Cabletron Systems 1800 How Filte r Masks Work

15-4 Smart Switch 1800 4. 0 User Guide , Rev 0 1
Figure 15-2 IPX SAP Filter Record
[A], [A ], [E ], [F] ,[ B] fro m Main Menu
How Filte r Masks Work
Each IPX filter parameter ex cept Filter Name and Server Name is assigned a value and
an associated mask. The mask determines (by the process described below) whether
the filter will be applied to the packet.
The binary bits of the mask will be "ANDed" (0+0=0, 0+1=0, 1+1=1) to the value, as
in this example:
Assume the value (hex) is 1234 and the mask is F000. The binary "ANDing" is as
follows:
Value: 0001001000110100
Mask: 1111000000000000
AND Result: 0001000000000000
The mask will also be ANDed to its corresponding field in each IPX packet as deter-
mined by IPX Filter Applications. This result will be compared to the AND resu lt of
the configured value and mask. If the two results match, the filter w ill be applied. This
process allows a number of packet field values to match the AND result of the mask
and value; for example:
Packet field = 1233, Mask = F 000: Packet field = 1237, Mask = F000:
Binary val ue : 0001001000110011 Value: 0001001000110111
Mask: 1111000000000000 Mask: 1111000000000000
AND Result: 0001000000000000 AND Result: 0001000000000000
IPX Filter Definitions
* Filter Category 1–SAP
* Fil t e r ID 1
A Filter Name filter_zxy
B Ser vice Type Value 0004
C Service Typ e Mask 000f
D Server Name server_123
E Network Address Value ff00ac00
F Network Address Mask ffff0000
G Node Address Value 10ac45000001
H Node Address Mask ffffff000000
I Socket Address Value 4000
J Socket Address Mask f000
Option: