ATM Addresses and Address Registration

UNI signalling uses ATM addresses for signalling. Every ATM interface has an ATM address in addition to its IP address.

ATM addresses, like Network Service Access Point (NSAP) addresses, are 20 octets long. The End System Identifier (ESI) field within the ATM address is a unique 6 octet value; this can be the IEEE hardware MAC address conventionally associated with every network interface. The Selector field is one octet long. The 13 octets that make up the rest of the ATM address are called the Network Prefix, and are derived from the ATM switch fabric to which the interface is connected. Every ATM switch fabric is configured with a 13 octet prefix.

On a SunATM host, the prefix associated with the local switch fabric is represented by the $prefix variable. Its value is obtained by the system at configuration time.

Figure 5-1 ATM Address Fields

The UNI specification specifies the Interim Local Management Interface (ILMI) service interface for a client to learn and register its ATM address. The ILMI service interface is based on the use of SNMP over AAL5. In the SunATM software package, ILMI service is provided by an address registration daemon, ilmid.

ATM Address Registration Daemon (ilmid)

Address registration with a switch is controlled by ilmid. When an ATM interface is brought up at boot time, ilmid is also started. ilmid then begins an exchange of messages with the switch: relaying local address information (the 7 octet ESI and selector) to the switch and receiving the 13 octet network prefix information from the switch.

The default local address that is registered with the switch at boot time consists of the network prefix provided by the switch, the MAC address assigned to the local interface, and the default selector for that interface (usually 0). Additional addresses are registered in two different ways. aarsetup(1M) and lanesetup(1M) register additional local addresses that may appear in aarconfig(4) and laneconfig(4), respectively. You can also use atmreg(1M) to register addresses, un-register addresses, and check the status of any address.