Simple Network Management Protocol (Snmp)

Network management software can manage devices from different manufacturers, it is necessary to standardize network management protocols. Currently there are some commonly used protocols such as:

o Simple Network Management Protocol (SNMP)

o Remote Monitoring Network Protocol (RMON)

8.3 Simple Network Management Protocol (SNMP)

8.3.1 Introduction

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SNMP is an application-layer protocol that is defined to facilitate the exchange of management information between devices. SNMP is considered as a part of the TCP/IP protocol suite. It allows network administrators to monitor network performance, find and solve network problems, and plan for network expansion.

SNMP has two versions, SNMP v.1 (RFC1157) and SNMP v.2 (RFC1902). Both have some common features. However, SNMP v.2 provides more advanced features, as well as adding more tasks to the protocol. The third version is not yet standardized.

According to SNMP, a network management system consists of basic components such as: Managed device, agent and Network Management System.


Figure 8.2 – Architecture of the network management system according to SNMP

8.3.2 Basic commands in SNMP protocol

Devices are monitored and controlled using four basic commands supported by the SNMP protocol: read, write, trap, and reverse operations.

o The read command is used by an NMS to monitor managed devices. The NMS examines various parameters stored by the managed device.

o The write command is used by an NMS to control managed devices. The NMS changes the values ​​of parameters stored on the managed device.

o The trap command is used by managed devices to signal to the NMS any unusual events it detects.

o Traversal operation is used by NMS to determine which parameters are supported by a managed device and thereby gather the information in tables.

8.3.3 SNMP management information base

MIB is a collection of information organized in a hierarchical manner. MIB is accessed using network management protocols such as SNMP. MIB contains information about managed objects as objects, and each object is identified by an identification number.

A managed object in MIB (sometimes called a MIB object) is one of the characteristic attributes of a managed device. Managed objects consist of one or more object instances, usually variables.

There are two types of managed objects: scalar objects and tubular objects. Scalar objects define a single instance of an object. Tubular objects define multiple instances of related objects and these are grouped into tables in the MIB.

An example of a managed object is the amount of packets entering an interface on a router. This is a scalar object because its value is just an integer.

An object identifier uniquely identifies a managed object within the MIB hierarchy. The MIB hierarchy can be described as a tree whose root has no label and whose levels are assigned to different organizations.


Figure 8.3 – General registration tree

The identifiers of the first level objects belong to different standardization organizations. While the lower levels are assigned by the corresponding organizations at the upper level. Manufacturers can define their own branches to define the managed objects on their own products. MIB is not standardized yet so it is placed in the experimental branch.

For example, the managed object atInput is located at the path described in name form as: « iso.IDentified- organization.dod.internet.private.enterprise.cisco.temporaryvariables.AppleTalk.atInput » or in numeric form as the string « 1.3.6.1.4.1.9.3.3.1 ».


Chapter 9

LAN local area network design

Purpose

This chapter aims to introduce the reader to the following issues:

LAN design process

Create LAN design diagram

Physical layer network diagram

Connect layer 2 with switch

Network design at layer 3

Determine the location of the Server

How to make documents, network profiles


9.1 Introduction to LAN design process

One of the most important steps in ensuring a fast and stable network is network design. If a network is not designed properly, many unforeseen problems will arise and the network may become unstable as it expands. Network design includes the following processes:

o Collect information about the needs and desires of network users.

o Identify current and future data flows with an eye toward future growth and server placement.

o Identify all layer 1,2 and 3 devices required for LAN and WAN network diagrams.

o Document network installation at physical and logical levels.

There will be multiple design solutions for the same network. Network design needs to be oriented towards

to the following goals:

o Operational capability: The first criterion is that the network must operate. The network must meet the user's work requirements, must provide connectivity between users, between users and applications with an acceptable speed and reliability.

o Scalability: The network must be scalable. The initial design must be scalable without causing any major changes in the overall design.

o Compatibility: The network must be designed with a pair of faces always facing new technologies and must ensure that it does not prevent the introduction of new technologies in the future.

o Manageable: The network must be designed to be easy to monitor and administer to ensure smooth operation of the features.

This chapter focuses primarily on the network design process and documentation issues.

9.2 Create a network design diagram

Once the requirements for an overall network have been gathered, the next step is to build a network topology or model of the network that needs to be established. The design of a network topology is divided into three steps:

o Design network diagram at physical layer

o Design network diagram at data link layer

o Design network diagrams at the network layer.

9.2.1 Developing a physical layer network diagram

The wiring diagram is one of the issues that must be considered when designing a network. Design issues at this level involve the choice of cable type to be used, the cable routing must satisfy the bandwidth and geographical constraints of the network.

Star network topology using CAT 5 twisted pair cable is commonly used today. For small networks, only one central connection point is needed for all computers provided that the distance from the computer to the central connection point is no more than 100 meters.

Normally, in a building, people choose a special room to install network devices such as Hub, switch, router or patch panels. People call this room MDF (Main distribution facility).


Figure 9.1 – Using MDF for networks with diameters less than 200 meters

For small networks with only one centralized connection point, the MDF will include one or more horizontal cross connect patch panels (HCC).


Figure 9.2 – Using HCC patch panel in MDF

The number of horizontal cables and the size of the HCC patch panel (number of ports) depend on the number of computers connected to the network.

When the distance from the computer to the connection hub is greater than 100 meters, more connection hubs are needed. The second level connection hub is called the Intermediate Distribution Facility (IDF). The cable connecting the IDF to the MDF is called vertical cabling.


Figure 9.3 – Using additional IDFs for networks larger than 200 meters in diameter

To connect IDFs to an MDF, additional vertical cross-connect patch panels (VCC) are required. The cable connecting two VCC patch panels is called vertical cabling. They can be twisted pair cables if the distance between the MDF and IDF is not greater than 100 meters. Otherwise, fiber optic cables must be used when the distance is greater than 100 meters. The speed of vertical cables is usually 100 Mbps or 1000 Mbps.


Figure 9.4 – Using VCC patch panel to connect IDF to MDF The product of this stage is a set of documents specifying the following information:

o Exact location of MDF and IDFs connection points.

o Type and quantity of cables used to connect the IDFs to the MDF


Figure 9.5 – Documentation of MDF and IDF locations

o The cable ends must be numbered and the connection between the ports on the HCC and VCC patch panel must be noted. The example below notes the information about the cables used at IDF No. 1.


Figure 9.6 – Wiring documentation at an IDF

9.2.2 Layer 2 connection using switch

Collision and collision zone size are two factors that affect network performance. By using switches we can segment the network, thereby reducing the frequency of collisions between computers and reducing the size of the collision zone in the network.

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