Adder Technology AdderLink IP manual Calculating the mask for IP access control, Single locations

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Calculating the mask for IP access control

The IP access control function uses a standard IP address and a net mask notation to specify both single locations and ranges of addresses. In order to use this function correctly, you need to calculate the mask so that it accurately encompasses the required address(es).

Single locations

Some of the simplest addresses to allow or deny are single locations. In this case you enter the required IP address into the ‘Network/Address’ field and simply enter the ‘Mask’ as 255.255.255.255 (255 used throughout the mask means that every bit of the address will be compared and so there can only be one unique address to match the one stated in the ‘Network/Address’ field).

All locations

The other easy setting to make is ALL addresses, using the mask 0.0.0.0 As standard, the IP access control section includes the entry: +0.0.0.0/0.0.0.0 The purpose of this entry is to include all IP addresses. It is possible to similarly exclude all addresses, however, take great care not to do this as you instantly render all network access void. There is a recovery procedure should this occur.

Address ranges

Although you can define ranges of addresses, due to the way that the mask operates, there are certain restrictions on the particular ranges that can be set. For any given address you can encompass neighbouring addresses in blocks of either 2, 4, 8, 16, 32, 64, 128, etc. and these must fall on particular boundaries. For instance, if you wanted to define the local address range:

192.168.142.67 to 192.168.142.93

The closest single block to cover the range would be the 32 addresses from:

192.168.142.64 to 192.168.142.95.

The mask needed to accomplish this would be: 255.255.255.224

When you look at the mask in binary, the picture becomes a little clearer. The above mask has the form: 11111111.11111111.11111111.11100000

Ignoring the initial three octets, the final six zeroes of the mask would ensure that the 32 addresses from .64 (01000000) to .95 (01011111) would all be treated in the same manner. See Net masks - the binary explanation for details.

When defining a mask, the important rule to remember is:

There must be no ‘ones’ to the right of a ‘zero’.

For instance, (ignoring the first three octets) you could not use a mask that had 11100110 because this would affect intermittent addresses within a range in an impractical manner. The same rule applies across the octets. For example, if you have zeroes in the third octet, then all of the fourth octet must be zeroes.

The permissible mask values (for all octets) are as follows:

Mask octet

Binary

Number of addresses encompassed

255

11111111

1 address

254

11111110

2 addresses

252

11111100

4 addresses

248

11111000

8 addresses

240

11110000

16 addresses

224

11100000

32 addresses

192

11000000

64 addresses

128

10000000

128 addresses

0

00000000

256 addresses

If the access control range that you need to define is not possible using one address and one mask, then you could break it down into two or more entries. Each of these entries could then use smaller ranges (of differing sizes) that, when combined with the other entries, cover the range that you require.

For instance, to accurately encompass the range in the earlier example:

192.168.142.67 to 192.168.142.93

You would need to define the following six address and mask combinations in the IP access control section:

Network/address entry

Mask entry

 

192.168.142.67

255.255.255.255

defines 1 address (.67)

192.168.142.68

255.255.255.252

defines 4 addresses (.68 to .71)

192.168.142.72

255.255.255.248

defines 8 addresses (.72 to .79)

192.168.142.80

255.255.255.248

defines 8 addresses (.80 to .87)

192.168.142.88

255.255.255.252

defines 4 addresses (.88 to .92)

192.168.142.93

255.255.255.255

defines 1 address (.93)

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Contents AdderLink IP Contents Index Four simultaneous remote users Local userModem/ISDN port IP network/InternetAdderView IP features front and rear What’s in the box What you may additionally need    Mounting Single unit rack bracketsDouble unit rack brackets  Host computer or KVM switch ConnectionsLocal keyboard, video monitor and mouse IP network portTo connect a local keyboard, video monitor and mouse To connect the IP network portPower supply connection To connect the power supplyModem/ISDN port To connect a modem or Isdn portPower control port To connect and address the switch boxesInitial configuration Part 1 Local configurationPart 1 Local configuration Part 2 Remote configurationTo perform the initial local configuration Admin passwordTime and Date EncryptionEncryption settings AdderLink IP encryption settingsViewer encryption settings EncryptionWhich restore setting do I use? To restore mouse operation when hot pluggingHot plugging and mouse restoration Recognising an IntelliMouse-style mouseResetting the configuration AdderLink IP asks for an unknown admin passwordTo invoke a configuration reset by switch AdderLink IP does not display the configuration sequencePart 2 Remote configuration To perform the remote configurationNetworking issues Port settingsPositioning AdderLink IP in the network Placing AdderLink IP behind a firewallAddressing To discover a DHCP-allocated IP addressDNS addressing Firewall/router addressPorts Placing AdderLink IP alongside the firewallEnsuring sufficient security Power switching configuration Power control sequencesTo configure the power sequences for each host computer To control two or more ports simultaneouslyPerforming a flash upgrade To perform a flash upgradeConfigure network option Important Wait until the upgrade is completeConnecting to the AdderLink IP Local connectionTo make a local connection To view the local control menuRemote connections To avoid the ‘hall of mirrors’ effectTo connect using the VNC viewer To connect using your Web browserRemote connection by VNC viewer Remote connection by Web browserMenu bar Using the viewer windowWhen using the viewer window Configure Mouse pointersHost selection To select a hostAccess mode shared/private Power controlAuto calibrate Re-synchronise mouseControls Setting the Threshold manually PhaseContrast  If you need to enter a port number Connecting via dial up modem or Isdn linkDownloading VNC viewer from the AdderLink IP Viewer encryption settings Supported web browsersWindows LinuxTroubleshooting When logging on using VNC viewer, I cannot enter a usernameGetting assistance US +1 888 275Appendix 1 Local configuration menus To access the local configuration menusUnit configuration Network configuration Modem configuration Reset configuration To reset the AdderLink IP configurationTo clear IP access control Clear IP access controlWhat is IP access control? Appendix 2 VNC viewer connection options Colour/EncodingAuto select Preferred encodingInputs MiscDefaults Reload defaultsSave as defaults Save configuration file asAppendix 3 VNC viewer window options Security Appendix 4 Browser viewer optionsEncoding and colour level Main configuration menu Logged on users Appendix 5 Remote configuration menusTo access the remote configuration menus User accounts Screensaver timeout Hardware VersionFirmware Version Host Keyboard LayoutAdvanced unit configuration Idle timeoutProtocol timeout Force VNC protocolIP gateway IP access controlIP network mask Setting IP access control To define a new IP access control entryTo reorder access control entries To edit/remove access control entriesModem port Serial port configurationPower control port Host configuration To create a new host entryLogging and status To copy and paste the logOccurred Click to clear All log entries Refresh ListNet masks Appendix 6 Addresses, masks and portsIP addresses Net masks the binary explanation Inside a bit-wise and functionBinary equivalent Binary octet afterCalculating the mask for IP access control Single locationsAll locations Address rangesRouter/firewall address Security issues with portsPorts RS232 serial mouse to PS/2 converter cable Appendix 7 Cable and connector specificationsAdderLink IP to power switch cable Appendix 8 Hotkey sequence codes Other products in the Adder range WarrantySafety information FCC Compliance Statement United States Radio Frequency EnergyEuropean EMC directive 89/336/EEC United States of America Index 

AdderLink IP specifications

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