65
CHAPTER 7
Classical IP and LAN EmulationProtocols
This chapter describes ATMprotocols and how they are supported by the SunATM
software. This chapter is composed of the following sections:
■“ATMNetwork Protocols” on page 65
■“ATMAddresses and Address Registration” on page 66
■“Classical Internet Protocol” on page 67
■“LAN Emulation” on page 69

ATM Network Protocols

ATMis a connection-oriented network protocol, which means that a connection
must be established between two communicating entities before data transfer can
begin. IP is inherently connectionless. The implementation on the host must
therefore reconcile the differencesin these two paradigms.
There are two standard ways of doing this: Classical IP,standardized in RFC 1577,
and LAN Emulation, standardized in the LAN Emulation 1.0 specification from the
ATMForum. The SunATM architecture supports both of these methods. This chapter
discusses some of the key ideas of these two methods.
Both methods allow IP to run transparently over the ATMinterface. Thus IP itself
sees the ATMinterface just as it sees any traditional network interface. Every
SunATMinterface has a subnet IP address. As an ATM interface starts up,
appropriate modules and drivers are plumbed. All the TCP/IP and
UDP/IP applications run without modifications over these modules, and all the
utilities associated with the network interfaces also run without modification and
display similar results (for example, netstat and ifconfig utilities), with one
exception. Because of the different plumbing of the ATMmodules, the plumb and
unplumb options of ifconfig will not work on ATMinterfaces. The
atmifconfig(1M) command may be used to plumb and unplumb ATMinterfaces.
IP treats the ATMinterface as a subnet, choosing the interface used to send a packet
out based on the IP address of the destination and on the IP addressand netmask of
the interface itself.