3com 530 Manuel D’Utilisation

 

 

 

Subnet Masking is a mechanism which can be 

 

enabled in computer and communications 

 

equipment which tells the equipment and the 

 

network, which parts of the IP address are to be used 

 

as the 

 

 identifier and which are the 

 

 

 

identifier. 

 

A subnet mask consists of a similar field structure to 

 

that of the IP address (123.123.123.123). For example:

255.255.0.0

 

This means that the first two three digit bytes of the 

 

IP address (the fields 

 

 by - 255.255) are to be 

 

recognized and used as the Network address, and 

 

the last two bytes (those set to .0.0) are to be used to 

 

identify the Host address. 

 

An alternative way of expressing a subnet mask is a 

 

single number indicating how many bits of the IP 

 

address are to be used for the network address. For 

 

example 255.255.0.0 can be expressed as 16 while 

 

255.255.255.192 can be expressed as 24.

 

The OfficeConnect Remote can be configured to use 

 

subnet masking to enable ISDN Autocalls to be made 

 

on groups of IP addresses or on specific IP addresses. 

 

Normally, a subnet mask would be set so that any IP 

 

address, in a range of hosts on a destination LAN which 

 

are detected on the unit’s locally connected LAN port, 

 

causes an ISDN Autocall to be made out to that 

 

destination. 

 

This is achieved by the addition of a 

/xx

 

 number at 

 

the end of the configured address. For example:

193.123.123.123/32 

 

The 

/32

 

 appended to the IP number indicates that all 

 

four of the bytes are used and must have valid entries.

 

A 

/24

 

 mask, for example:

193.123.123.0/24 

 

means that only the first three bytes are to be 

 

recognized and used, and the last byte can be 

 

ignored. In this case, any IP address appearing on the 

 

locally connected LAN in the range 193.123.123.0 to 

 

193.123.123.255 will cause an autocall to be made to 

 

the destination network who’s name is associated 

 

with that number in the ISDN Autocall table. The 

 

name is then looked up in the ISDN Numbers table 

 

and a call made to the ISDN number which has 

 

been assigned to that name. 

Rc.bk : RCAPPA.FRM  Page 13  Thursday, July 10, 1997  9:53 AM