### TechNote

Number: 03202-03
Date: October 1994

## HLM and SNMP

### Introduction

Many networks comprise a variety of multi-vendor hardware and software. Network managers need some form of software that:

- Monitors all the different components of the network, for example, servers, bridges, routers, and printers

- Is not specific to a particular vendor

- Provides management of the network from a single workstation

As a result, several network management protocols have emerged. This document discusses two of these: SNMP (Simple Network Management Protocol) and HLM (Heterogeneous LAN Management).

### Features in common

SNMP and HLM have three basic things in common:

1. Using ASN.1 to encode data:

   Abstract Syntax Notation One (ASN.1) is an ISO defined standard for encoding data on the network and is used by management protocols, such as SNMP and HLM, to encode the data.

2. Storing management information in a MIB:

   A Management Information Base (MIB) is a way of describing all the aspects of a device on the network. You can think of it as a database containing information about all the variables or parameters, associated with a device, which can be queried and/or changed.

3. Manipulating the MIB using a small set of commands

### Other features

Although SNMP and HLM have these three basic features in common, they also differ in several ways. The rest of this document briefly summarizes these two protocols.

### SNMP

SNMP is the principal management protocol used on Ethernet networks and has become a de facto standard for network management on Ethernet. However, it has not yet become established in IBM Token Ring environments.p

SNMP grew from work by the Department of Defense (DoD) and was first published in 1988. The standard is now administered by the Internet Activities Board (IAB) through the use of documents known as Request For Comments (RFCs).

SNMP is based on routable, connectionless protocols, traditionally the Internet Protocol (IP), although there is a move by Madge, Novell, and Hewlett-Packard to implement it over Novell IPX.

One major problem with SNMP is that it does not offer any significant network security. A version of SNMP known as "Secure SNMP" has been proposed, but this is not currently available as it requires a major redesign of SNMP. Companies that support SNMP include Madge, Sun, Hewlett-Packard, IBM, and Novell.

### HLM

HLM was defined more recently than SNMP and includes more sophisticated alert and security features. It was defined jointly by IBM and 3COM, and is based on ISO's CMIP (Common Management Information Protocol) standard. ISO CMIP is a layer-seven application in the ISO seven-layer reference model and, as a result, requires large amounts of personal-computer resources to implement in personal-computer network environments. HLM implements CMIP over a reduced ISO protocol stack, which enables it to run on personal computers. Since it was first introduced, HLM has been adopted by IEEE as the standard for LAN management. HLM requires a standard LLC interface. HLM offers the following advantages:

- It is a standard defined by an IEEE committee
- It offers powerful security features

IBM use HLM to manage the 8230 CAU intelligent wiring-concentrator. Madge have implemented HLM and SNMP in SmartCAU, which enables it to be managed in both IBM HLM environments and SNMP environments. Also, Madge extended HLM to work across IPX routers.