Cabletron Systems 04-0053-01 Port Clock Configuration, FFFFFFFFFFFFFFFFFFFF00000000000000000000

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 00:FF:FF:FF:FF:FF:FF:FF:FF:FF:FF:FF:FF:FF:FF:FF:FF:FF:FF:FF, the

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

FC:FF:FF:FF:FF:FF:FF:FF:FF:FF:FF:FF:FF:FF:FF:FF:FF:FF:FF:FF, the filter disregards the last two bits of the

first byte of the address (FC = 11111100) 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 39:00:00:00:00:00:00:00:00:00:14:41:80:00:20:D4:14:41:80:00, and the mask for that

address is specified as FF:FF:FF:FF:FF:FF:FF:FF:FF:FF, the SmartSwitch ATM switch treats the mask as

FF:FF:FF:FF:FF:FF:FF:FF:FF:FF:00:00:00:00:00:00:00:00:00:00.

8.1.4Filter 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.

8.2PORT CLOCK CONFIGURATION

Note 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

SmartSwitch ATM User Guide 8-3