled to prevent illegal SNMP access
Support Ingress, Non-Unicast, and Egress bandwidth rating management
The trap events and alarm messages can be transferred via e-mail and mobile phone short
messages service
Supports diagnostics informing administrator of hardware status
Supports external loopback test to check if link is OK
TFTP for firmware upgrade, system log upload, and config file import/export
Remote boot the device through user interface and SNMP
Network time synchronization and daylight saving
Records 120 event logs in main memory and displays on the local console
3.3 Uplink Modules
The following module configurations are available for the 2800M/MR.
2800-8TX
8-port 10/100Base-TX module with RJ45 connectors
2800-8FXSC
8-port 100Base-FX MM fiber module with SC connectors
2800-8FXST
8-port 100Base-FX MM fiber module with ST connectors
2800-8SMSC-20
8-port 100Base-FX SM (20km, 1310nm) fiber module with SC connectors
SFP-1000SXLC
1-port 1000Base-SX MM fiber module with LC connector
SFP-1000LXLC
1-port 1000Base-LX SM (10km) fiber module with LC connector
SFP-1000SXLC
1-port 1000Base-LX SM (30km) fiber module with LC connector
3.4 Redundant Power
Optional redundant power is available for the 2800MR model.
2800-PWR-AC/DC
1U AC/DC power module
2800-PWR-DC/DC
1U DC/DC power module

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3.5 Hardware Description
Figure 3.1 - 2800M Switches with Copper and Fiber Modules
Power Indication LED
Fast Ethernet Port
LED SET Mode:
ACT/FDX/SPD
Gigabit
Dual
Media
Port:
SFP/TP
Fiber Port Status: Link
LEDSET Button
LEDSET button is
used to change
the LED display
mode
Fiber Port Status: ACT/FDX/SPD
RESET Button:
RESET button is used to
reset the management
system.
Figure 3.2 - Front View of 2800M Switch with Fiber Modules

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3.6 LEDs
The following table provides the status and description of the LEDs:
LED
Color
Function
System LED
CPURUN
Green
Blinks when CPU is on and good
POWER
Green
Switch is receiving power
ACT
Green
Lit when LEDSET set on active mode
FDX
Green
Lit when LEDSET set on full-duplex mode
SPD
Green
Lit when LEDSET set on speed mode
10/100Mbps Ethernet Port 1 to 8 of 3 Module LED
LNK Green
Port has established a valid link
Off when there is no connection
ACT/FDX/SPD
Amber
(TP Port 1 to
8
of 3 module LED)
Green
(Fiber Port 1 to 8
of 3 module 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 are occurring
c. LEDSET set on SPD (speed) mode:
Lit when 100Mbps speed is active
Off when 10Mbps speed is active
10/100/1000Mbps Gigabit TP/Fiber Port 25, 26 LED
LNK Green Lit when connection with remote device is good
Off when there is no connection
FB Green
Lit when fiber port is active
Off when copper 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 are occurring
c. LEDSET set on SPD (speed) mode:
Lit when 1000Mbps speed is active
Off when 10/100Mbps speed is active
Table 3.1 – LED Staus

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3.7 Rear Panel
Located on the rear panel is the RS-232 DB-9 interface which is used for switch management
configuration.
3.8 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.
3.9 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.
3.10 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.
3.11 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.
Figure 3.4 - Rear View of 2800M
RS-232 DB-9 Connector
AC Line 100-240V 50/60 Hz

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3.11.1 Cabling Requirements for SFP Module
The GSM2800M has four slots for SFP modules. These slots provide fiber connectivity for
Gigabit Ethernet and are optional. The switch supports both multimode and singlemode fiber
connectivity. The following table lists the types of fiber that are supported by the GSM2800M/MR.
IEEE 802.3z
Gigabit Ethernet
1000SX 850nm
Multimode Fiber Cable and Modal Bandwidth
Multimode 62.5/125µm Multimode 50/125µm
Modal
Bandwidth Distance Modal Bandwidth Distance
160MHz-Km 220m 400MHz-Km 500m
200MHz-Km 275m 500MHz-Km 550m
1000Base-
LX/LHX/XD/ZX
Singlemode Fiber 9/125µm
Singlemode transceiver 1310nm 10Km
Singlemode transceiver 1550nm 30, 50Km
1000Base-LX
Singlemode
(BIDI LC)
Singlemode
*20km TX (Transmit) 1310nm
RX (Receive) 1550nm
Singlemode
*20km TX (Transmit) 1550nm
RX (Receive) 1310nm
Table 3.2 – Fiber Cable
3.11.2 Cable Bit-Time
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 3.3 – Cable Bit-Time
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

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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).
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.
Figure 3.4 - No VLAN Configuration Diagram
Figure 3.5 - Port-based VLAN Diagram

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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

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4.0 Access to Management Functions
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): 115200
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
GSM2800M/MR
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
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.
Figure 4.2 – Ethernet Port Connection
Assign an IP address,
For example:
IP = 192.168.1.100
Subnet Mask = 255.255.255.0
Default Gateway = 192.168.1.254
Ethernet LAN

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Before you are able to communicate with the switch, you must know the IP address of the
switch. The default IP setting for the 2800M is:
IP = 192.168.1.100
Subnet Mask = 255.255.255.0
Default Gateway = 192.168.1.253
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.
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

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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.
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
32 bits
Bit # 0 1 7 8 31
Network address Host address
Bit # 01 2 15 16 31
Network address Host address

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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
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.
Bit # 0 1 2 3 23 24 31
Network address Host

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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.
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
/2
4
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
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
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