Thursday, 31 December 2009


First To Understand Voice VLAN

The voice VLAN feature enables you to configure a switch port ports to carry voice traffic from IP phone. When the switch is connected to a Cisco IP Phone, the phone sends voice traffic with Layer 3 IP precedence that give voice a priority on Data. Because the sound quality can be compromised if Data is being sent unevenly. and you need to configure a switch to trust the priority assigned by Cisco IP phone

The Cisco IP Phone contains an integrated 10/100 switch as shown below

So Connectivity would be something like this

Port 1 connects to the PoE Switch
Port 2 (access port) connects to a PC or other device.

Configuration and Tuning

After connectvity You need to configure an access port attached with Cisco IP Phone to carry voice through One VLAN and data traffic from another VLAN So here comes in play Cisco Discovery Protocol (CDP) packets that instruct an attached phone to send voice traffic to the switch in appropriate LAN  with IP Precedence priority Vlaue 

Default Layer 3 IP Precedence Value for Voice is 5 and 3 for Control  traffic

Note that Voice VLAN is only supported on access ports and not on trunk ports, though this configuration is allowed and no error is shown.

you must be careful that Voice Vlan exist on the Switch (by issuing th following Command in Exec Mode SHOW VLAN )before setting up the port for IP Phone.  I hope no one pops up and ask how to create Voice Vlan ... :)

You need to enable QoS on the switch ( mls qos ) and configure the port trust by entering (mls qos trust cos) so Switch interface will trust the CoS attached in Header 

IP Phone and a device attached to the phone cannot communicate if they are in the same VLAN and subnet but use different frame types because traffic in the same subnet is not routed 

So the final config will look like as Below :- 

Switch_A # config t

Switch_A(config)# interface gi 0/1

Switch_A(config-if)# mls qos trust cos         (Enable QOS and Trust the Value of CoS)

Switch_A(config-if)# switchport voice vlan dot1q

Friday, 18 December 2009

Network Management system

What is the Best NMS , What NMS to Go with , Which NMS is Best for my Organization ???????????

These are the questions wrecking your head when your organization decide to buy or move to any other NMS , here are some information I will put in and keep on updating it .

First and Foremost There is no specific network monitoring tool which can be said to be the best.. Hahaha I know what you guys are thinking at teh moemnt .

Most of them are preety good and provide you with the information you need on day to day basis.It actually depends upon what you are looking for in a monitoring tool like
  • COST ($$$$$) you are willing to pay
For a small network, you would do well with a small tool and even with open source, but for a bigger network you would naturally go for higher-end products.

  • Easy to use
Easy to use and can extract the reports or information you are looking for

Concord, HPOV, Unicenter TNG, Tivoli and SOlarwinds are some of the good tools that I have worked with.

Here are Some Pre Purchase checklist of NMS Applications , Normally these are the areas where NMS Vendors trick us ....

  • Root Cause Analysis
True Root cause analysis Means that your NMS is capable to Look through 1000 of events and point out the main cause of the problem . I.e if one router interface is the reasone of whole site failure then NMS should point out this interface is the main reasone that we cannot see any other device in remote office.Event corelation , component monitoring for critical arams are the key fac tors that help in adding real Root cause analysis capability in the NMS

Inorder to do root cause analysis NMS must have collected sufficient data about the networj beaviours and see which Devices are dependent on whihc one. Finally deviation or anomaty can help in proper root acuse analysis .
  • SNMP Capable..
Most NMS claim that there appliaction is SNMP capable. they dont mention they are only offering simple SNMP GET requests which only ask a network device to return the current value of a (OID), such as "Packets out" i.e 12000 and of corse you cannot do much with this information However Real NMS produces appropriate information by processiong values from IOD like Bandwidth utilization Normally using forula to calculate this

(Total Octates IN + total Octates OUT) * 8 / 1024 = Bandwidth

So be sure to check the whole process how NMS works with OID's and dont get screwed ... :) by puchasing only SNMP get based NMS

Q. Does ASA support SNMPv3?

A. Yes. Cisco ASA Software Release 8.2 supports Simple Network Management Protocol (SNMP) version 3, the newest version of SNMP, and adds authentication and privacy options in order to secure protocol operations.