HP 6120 Figure 12-6.Analysis of IP Mask for Multiple-StationEntries

Using Authorized IP Managers

Building IP Masks

Figure 12-6. Analysis of IP Mask for Multiple-Station Entries

1st	2nd	3rd	4th	Manager-Level or Operator-Level Device Access
Octet	Octet	Octet	Octet

IP Mask	255	255	255	0
Authorized	10	28	227	125
Manager IP

The “255” in the first three octets of the mask specify that only the exact 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.

IP Mask	255	255	255	249
Authorized	10	28	227	125
IP Address

In this example (figure 12-7, below), the IP mask allows a group of up to 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 12-7. 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
IPAuthorized
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.

12-12