SNAP-DLSw

Summary

SNAP-DLSw is a high-performance implementation of DLSw version 1 and version 2 as defined by Informational RFC 1795 and Informational RFC 2166, providing full back-level compatibility with Informational RFC 1434. For more information on DLSw, please see our white paper.

SNAP-DLSw can also be used as the basis of an SNA Frame Relay Access Device (FRAD) using the encapsulation defined in Informational RFC 1490.

The key features supported by SNAP-DLSw include :

  • full mandatory support for DLSw Standard Version 1.0 as defined in Informational RFC 1795 including
    • separation of resource location from circuit establishment
    • initial capabilities exchange
    • adaptive flow-control and pacing for WAN data traffic
    • circuit level priority negotiation
    • largest frame size negotiation
  • full mandatory support for DLSw Standard Version 2.0 as defined in Informational RFC 2166 including
    • TCP connections on demand
    • address resolution through UDP
    • handling of vendor-specific SSP messages
    • NetBios broadcasts over UDP
  • High Performance Routing (HPR) support
  • flexible, dynamic configuration capabilities
  • advanced diagnostics (error logs, tracing, dumps)
  • provision of code exit procedures for vendor specific enhancements
  • interconnection of local and remote LANs (Token-ring or Ethernet) and/or SDLC devices via a TCP/IP WAN
  • locally switched interconnection of local LANs and/or SDLC devices
  • locally switched interconnection of Frame Relay and local LANs or SDLC devices
  • full back-level interoperation with the IBM 6611 MPNP R1.2 for SNA and NetBIOS traffic
  • provision of a "fast path" for all data frames
  • use of MAC address and NetBIOS name caches to reduce WAN explorer traffic
  • two-way flow control of the local node and the DLSw partner
  • local and remote MAC address and NetBIOS name filters
  • optionally disallowing connections from DLSw partners that have not been explicitly defined to SNAP-DLSw
  • support through the SOF QUERY interface for GET operations on the DLSw MIB
  • C coding throughout.

SNAP-DLSw is fully portable and makes very few assumptions about the underlying hardware or operating system. Portability to different operating environments is achieved using a mapping layer, called the N-BASE, to provide services such as scheduling and memory management. SNAP-DLSw and the N-BASE have been designed to perform well in both standard multi-threaded, single processor operating systems as well as more complex environments such as:

  • ultra high-performance single-threaded operating systems or sub-systems found at the heart of most router products
  • distributed environments with small high-speed data path processes and larger background management processes
  • symmetric or asymmetric multi-processor systems.


Compatibility

SNAP-DLSw uses the Extended SNAPS DLC Interface to obtain promiscuous LAN access. SNAP-DLSw interoperates with SNAP-LLC2 which is a provider of that interface.

SNAP-DLSw uses the non-extended SNAPS DLC interface to obtain access to SDLC devices. SNAP-DLSw interoperates with SNAP-LINK which is a provider of that interface.

SNAP-DLSw also provides the non-extended SNAPS DLC Interface for use by local applications. SNAP-DLSw interoperates with SNAP APPN as the local application.


Local DLC Support

In addition to providing switching between a WAN (normally TCP/IP) and a LAN (LLC2) or SDLC device, SNAP-DLSw also allows local applications to be the logical end-point of a circuit.

If the logical end-point for a circuit is a local application running on the node on which SNAP-DLSw itself is running, SNAP-DLSw will establish the connection and exchange DLC_MU messages with the application (typically SNAP APPN) directly. In such cases, SNAP APPN is effectively placed on the DLSw virtual ring and can be accessed by remote DLSw providers via TCP/IP.

The diagrams below contrast circuits to LAN-connected, SDLC-connected and local users of SNAP-DLSw.

Circuit including LAN point
Circuit including LAN end-point

When a circuit has a LAN end-point, SNAP-DLSw routes frames between TCP/IP and the DLC providers using the Extended SNAPS DLC Interface to obtain the promiscuous LAN access required for DLSw.

Circuit including SDLC device end-point
Circuit including SDLC device end-point

DLSw circuit with local end-point
DLSw circuit with local end-point

When a circuit has a local application, such as SNAP APPN, as the end-point, SNAP-DLSw routes frames between TCP/IP and the application using the SNAPS DLC interface to exchange frames with the application.


Local Switching Support

SNAP-DLSw also provides the ability to perform local switching. Local switching allows the following features to be built into the switch :

  • interconnection of local TCP/IP or Token-Ring LANs
  • connection of local SDLC devices to applications running on local LANs
  • connection of local LANs and/or SDLC devices to Frame Relay (FRAD).

When performing local switching, SNAP-DLSw establishes direct data paths between the two DLC providers for maximum throughput.

The diagrams below show an example circuit involving local switching and an example FRAD circuit. These diagrams should be contrasted to the circuits given above where only one of the end-points is local.

DLSw circuit showing local switching between SDLC and LAN
DLSw circuit showing local switching between SDLC and LAN

DLSw circuit showing use as an SNA FRAD
DLSw circuit showing use as an SNA FRAD


Management and Statistics

SNAP-DLSw is managed via the Switch Operator Facility (SOF) API. This provides a fully dynamic configuration facility for SNAP-DLSw and allows access to the circuit, filter and DLSw partner tables for the implementation of a SNMP MIB agent for SNAP-DLSw.

SNAP-DLSw does not keep circuit-level statistics but provides SOF commands to access the statistics maintained by the underlying DLC providers, such as SNAP-LLC2 or SNAP-LINK.


SNAP-DLSw Deliverables

SNAP-DLSw is delivered as a set of C source modules. The delivered code is as follows.

  • SNAP-DLSw product code (30,500 lines of code)
  • Sample SST stub (2000 lines of code)
  • SNAPS Product Support Library (4,500 lines of code)
  • Sample N-BASE (7,500 lines of code).

A set of test scripts is provided to help you validate that you have ported and installed SNAP-DLSw correctly. The scripts are written to run in the N-BASE testbed which you must also port to your environment. All of the tests run in the sample portable N-BASE, which contains a testbed.

The following documents accompany SNAP-DLSw.

  • SNAP-DLSw SST Interface Specification
  • SNAP-DLSw SOF Interface Specification
  • SNAP-DLSw Problem Determination Guide
  • SNAP-DLSw Product Overview
  • SNAP-DLSw Architecture Guide

For more information about SNAP-DLSw, contact .