Networks Analyzed @ Netralized

After configuring your switch with Vlans you notice that something is wrong.

I will give you a simple guide to troubleshoot Vlans and make things work again.

• First check for Layer 1 and Layer 2 issues
• Is the cable plugged into the correct port?
• Is the link light on, and if so, what color is it? (If the led has a green color, it means that the switch port is in the forwarding state, if the port led has a yellow color the port is in the blocking state and if the port has a yellow blinking led, it is in the error state.
• We can use the Switch# show interface command to confirm link state
• Check the duplex mode

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Voice over IP (VoIP) is a major networking application and nowadays is appearing everywhere. VoIP is running over common high speed connections as: Ethernet, Frame Relay, ISDN, ATM, DSL, Cable and other.

With the VoIP technology we can transmit the analog voice signals of our telephone, through the traditional data network. This technology works by encoding analog voice signals into IP packets. These packets are sent across the data network and reassembled and decoded at the other end back to analog signal.

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If you want to discover all the active hosts on your subnet from your routers console, you can perform a ping in the broadcast address of your subnet. Keep in mind that all the active nodes on your subnet should respond to that ping. As a tip I can tell you that this kind of ping will only work in privileged exec mode.

For example if you use the subnet 10.1.1.0 /24 the broadcast address is 10.1.1.255

From privileged mode perform a ping like this:

Router#ping 10.1.1.255

A “list” with all the active nodes should appear.

Another command that you can use to find out with witch hosts has the router communicated is

Router#show ip arp

You can use this useful type of ping for many types of things, for example to check how many computers are connected on a wireless network. Till our next article, stay tuned.

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Many times a lot of us who use laptops or desktop computers which are equipped with wireless network cards, have tried to scan an area for available wireless access points. We usually use the default wireless network scanner of the Windows operating system.

But is this the most efficient tool for this job?

Surely not.

There is a tool, not quite widespread, called Network Stumbler which is much more effective than the default windows scanner. The network stumbler is a wireless network scanner that supports many different chipsets of wireless network cards as Lucent, Dell True Mobile, Compaq WL 110, Elsa Airlancer and several others.

I guess that many of you are already familiar with it. For those who haven’t heard of it before let’s see why network stumbler is better than the default windows wireless scanner.

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Accessing remote network devices for monitoring purposes or for configuring it, is an everyday activity of any network administrator.

But which remote access method you use?

Maybe telnet is a good idea if you don’t care about security.

Always keep in mind that using telnet to communicate with your remote network devices is not secure because all the traffic that passes through the telnet session is sent unencrypted. Saying all the traffic includes also your passwords. This means that anyone who can eavesdrop your data can easily find your password.

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After Lebyathans comment in the article “understanding ip addressing“, I have decided to give you an example of subnetting using the ip and subnet mask he mentioned. In this article you can see how we can find the network address, first valid host, last valid host, broadcast address, number of subnets and number of hosts in our network.

The Ip address is 192.168.5.33 and the mask is /27

First translate the mask from /27 to decimal form. /27 means 27 continuous 1’s in binary. It looks like this 11111111.11111111.11111111.11100000 and if we do the conversion to decimal the result is 255.255.255.224

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Setup and configuration of a home wireless network is not a very difficult task. Although, we need the appropriate devices and some basic knowledge. All the devices that will connect to the wireless network must have a wireless network card. Usually laptops and PDAs have the wireless card on-board or if they don’t, we can add a network card attaching it to a PCMCIA slot.

For desktop computers we can install a network card using a PCI slot or we can use the USB port. USB network cards have become very popular because it’s very easy to install them to PCs.

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Ip addresses consist of two parts, Network and Host part. Take for example the Ip address 172.16.1.1

What is the Network part and what is the Host part of an Ip address?

You can’t tell before assigning a subnet mask for the specific Ip address. By using a subnet mask we can distinguish the network and the host portion of the Ip address. The 255 part of the mask shows the network and the 0 part shows the host.

When we are given an Ip address and a subnet mask, we can discover the network address, the broadcast address, the first valid host Ip address and the last valid host Ip address of our network.

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VPN (virtual private network) is a tunneling method that gives us the capability to connect two remote sites together over the public WAN.

VPN allows us to connect to our local network from remote locations. For example let’s say that we have a company with two sites, one central office in California and one branch office in Texas. Some of the available methods for establishing a connection between them are: leased line, frame relay and ATM. But from the cost point of view none of these methods has the efficiency of VPN tunnels. You can establish a VPN tunnel even by using a cheap DSL connection.

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Ip addressing is a vital knowledge for all the IT and non IT people that are involved with networks, from large enterprise networks to small home networks.

To fully understand Ip addressing it’s necessary to be familiar with binary mathematics and conversions, from the decimal mathematic system to binary and vise versa. I will try to present you an easy procedure that can be used when doing conversions.

Binary to decimal

Binary numbers that are associated with Ip addressing always have eight digits (I like to call these digits “spaces”).
For example the number 11010101 as you can see is an eight digit number.
Now let’s try to convert this number into decimal:

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