Information Technology Reference
In-Depth Information
21
CHAPTER
Troubleshooting ATM LAN Emulation Networks
This chapter introduces general troubleshooting techniques related to LAN Emulation (LANE)
networks.
We will first briefly introduce LANE as it was conceived: a LAN technology aimed at emulating a legacy
Ethernet network over ATM. We will then cover troubleshooting of the most common problems using
this technology:
Troubleshooting LANE Clients not coming up
•
Troubleshooting LANE connectivity (after LANE Clients are up)
•
Introduction
LANE is a standard defined by the ATM Forum that provides ATM-attached stations the same
capabilities that they normally obtain from legacy Ethernet LANs. As the name suggests, the function
of the LANE protocol is to emulate a LAN on top of an ATM network. By making an ATM interface
look like one or more separate Ethernet interfaces, LANE enables LAN users to take advantage of ATM's
benefits without requiring modifications to end-station hardware or software.
ATM is a connection-oriented service that establishes connections between source and destination
devices. LAN-based protocols, on the other hand, are connectionless and use broadcasts so that source
devices can find one or more destination devices. The primary purpose of LANE, then, is to provide the
same services that a broadcast medium such as Ethernet does.
The LANE protocol resolves MAC addresses to ATM addresses so that LANE end systems can set up
direct connections between themselves and then can forward data. The LANE protocol can be deployed
in two types of ATM-attached equipment:
•
Hosts or routers with ATM network interface cards (NICs). ATM NICs implement the LANE
protocol and interface to the ATM network while presenting the current Ethernet service interface
to the higher-level protocol drivers. The network layer protocols continue to communicate as if they
were on an Ethernet by using known procedures. However, they are capable of taking advantage of
most of the advanced services of the ATM network.
•
The second class of network device that implements LANE consists of ATM-attached LAN switches
and routers. These devices, together with directly attached ATM hosts equipped with ATM NICs,
are used to provide a virtual LAN service in which ports are assigned to particular virtual LANs,
independent of physical location.
The LANE specification defines several components that enable the protocol to provide the broadcast
and address resolution services required to emulate traditional LANs:
