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65
CHAPTER
7
Classical IP and LAN Emulation
Protocols
This chapter describes ATM protocols and how they are supported by the SunATM
software. This chapter is composed of the following sections:
■ “ATM Network Protocols” on page 65
■ “ATM Addresses and Address Registration” on page 66
■ “Classical Internet Protocol” on page 67
■ “LAN Emulation” on page 69
ATM Network Protocols
ATM is 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 differences in 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
ATM Forum. 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 ATM interface. Thus IP itself
sees the ATM interface just as it sees any traditional network interface. Every
SunATM interface 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 ATM modules, the plumb and
unplumb options of ifconfig will not work on ATM interfaces. The
atmifconfig(1M) command may be used to plumb and unplumb ATM interfaces.
IP treats the ATM interface as a subnet, choosing the interface used to send a packet
out based on the IP address of the destination and on the IP address and netmask of
the interface itself.