HP 2500 manual Port IP, Analysis of IP Mask for Multiple-Station Entries

Port IP

Using Passwords, Port Security, and Authorized IP Managers To Protect Against Unauthorized Access

Using IP Authorized Managers

		Table 7-3.		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	The “255” in the first three octets of the mask specify that only the exact
Authorized	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
Manager IP
					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	In this example (figure 7-16, below), the IP mask allows a group of up to
Authorized	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
IP Address
					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.
4th Octet of IP Mask:			249
4th Octet of Authorized IP Address: 5

Using Passwords, Security, and Authorized

Bit Numbers	Bit		Bit		Bit		Bit		Bit
	7	6		5		4		3
Bit Values	128	64		32		16		8
4th Octet of
IP Mask (249)
4th Octet of
IPAuthorized
Address (125)

Bit		Bit
2	1
4	2

Bit 0

1

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 of the mask.

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.

Figure 7-16. Example of How the Bitmap in the IP Mask Defines Authorized Manager Addresses

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