RFC 1538 (rfc1538) - Page 2 of 10
Advanced SNA/IP : A Simple SNA Transport Protocol
Alternative Format: Original Text Document
RFC 1538 Advanced SNA/IP October 1993
1. Introduction
Advanced SNA/IP suggests a method for the transmission of SNA session
data over an IP network. This memo documents the SNA/IP protocol as
implemented in the McDATA LinkMaster(R) 6200 Network Gateway, McDATA
LinkMaster(R) 7100 Network Controller, and I/O Concepts X-Direct
TN3270 Server.
Advanced SNA/IP differs from other protocols designed to enable
routing of SNA session traffic over an IP network. SNA/IP was
originally designed for implementation in peripheral network nodes
like SNA gateways and downstream nodes (DSNs). It is the authors'
view, however, that SNA/IP could also be implemented in intermediate
network nodes like routers as the base for an LLC to IP subnet
gateway or data link switch function.
2. Motivation and Rationale
The token-ring media access control (MAC) protocol 802.5 and logical
link control (LLC) protocol 802.2 were the first set of LAN protocols
used to provide a reliable and connection-oriented data link service
for SNA sessions in a LAN environment.
McDATA's experience with transporting SNA over 802.5 networks led to
an 802.3/802.2 (Ethernet) based variation. As prospective customers
were introduced to these Ethernet products, the question of
routability arose. Network administrators, accustomed to working
with Ethernet networks and the IP-based protocols, required an IP
routable solution. McDATA's "SNA over Ethernet" products were
bridgeable, but were not routable.
SNA sessions require a reliable and connection-oriented data link.
TCP running over IP provides a reliable and connection-oriented
transport service and has the added benefit of being routable. It
seemed the UDP and TCP protocols could be used in place of 802.2 Type
I and Type II levels of service used in traditional SNA token-ring
implementations. Advanced SNA/IP was created as a result of these
observations.
Behl, Sterling & Teskey