Cabletron Systems 04-0053-01 Manual De Usuario

SmartSwitch ATM User Guide   8-3

ATM Filtering and Clocking

Port Clock Configuration  

By setting the mask appropriately, a filter could either admit or deny access to all but a few addresses within a range. 
For example, if a filter’s mask is set to 

, the 

filter disregards the first byte when comparing addresses. As another example, if the filter’s mask is set to 

, the filter disregards the last two bits of the 

first byte of the address (

) when comparing addresses.

If a filter’s mask is shorter than its corresponding ATM address, the mask starts at the most significant bit, and pads 
the remaining length (equal to the length of the specified ATM address) with zero bytes (00). For example, if a filter 
address is specified as 

, and the mask for that 

address is specified as 

, the SmartSwitch ATM switch treats the mask as 

.

8.1.4

Filter Considerations Regarding LANE and IP over ATM

It’s important to remember that ATM address filters and filter sets cannot restrict communication between clients who 
are members of the same ELAN. For example, client 1 and client 2 are members of the same ELAN. For some reason 
it’s necessary to restrict client 1 from communicating with client 2. A filter is created and assigned to the port through 
which client 1 connects the SmartSwitch ATM switch. The filter denies client 1 access to client 2 by rejecting the call 
set up to client 2. However, once the call fails, client 1 resorts to broadcasting to client 2 through the ELAN’s BUS. In 
turn, the BUS forwards the broadcast packets to client 2 and contact between client 1 and client2 is established.

ATM address filtering under LANE is more effective if the filter denies a client the ability to join an ELAN. In the 
example above, client 1 could be kept from communicating with client 2 if client 1 first needed to join client 2’s ELAN. 
In this case, a filter is created that denies client 1 the destination of the LANE servers. As a result client 1 cannot join 
client 2’s ELAN and the two are kept from communicating.

ATM address filtering are more effective in an IP over ATM VLAN environment. Clients connect to each other by 
obtaining address information form the ARP server. Once the address information is obtained, clients connect directly 
to each other through the switch’s ports. Because of the client-to-client connection method of IP over ATM, filter sets 
assigned to strategic ports, can effectively control (admit or deny) entities attempting to set up calls through the VLAN.

8.2

PORT CLOCK CONFIGURATION

The port clock features described below are supported by the SmartSwitch 6500 
only.

The SmartSwitch 6500 allows the specifying source of clocking on a per-port basis. The following describes the 
possible clock modes:

Local — The port derives its clocking signal from its own oscillator

Loopback — The port derives its clocking signal from the clock signal transmitted to it from the 
device (switch, etc.) to which it’s attached

Network — The port derives its clocking signal from a clock signal received on some port of the 
switch and made available through the backplane to all ports