Oracle for Unix - I


Found usually in /etc or /var/opt/oracle.

oratab is used by ORACLE utilities. It is created by the root.sh script (a part of Oracle installer), and is updated by the Database Configuration Assistant when creating a database.

Entries in this file have the following format:

A colon, ':', is used as the field terminator. A new line terminates the entry. Lines beginning with a pound sign, '#', are comments.

The first and second fields are the system identifier and home directory of the database respectively. The third filed indicates to the dbstart utility that the database should , "Y", or should not, "N", be brought up at system boot time.

List all installed Oracle products

For Oracle 8i and above:
cd $ORACLE_HOME/install
cat unix.rgs

Verify Oracle installation

select host_name, instance_name, version, status from v$instance;

TNS-12542: TNS:address already in use

Check if the TNS port is not already in use by another Oracle instance.
  1. Check if the host name specified in listener.ora is correct.
  2. Do a netstat - a to check if any other application is using the port specified in listener.ora
  3. If the listener.ora has been copied from somewhere (samples or elsewhere), check the ORACLE_HOME

Set the Listener Process for Automatic Startup

Edit /var/opt/oracle/lsnrtab, and change/add a line containing the name of your listener (as specified in listener.ora and change the start-up value to "Y")


Cisco SAA

The Cisco Service Assurance Agent (SAA) is a Cisco IOS feature that allows users to monitor network performance between a Cisco router and a remote device (which can be another Cisco router, an IP Host or an MVS host). Performance can be measured for real world scenarios through the configuration of SAA operations that are executed periodically. Metrics measured include round trip response time, connect time, packet loss, application performance, inter-packet delay variance ( jitter), and more.

The SAA Support for Frame Relay, VoIP, and MPLS VPNs feature enhances the functionality of the Cisco SAA network monitoring solution as follows:

  • SAA Frame Relay - operations allow the user to monitor key performance metrics (round trip latency, packet loss, and data integrity) over Frame Relay permanent virtual circuits (PVCs).
  • With VPN Awareness, SAA allows monitoring within Multiprotocol Label Switching (MPLS) Virtual Private Networks (VPNs), enabling service providers to plan, provision, and manage IP VPN services according to the service level agreement (SLA) for a customer.


  • Frame Relay Monitoring - The SAA Frame Relay operation allows users to measure parameters such as response time (round trip latency), frame loss, and data integrity over frame relay circuits (PVCs). By measuring these parameters, providers can verify if the protocol is working correctly to meet customer needs.
  • Path Jitter Monitoring for VoIP Networks - The SAA Path Jitter operation allows the monitoring of interpacket-delay-variance a hop by hop basis. The Path Jitter operation provides measurements not only for jitter, but for other parameters such as response time, packet loss. The ability to monitor jitter is a key performance metric for VoIP networks. By using this operation, providers can monitor the performance of different paths in the VoIP network to insure Voice transmission quality for customers.
  • MPLS VPN Monitoring (VPN Awareness) - This enhancement to the SAA allows users to launch SAA operations on an MPLS VPN PE router. Being able to launch SAA operations allows providers to plan, provision, and manage IP VPN services according to the SLA for their customers. VPN Awareness means that montoring can be performed for a specific VPN by specifying a VPN routing/forwarding (VRF) name.


  1. Cisco SAA Support for Frame Relay, VoIP, and MPLS VPN Monitoring
  2. Network Performance Management with Cisco SAA
  3. Cisco Systems Service Assurance Agent (SAA) (pdf)

Categories: , , ,


Layer 2, 3 and 4 switching

OSI LayerPhysical
7-ApplicationApplicaton Software

LAN-Compatible Software
E-Mail, Diagnostics, Word Processing, Database

Network Applications
Conversion Utilities
Vendor-Specific Network Shells and Gateway™ Workstation Software
5-SessionNetwork Operating SystemSPXNetBIOSDECnet™TCP/IPAppleTalk®
4-TransportNovell® NetWare® IPX™PC LANLAN MgrDECnetPC/TCP®VINES™NFSTOPS®Apple
3-Network Control
1-PhysicalE=Ethernet; TR=Token Ring; A=ARCNET®; P=PhoneNET®

Layer 2 (data-link) Switching

Layer 2 switches use the MAC address, and are very fast since they are just sorting physical addresses.

If the layer 2 switch does not know where to send its frame, it broadcasts the frame from all its ports to the network to learn the correct destination. When the frame's reply is returned, the switch learns the location of the new address and adds the information to the switching table.

Layer3 addresses are determined by the equipment manufacturer.

Layer 3 (Network) Switching

Layer 3 switches use the network or IP address, and are capable to identifying the network locations as well as the physical address. A location can be a LAN workstation, or even a location within the computer's memory (port)

Layer 3 switches are smarter than layer2 devices incorporating routing functions to calculate the best path for delivering packets, however; they are not as fast as the layer2 switches.

Layer3 addresses are determined by the network administrator.

Layer 4 (Transport) Switching

Layer4 switches make use of the application protocols (HTTP, FTP, etc) to deliver the packets to appropriate application software, thus making decisions based not only on the MAC or the IP address, but the application a packet is targeted to

Layer4 switches allow for priorities to be established for network traffic based on application.

Implications of layer2 and layer3 switching

Although layer2 switches use microsegmentation to satisfy the demands for more bandwidth and increased performance, network designers are now faced with increasing demands for intersubnet communication. Every time a user accesses servers and other resources which are located on different subnets, the traffic must go through a Layer3 device.


MPLS is an IETF initiative that integrates Layer 2 information about network links (bandwidth, latency, utilization) into Layer 3 (IP) within a particular autonomous system--or ISP--in order to simplify and improve IP-packet exchange.

MPLS gives network operators a great deal of flexibility to divert and route traffic around link failures, congestion, and bottlenecks.

From a QoS standpoint, ISPs will better be able to manage different kinds of data streams based on priority and service plan. For instance, those who subscribe to a premium service plan, or those who receive a lot of streaming media or high-bandwidth content can see minimal latency and packet loss.

When packets enter a MPLS-based network, Label Edge Routers (LERs) give them a label (identifier). These labels not only contain information based on the routing table entry (i.e., destination, bandwidth, delay, and other metrics), but also refer to the IP header field (source IP address), Layer 4 socket number information, and differentiated service. Once this classification is complete and mapped, different packets are assigned to corresponding Labeled Switch Paths (LSPs), where Label Switch Routers (LSRs) place outgoing labels on the packets.

With these LSPs, network operators can divert and route traffic based on data-stream type and Internet-access customer.