HP 6120G/XG HP ProCurve Series 6120 Blade Switches Access Security Guide - Page 586
Analysis of IP Mask for Multiple-Station Entries
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Using Authorized IP Managers Building IP Masks Figure 14-6. Analysis of IP Mask for Multiple-Station Entries IP Mask Authorized Manager IP IP Mask Authorized IP Address 1st 2nd 3rd 4th Manager-Level or Operator-Level Device Access Octet Octet Octet Octet 255 255 255 0 The "255" in the first three octets of the mask specify that only the exact 10 28 227 125 value in the octet of the corresponding IP address is allowed. However, the zero (0) in the 4th octet of the mask allows any value between 0 and 255 in that octet of the corresponding IP address. This mask allows switch access to any device having an IP address of 10.28.227.xxx, where xxx is any value from 0 to 255. 255 255 255 249 In this example (figure 14-7, below), the IP mask allows a group of up to 10 28 227 125 4 management stations to access the switch. This is useful if the only devices in the IP address group allowed by the mask are management stations. The "249" in the 4th octet means that bits 0 and 3 - 7 of the 4th octet are fixed. Conversely, bits 1 and 2 of the 4th octet are variable. Any value that matches the authorized IP address settings for the fixed bits is allowed for the purposes of IP management station access to the switch. Thus, any management station having an IP address of 10.28.227.121, 123, 125, or 127 can access the switch. Figure 14-7. Example of How the Bitmap in the IP Mask Defines Authorized Manager Addresses 4th Octet of IP Mask: 249 4th Octet of Authorized IP Address: 5 Bit Numbers Bit Bit Bit Bit Bit Bit Bit Bit 7 6 5 4 3 2 1 0 Bit Values 128 64 32 16 8 4 2 1 4th Octet of IP Mask (249) 4th Octet of IP Authorized Address (125) Bits 1 and 2 in the mask are "off", and bits 0 and 3 - 7 are "on", creating a value of 249 in the 4th octet. Where a mask bit is "on", the corresponding bit setting in the address of a potentially authorized station must match the IP Authorized Address setting for that same bit. Where a mask bit is "off" the corresponding bit setting in the address can be either "on" or "off". In this example, in order for a station to be authorized to access the switch: • The first three octets of the station's IP address must match the Authorized IP Address. • Bit 0 and Bits 3 through 6 of the 4th octet in the station's address must be "on" (value = 1). • Bit 7 of the 4th octet in the station's address must be "off" (value = 0). • Bits 1 and 2 can be either "on" or "off". This means that stations with the IP address 13.28.227.X (where X is 121, 123, 125, or 127) are authorized. 14-12