TFTP Server for Newbies

TFTP or Trivial File Transfer Protocol can be a very useful network management tool. Although it's a simplified version of FTP, but because of that simplicity it wins the heart of all network engineers.


You can use TFTP server for numerous purposes when relating it with network devices.
You can use it for uploading or downloading Cisco IOS or other network vendors' operating systems, backup configuration files, or even run firmwares or operating system over the network for IP Phones, network devices, etc. without storing them in the devices.

I think most if not all of the professionally managed networks are definitely using TFTP servers.

I quoted from wikipedia about the details and features of TFTP Servers:

• It uses UDP port 69 as its transport protocol (unlike FTP which uses TCP port 21).
• It cannot list directory contents.
• It has no authentication or encryption mechanisms.
• It is used to read files from, or write files to, a remote server.
• It supports three different transfer modes, "netascii", "octet" and "mail", with the first two corresponding to the "ASCII" and "image" (binary) modes of the FTP protocol; the third is obsoleted by RFC1350.
• The original protocol has a file size limit of 32 MB, although this was extended when RFC 2347 introduced option negotiation, which was used in RFC 2348 to introduce block-size negotiation in 1998 (allowing a maximum of 4 GB and potentially higher throughput). If the server and client support block number wraparound, file size is essentially unlimited.
• Since TFTP utilizes UDP, it has to supply its own transport and session support. Each file transferred via TFTP constitutes an independent exchange. That transfer is performed in lock-step, with only one packet (either a block of data, or an 'acknowledgement') ever in flight on the network at any time. Due to this lack of windowing, TFTP provides low throughput over high latency links.
• Due to the lack of security, it is dangerous over the open Internet. Thus, TFTP is generally only used on private, local networks.

You can find many free TFTP servers in the internet, most popular ones are:

WinAgents TFTP Server
TFTPD32
SolarWinds TFTP Server
Kiwi CatTools - Network tools collection including TFTP Server

Personally I use the SolarWinds TFTP Server, don't get me wrong, every TFTP server you can find is easy to install and configure. I just use the one from SolarWinds because I have been using it from a very long time ago.

Up there in the post is the image of SolarWinds TFTP server when I used it to upload IOS image for recovery.

To use a TFTP server is fairly easy, just make sure your router can reach the computer you use for TFTP server, run the TFTP service in your computer, provide a space for placing your files to upload or download, and run the copy command from the router.

Read more!

Cisco Device Bootup Steps

To understand how to configure routers is very important, but it's also important to understand what steps are involved when a Cisco router/switch is booting up.

This knowledge can help you get to know your Cisco devices better, plus there are questions related to the boot up steps in the CCNA exam.

First, we know that Cisco router is using IOS or Internetworking Operating System, which is a software that controls all the routing and switching functions in a Cisco network device.

There are some steps need to be done before loading the Cisco IOS and get your router/switch up and running.

1. Do POST

When first turned on, the cisco device performs POST or Power-On Self Test that executes diagnostics from the ROM on all hardware modules in the device.
It will verify all the basic operations of CPU, memory, and interface ports.

2. Loading the Bootstrap

Before loading the IOS to the RAM, Cisco device loads the bootstrap first. Bootstrap is a simple set of instructions that tests hardware and then initializes the IOS for operation.
Bootstrap is located at the device's ROM.

At this point, your console terminal will show you the following text, but the text will vary depends on the device you're using, interfaces available, and version of the IOS.

System Bootstrap, Version 11.3(2)XA4, RELEASE SOFTWARE (fc1)
Copyright (c) 1999 by cisco Systems, Inc.
TAC:Home:SW:IOS:Specials for info
C2600 platform with 24576 Kbytes of main memory

There you can see I'm using Cisco 2600 series router with IOS version 11.3(2), and you can see also the available RAM/DRAM.

After this information show up, you might also see the statement:

NVRAM invalid, possibly due to write erase

The above statement might show up if you're bought used Cisco device, don't worry it's not a malfunction or anything.
It only tells us that this router has not been configured yet or that the NVRAM has been erased, just do some configuration and save it, then the statement will go away.

3. Loading the IOS

After finished with the bootstrap, the device will try to search for the valid IOS.
You can place the IOS on a number of places and the device will search the IOS based on the configuration register. The default value of the configuration register is 0x2102 which tells the device to load the IOS from the flash memory.

The normal place for an IOS is the flash memory of the device, but you can also place the IOS on other network devices and load them through TFTP.
The console terminal then shows the decompression process of the image:

program load complete, entry point: 0x80008000, size: 0x2f8558
Self decompressing the image : ###############################################
###############################################
###############################################
###############################################
###############################################
################################## [OK]

Depending on the size of the IOS image, you'd get a longer # mark. I've work with the high end Cisco devices such as Catalyst 6500 series and it takes a quite long time to decompress the image, some of the image size could take more than 100Mb.

If after five attempts a valid IOS image is not found, the router will take you to the ROM mode (ROMMON).
More on ROMMON on the next post.

After the device found the IOS, it will load it to the RAM where it stays there as long as the router is on and lists all the available hardware and software in the router and show them to the console terminal screen.

Cisco Internetwork Operating System Software
IOS (tm) C2600 Software (C2600-I-M), Version 11.3(9)T, RELEASE SOFTWARE (fc1)
Copyright (c) 1986-1999 by cisco Systems, Inc.
Compiled Wed 07-Apr-99 15:43 by pwade
Image text-base: 0x80008084, data-base: 0x80564C88

cisco 2611 (MPC860) processor (revision 0x202) with 18432K/6144K bytes of memory.
Processor board ID JAB0317052N (1135645455)
M860 processor: part number 0, mask 49
Bridging software.
X.25 software, Version 3.0.0.
2 Ethernet/IEEE 802.3 interface(s)
1 Serial network interface(s)
32K bytes of non-volatile configuration memory.
8192K bytes of processor board System flash (Read/Write)

4. Load the Configuration File

Next step is to load the configuration file. The device will start looking the configuration file in the NVRAM, loads them to the RAM and executes them one line at a time.
The configuration file tells the router of the configuration you've done to it such as routing, ip addresses of the interface ports, etc.

If the device can't find the configuration file in the NVRAM, such case can be found when you freshly configure the device, it will try to search the available TFTP server in your network.
If no TFTP server found, it will then display the setup dialog on the console terminal screen.

Would you like to enter the initial configuration dialog? [yes] :

The option enclosed in the brackets [ ], shows the default option, you can just press enter to answer yes or type no to enter the configuration manually.

That's it, four bootup processes that you can easily remember. In CCNA exam, you'd probably be asked on these steps, what will the device do when can't find something here, and what it'll try next, etc.

There are some terminologies you should be familiar with, those are:

ROM - a read only memory that holds the bootstrap of the device and a limited version of Cisco IOS to run a very limited functions usually used for recovery and update.

RAM/DRAM - a volatile memory which will be deleted whenever the device is rebooted or shutdown,
RAM is used to hold the running IOS and the running configuration of the device.

NVRAM - a non-volatile memory which will not be deleted even if the device is rebooted or shutdown,
NVRAM is used to hold the saved configuration (startup configuration) which will be loaded when system bootup to the RAM.

Flash - Also a non-volatile memory used to store the IOS. On higher end Cisco devices, the flash memory is external, pretty much like memory you used for your digital camera (SIMM or PCMCIA).
Very convinient since you can upgrade it as you need.

TFTP Server - Trivial File Transfer Protocol, a simplified version of FTP that you can use to transfer file over the network.

ROMMON - More on this on the next post

Read more!

GNS3: Simulator for Your CCNA Exam

When pursuing for the CCNA title, you need to get yourself familiar with the Cisco devices, at least you have tried typing in some commands to configure the Cisco devices.

With a very limited budget, I'm sure it'll be very hard to buy your own Cisco routers and switches, although the prices are quite cheap these days on ebay.

To get around this problem you can use many Cisco simulators that are available out there, one of my favorite is the GNS3.

One problem I found with other simulators is that they don't support all of the commands in the Cisco devices, the GNS3 provides all of them since it is using a real Cisco IOS - the operating system of Cisco devices.

The only drawbacks using GNS3 are:

1. You have to have your own IOS, it's not provided for free from Cisco.
2. It can't simulate switch due to the ASIC hardware used by Cisco switches, but you can use router modules provided by the GNS3 to simulate switches using routers.
   
3. You have to tweak the simulator since it is simulating Cisco devices real time in your PC, it can eat up quite a lot of the PC processor and memory. No worry, you can find how to tweak the simulator in the provided manual from GNS3.

Other than the drawbacks, this simulator is awesome, it's like having your own Cisco devices to play with. Here is the sample of GNS3 interface:

There you can see you can add as many devices as your PC hardware allows, and you can access them through your command prompt telnet function to do the configuration.

Words of note, you can use command prompt telnet function if you use windows XP but in Vista you can't. The reason is Vista doesn't provide telnet function anymore so you have to download third party software for this, many are free by the way.

The coolest function of GNS3 is that if you're connected to the internet, you can simulate your NIC to provide internet connection to GNS3.

You can try configuring internet connection to the routers and test by pinging real live public internet addresses to see if you configure the connection correctly.

You can also install the GNS3 on several PCs and let the simulated routers communicate between the PCs, you can ping between the routers on different GNS3 simulators, and other function too, to keep the processing and memory requirements low, cool.

Read more!

TCP and UDP

If you're aiming for the CCNA exam, you definitely have to know about the TCP and UDP protocols. TCP and UDP are protocols that are running on the layer 4 / Host to Host layer / Transport Layer of the OSI Layer.

TCP (Transmission Control Protocol) is what you can say reliable protocol, it numbers each segments that are sent and wait for acknowledgment from the receiving side, when received at the end, the transport layer at that end will assemble the segments and deliver them to the upper layers.

This protocol is said to be connection oriented, it creates a virtual circuit which is a path between the source and destination.
Think of it like making a call, first you pick up the handset and dial a number, this will establish a path and maintain that path until you hung up the phone, same cronology happens at the network world.

Here is what TCP segment format looks like:

In typical CCNA exam question, you'd be asked to differentiate between TCP and UDP segment format, you don't need to remember all the fields up there, after seeing the UDP segment format you'll easily differentiate between TCP and UDP segment format.

UDP (User Datagram Protocol) is a connectionless protocol, it sends all segments to the network without have to wait acknowledgment from the destination host.
There are many reasons to use the UDP, for example in the SNMP used to monitor the network. The SNMP would constantly send messages to update the current status of network devices, using UDP would conserve your bandwidth because the format of the UDP, not to mention if you have to wait acknowledgment for every message you send.

Here is the UDP segment format:

 

Now you know how you can easily differentiate between the TCP and UDP segment format, the UDP has less fields. You can also understand why UDP can conserve the bandwidth in your network.

In my opinion, CCNA exam is a very fair exam, they won't try to trick you by adding false fields in the format, you just need to remember that the UDP segment format has lesser fields than the TCP format.

Related to the CCNA exam also, you need to know which application ports belong to the TCP and which are the UDP's. In some cases, an application would use both protocols such as DHCP.

Read more!

How Network Devices Communicate

Getting to know a little deep about how the network devices communicate in your LAN can be quite handy, especially if you're going to take the CCNA exam.

You can find many questions related to the how network devices communicate, what data unit they're using. You have to remember the data unit related to each layer in the OSI Layers.

From the upper layer generate the data, the transport layer turn this data into segments, the network layer divide them into packets, data link layer then divide again into frames, and lastly the physical layer will handle the bits.
You need to be familiar how each device treats the data unit.

Here is the typical question you'd get in the CCNA exam, look at the below picture:

As a network admin you have the above network diagram, you have 2 networks, 192.168.1.0 and 192.168.2.0. Host A sends a request to see email from the Mail Server, what are the destination and source of MAC address and IP address received by the Mail Server?

Now when facing this question we first need to know what will the Host A send to reach the Mail Server.
A Host in a network will only know about its own network, it doesn't know anything about the other network accept for the IP address. So Host A will send the following:

Source MAC : 00-14-BA-AA-AA-AA (the host MAC address)
Destination MAC : 00-14-BA-BB-BB-BB (the router's FA0/0 port MAC address)
Source IP : 192.168.1.2
Destination IP : 192.168.2.2

In term of MAC addresses, remember the host only knows the MAC address of its default gateway (router).
The host will send it to the switch, switch will examine the frame and send it to the port which the router attach to.
Switches always remember the MAC addresses attach to their ports, switches keep this information in its database.

The switch then send it to the router. Router receiving this packet will then examin the packet further. It will check the packet for corruption then strip off the MAC address.
Router will determine where it should forward the packet to, it will first add its own MAC address as the source address and the next hop (router or PC) MAC address as the destination address.
The source and destination IP address will not be altered.

So at last the Mail Server will receive the following information:

Source MAC : 00-14-BA-CC-CC-CC(the router's FA0/1 port MAC address)
Destination MAC : 00-14-BA-DD-DD-DD(the Mail Server's MAC address)
Source IP : 192.168.1.2
Destination IP : 192.168.2.2

Read more!

How To Terminate UTP Cable to Toolless Modular Jack

Last post I talked about how to terminate to Modular Jack, it was not hard at all right? There are also modular jacks type that are toolless.
The toolless jacks allow you to terminate UTP cable without the punch down impact tool, though you still have to use cable stripper and scissor, so they're not exactly toolless.

The one that I once tried using before was the one from AMP, lets see if they really cut down the time in terminating the cables.

The tools you need is exactly the same when terminating to regular jacks, but you can exclude the punch down impact tool and add a cutting tools like scissor or cutter.
Here are the steps:

Step One:

Still same with the regular jacks, strip the cable jacket and untwist the cables.

Step Two:

Insert the cables to the holes according to the color codes printed on the jack

 

Now this process takes a little bit more time if this is your first time terminating cables to toolless jacks.

Step Three:

Cut the excess cables using scissor or cutter, it would be easier to use technician scissor.

Make sure you cut them in even length.

Step Four:

Close the cover using your hand, this is quite hard, just close it until you're sure it's firmly closed, and attach the jack to the wall face plate.

 

There you have it, toolless modular jack termination.

In my opinion, I prefer to use the regular jack instead of the toolless ones, I'm more used to terminate to the regular ones and for me, it's harder to arrange the cables in the toolless jacks.

Then again it's up to you to choose, in term of price, the regular and the toolless jacks are not too much different, but the punch down impact tools do cost some good amount of money.

Read more!

First Steps in Home Network Troubleshooting

When you realized there's something wrong with your home network, you need to do first steps of troubleshooting using this tool I show on the left picture.

Isn't that windows command prompt? you bet it is, you don't need some kick ass software just to find out your home network problems.
I usually jump right to command prompt to find out what happen on my network.

Step One:
You need to type in this command at the command prompt:

ping 127.0.0.1

What this does is pinging your own network card, if you get reply then there's nothing wrong with it, if no reply this means there's a problem with your TCP/IP stack.
There is a question related to TCP/IP stack in the CCNA exam.
You can use the following commands to reset your TCP/IP stack:

netsh int ip reset resetlog.txt


netsh winsock reset catalog

Step Two:
No problem with your TCP/IP stack but still no connection, try pinging other devices in the network.
Say you know your router has IP address of 192.168.1.1 then type the following:

ping 192.168.1.1

If there's replies then you know there's no problem within your internal network, if not type the following to find out whether you got IP from the router if you use DHCP:

ipconfig /all

If you don't get IP from the router do the following to renew your IP

ipconfig /release




ipconfig /renew

Step Three:
Hmmm... you can connect to other devices in your network but can't get to the internet. Try to ping google using:

ping google.com

If you find no replies, try to ping using IP address of external site, for example I know that google.com has 72.14.207.99 IP address then I ping it:

ping 72.14.207.99

If it works out then there's a problem with your ISP's DNS servers, try to contact your ISP about this.
If you still can't get to the internet, try turn off all the devices in your network for about 10 minutes and turn them on again using the following order:

Modem - Router - Switch - Your computer

You need also check your firewall settings, the easy way but not recommended is to shut down your firewall just for a moment and try connecting to the internet while the firewall down. This is to find out if your firewall is blocking your access to the internet.

Now the above steps are only the first steps you need to take if you have problem with your network, there are way too much problems that can happen in a network but you can use these steps for your guidelines in troubleshooting network.

Read more!

OSI Layers in CCNA Exam

Is it really necessary to learn about the OSI layers? yes I'm afraid it is. I know it's a boring theory type, but they really useful for troubleshooting network and there can be a lot of questions in the CCNA exam related to OSI Layers.

OSI layers is a conceptual thing that urge all vendors for network devices to follow their concept so all devices from different vendors can communicate. Long time ago before this concept exist, the devices from one vendor can't communicate with other vendors'.

Basically they say that some functions should exist only on a certain layer and a change in one layer would not affect other layers' functions.
This is how you use OSI layers as troubleshooting tool. You first find out which function of the layer having error, then you can concentrate on that layer's devices to do troubleshooting.
I know it sounds simple, but it does cut your time a lot in troubleshooting.

The OSI Layers are counted from bottom up, starting from layer 1 which is the Physical Layer to layer 7 which is the Application Layer.
The whole seven layers are then divided into two different groups.
Layer 7 to 5 which are the top layers focus on the users of the networks, while the bottom layers 4 to 1 are for the network it self.

In my opinion, the bottom 4 layers are the ones that you as a network engineer or as CCNA candidates should focus more. In case of CCNA, there are many questions related to these bottom 4 layers and some quite easy questions for the upper layers.

Here are the brief descriptions of the functions that each layers do:


Application Layer
It provides the User Interface for the users, in this layer you can find stuffs like database, HTTP, Telnet, FTP, TFTP, etc.
Some questions regarding this layer should be some kind like matching question, to match which items go to which layer, or HTTP belongs to which layer, etc.

Presentation Layer
This layer deals with the presentation of data, encryption, etc.
For CCNA exam, I have never found question related to this layer and also the session layer, but just to be safe, you need to at least understand the function of each layer.

Session Layer
Session Layer handles the data so data on one application won't go to other applications.

Transport Layer
Now from here to bottom layer, are the layers you need to focus on, you need to remember which bottom layers handle which type of transmission unit.
For Transport Layer, it divides data from the upper layers into segments.
Transport layer performs acknowledgement of transmissions to ensure reliable end-to-end transmission (used for WAN connection), sequencing, flow control functions, and error correction before transmission.
The protocols deal with this layer are protocols like TCP and UDP.
In CCNA exam you'd likely get questions like which layer handles WAN, the functions that Transport Layer do, the data structure of TCP or UDP, etc.

Network Layer
This layer handles packet to do logical path selection/logical addressing for your network, this is where you can find IP address as in logical address.
If you know there's a problem related to IP address, you know you should focus on this layer's devices.
The protocols exist in this layer are IP, IPX, etc.
Remember the devices related to this layer such as routers and layer 3 switches.
Related to CCNA, you can find questions like which layer deals with packets or logical address, if you can't ping your network at which layer this problem associated with, etc.

Data Link Layer
Data Link Layer deals with frames as the transmission unit. This layer also handles the physical addressing of your network i.e. MAC Address.
It performs error detection but not error correction, remember this, you can sometime switch this with the function of Transport Layer.
The devices related to this layer are switches and bridges.
You might just find questions for frame, the functions of this layer, MAC address in CCNA exam.

Physical Layer
This layer handles the transmission of bits in network, meaning this is the closest you can get to the physical wiring in your network.
The devices related to this layer? Your NIC, cables, repeaters and hubs. Yes, hubs basically only retransmit bits so they belong in physical layer.

Another thing to note about CCNA question for OSI Layer is that you have to remember how the layers handle data.
From the top to bottom it would be like this.
Data - Segment - Packet - Frame - Bit

There you have it, OSI Layers, some people would just pass on this topic (because it's so boring) and find out later the exam has many questions related to it.
But if you know a little bit about OSI layers, you surely can troubleshoot your network faster.
Just remember not to underestimate any topic for the exam.

Read more!

Network Segmentation

You started your network with small amount of computers and networking devices, sooner or later you want to add this and that, next thing you know your network got slower.

If you have this condition in your network, you might want to consider reviewing back you what devices you have in your network. You might need to segment your network.

You can use switches and bridges to segment your network, if you use them you separate your network collision domain. Remember what collision domain is when I posted about switches.

Like the above picture, if you use switch to connect 4 computers, then you'd have 4 collision domains. On the other hand, if you use hub, then you'd have 1 big collision domain, this will not only slow your network but also pose security problems.

The above picture looks good, but they're still count as one broadcast domain. To break up broadcast domain you can use routers.


What broadcast means is that computers need to send packet all over the network. One example is when you use DHCP to give IP address to all computers, first the computers will send out DHCP Discover message everywhere saying, help I don't know my IP, can anyone give me one?
The fact that computers send a lot of broadcast when connected to a network, the more computers/broadcasts you have, the slower your network will be.

 

When using router to break broadcast domain like this, this means you'd have 2 broadcast domains, in other words, you have 2 network segments within your network.

In CCNA exam, they usually give questions like this, if you have a network with the diagram like the above picture, how many broadcast domains and collision domains exist?

You know you have 2 broadcast domains, but how many collision domains? 

Remember each port in a switch forms one collision domain and routers also the same.

From the above we can tell that the diagram has 6 collision domains.

Read more!

How To Crimp UTP cable to RJ45 Connector

I posted about the tools and the color codes for crimping UTP cable to RJ45 before, now I'd like to share step by step of how to crimp the cable to the connector.

You can see on the left picture how the end result will look like.

I want to review again on the tools that I usually use to crimp my cables. Here are the tools:

They are the same from my previous post about the tools, I use additional tools such as the cable stripper for stripping the cable jacket, and boots just to cover the RJ45 connector making the crimped cables look more attractive and more professional.

Here are the steps to start crimping the cables:

STEP 1

Slide in the boots to your UTP cable, if you don't want to use the boots, you can skip this step.

STEP 2

Strip the cable jacket using the cable stripper, then untwist the cables and arrange them according to the color code.

STEP 3

After you arrange the cables, make the cables look like the below picture and cut them to match the size of the RJ45 connector.
You have to cut the cables so they are aligned.

Most mistakes that people do is to cut the cables too short or too long, it takes time to practice. I found this connector from http://cableorganizer.com/ez-rj45-network-plugs/ to ease people crimping cables.

With this connector you don't need to worry cutting the cables too short/long, you can just slide in the cables through the connector and cut them afterward.






STEP 4

Slide in your cables to the connector, be careful not to change the cables arrangement.

A word of note, sometimes people neglect the importance of connectors positioning. You have to slide in the connectors all the way in. If you look at the connectors carefully, you can see as the picture on the left.

That part is used to hold your cable, when you crimp the connector, that part will squeeze a little bit to the cable and hold it firm.
This is useful so your connector won't easily come off when pulled.


STEP 5

Insert your connector to the crimper thoroughly and then crimp it until you here some noise.

After that check if all the copper parts of the connector are properly in. You can see the difference below between the un-crimped connector and the crimped connector:

 

Why I mention this is that sometimes when you crimp using not so good crimper, you'd get some of the copper still sticking out from the connector.

There you have it, slide the boot to the RJ45 and crimp the other side of the cable so you have your own network cable.

I hope this is useful, happy trying.

Read more!

My Home Network

I know, before you say anything, my home network has very "common" network devices and they're all messed up.
I'm all talking about this and that about networking and this is what I have in my home? yes,  I don't have a lot to spend on my network, time and money, but I'm telling you it's a great pleasure to connect all these things together and see them working.

The device that I'm most proud of is that Cisco Access Point 1242AG. This baby rocks, if only I have more than one of this thing, I can have a roaming connection all over my house. And not like any average AP, I can adjust the strength of the signal and many other parameters.

This is how the diagram for my home network looks like:

I'm using internet cable for my connection, you can see the cable modem there connected to the router. From the router I connect my Access Point and the switch to connect other devices.
The switch used to connect 3 workstations on the first floor for my office, and 2 other workstations for the family.
The Access Point connects my laptop and my lovely Sony PSP. Oh I love my PSP, with the AP I can connect to the internet and get my news feeds and update of the newest games.

After saving for some time I finally get to upgrade my network devices, I'm looking for some Cisco devices to help me on my CCNP exam studying later.
No, they're not expensive, if you buy the used ones, you can get pretty cheap price in ebay.com or other places. I've set my eyes on some of the devices, I already ordered some items and now waiting for the shipments to arrive, yayy.

I think I need the Cisco devices so I can do anything I like with them, do some crazy configurations and all. I've been working using Cisco for quite some time but I can't do anything I like in a production network (the term that is used to call a network that's already established and is serving an organization).

And I certainly hope that I can share my knowledge to help people get their CCNA title, cheers.

Read more!

Color Codes for Terminating UTP Cat5e 4 Pairs

The picture you see on the left is UTP Cat5e 4 pairs cable. You can see the basic colors Orange, Blue, Green, and Brown. Each are twisted with white cable strips with the matching color (e.g. white/orange, white/blue, and so on). Sometimes there are cables with no strips, only white color.

There are wiring standards that you must follow, the T568A and T568B. If you're installing cables on a new network you should always follow these standards, you can use a standard of your own in the older projects as long as other cables are using that standard also.

Here are the T568B andd T568B wiring scheme:

There is a reason why I show this T568B wiring scheme first, I have my own way to remember which cable should go where.
First I remember the pairs of cables, first cable should be:
   1. White/Orange and Orange
   2. White/Blue and Blue
   3. White/Green and Green
   4. White/Brown and Brown
After that I like to remember using numbers, I change the 3rd cable with the 5th cable. There you have it, T568B wiring scheme.
You can remember the cables the way you like.

The next one is T568A wiring scheme. After I arrange the cables as the T568B standard, again I like to use numbers to remember the scheme:

I switch the 1st cable with the 3rd cable.
And then switch the 2nd cable with the 6th cable.

This is only the way I like to remember the wiring scheme, you can use whatever method you prefer.

Next I want to tell you about the Straight-Through cable and the Crossover cable.

If you want to connect two different networking devices such as router-switch or switch-computer you should use the Straight-Through Cable.
One exception is that you should use the Crossover cable to connect router-computer. Why? because router and computer belong to the same level on OSI Layer, I'll talk about OSI layer some other time.

Now Straight-Through cable is a cable with the same scheme on both ends. For example, you use the T568B on one end and the same with the other end, then you'll have a straight-through cable.
Some people debate that you should use T568A for straight-through cable and some people say to use T568B.
If you ask me, it doesn't matter which scheme you used as long you keep it constant in your project.

Next the Crossover cable is a cable with different wiring scheme on both ends, one end use T568A and the other end use T568B.

The more modern networking devices have the ability called Auto MDI/MDIX, this means they can detect what wiring scheme you use, and you can use whatever wiring scheme to connect two different devices.
But just to be save, just follow the standard wiring schemes.

Read more!

Common Home Networking Topology

The following picture shows the common network topology of home networking:

There you can see some of the devices that I talked about. If you use cable internet then you need a cable modem which mostly be provided by the ISP.

You don't actually need a router if you just one to use 1 computer for internet. But if you want to share the internet connection, you'll need additional router for connecting the computers.

But if you use ADSL, you can use ADSL router, there are plenty cheap ADSL router out there. You don't need the modem.

After modem and router, you'll need switch which provide a lot of ports that you can use to connect your computers. The good news is that routers these days come with built-in switch ports, so you don't need to buy additional switch. Mostly the routers have 4 built-in switch ports.

If you want to connect using wireless, you'll need Access Points. Here you can connect your laptops, hand held devices that support wireless connection, and even your gaming console like PSP or XBOX360.

Another good news is that there are routers that also have a built-in Access Point and built-in switch ports - hah - you only need 1 device for your network.

To set the devices are easy work, some vendors also provide installation cd so you can follow all the instruction in the cd. But I promise you it is very easy to make your network up and running.

Read more!

Routers for Newbies

Router, as that left symbol you see depicted, is the device of choice if you want to share your internet connection to other users in your home/office.

Here's the picture, if you subscribe to the ISP (Internet Service Provider) in your area, the ISP will give you a public IP address. This public address is your identity in the internet. It's like your home address, if you want to send a letter to your friend you will send the letter to the local post office (ISP's router) then the local post office send it to other post office (another router). Last the letter shall be sent to your friend's address.

When your friend received the letter, he/she will know where to send back the reply letter, your address should be written on your letter right?
Same thing goes with the routing world. That's what routers do, they route your packets to a known destination. Therefore the routers need to introduce themselves with their neighbors.

Once a router receive a packet they will send the packet to other router which knows the receiver address or knows the other router that might know the address.
Now don't get confused, the router doesn't know every address in the internet, but they work together with other routers to form the internet.

Now why do you need router to share your internet connection? Well, the ISP will usually give you only 1 public IP address which should only be used by only one device.
What routers do also is NAT (Network Address Translation). NAT will translate your public IP address into private IP address.
Private IP address only significant to your local network, meaning everybody else in the internet don't know the IP addresses in your local network, they only know your public address.

The NAT will divide the public IP address for your private IP address, they do that by assigning "ports" for every packet that the computers in your local network send to get to the internet.
Now this is not physical ports as in your computer ports, but more as logical ports, ports like port 80 for your HTTP connection, etc.
For example, computer A send a request to google.com, then the router will assign a port to the request, and when computer B send other request they will be assign other port.
This is how routers know who send the packet.

You need to remember that routers communicate with other routers using the logical address which is IP address, in contrast with switches that communicate using the physical address which is the MAC address of your NIC (Network Interface Card).

Don't worry you don't need to get in depth about this unless you want to take some network certifications. This is the basic concept that you need to know.
Most low end routers have simple configuration to let you set up your network in no time.

Inside of a router is typically same with PC, router has a CPU, RAM, storage media, etc. That's why router and PC are at the same layer of OSI layer.
I'm working on writing about OSI layer, so I'll talk about it later.
For this reason, that's why you have to use crossover cable to connect PC directly to router. Same thing goes when you want to connect 2 switches together.
But if you use low end routers such as from linksys, D-Link you don't need to do this because they have a built-in switch ports - not router ports. You can use the straight-through cable instead.

For the above reason also, you can transform your PC into a router, cool.

Read more!

Switches for Newbies

If you want to connect more than one computer in your network, you'll need switch. Yea, everyone knows that, but how exactly does switch better than other devices such as hub or bridge?

By the way, the picture on the left is a symbol used for depicting a switch, you will usually use this picture to design your network.

Back again on switches, first you need to know about collision in a network. In a network using hub, every data that your computer send is forwarded to all ports in the hub.
For example if computer A sends a data and at the same time computer B also sends a data, the data will collide and cause the hub to stop all transmissions from every device connected to it. This condition not only make the network slower but also pose a security problem.
If one computer send a data then every other computers can "listen" to that packet.

Switches are not the same as Hubs, they remember every computer that plug into their ports. So they will send packets only to the destination computer.
What the switches remember are the MAC addresses of the computers connected to them.
MAC address is a unique value given by the vendors, each vendor has a unique value and unique serials for their products.
There are rarely any two similar MAC address unless because of manufacture defect.

The switches are able to segment collision, meaning that every collision is limited only to the ports that computers are connected.
How the switches do that? well hubs can't do this because they use 1 pair (2 cables) of UTP cable for transmitting and receiving data.
While switches use 1 pair of cable to transmit data and 1 pair to receive data, so there shouldn't be any collision.

Get this, if you buy a 100mbps per port switches, you by no charge will get 200mbps per port, sweet.
How come? because they use full 100mbps for transmitting and 100mbps for receiving data.

Now what is the different between switches and bridges? basically bridges do the same thing as switches, they segment collision.
But switches have much more ports than bridges, that's why switches are often called multiport bridge.

Read more!

Introducing Networking Newbie

Hi there,



This is my first time to write to a blog. Haven't had enough time to write in the previous time due to all the works I had. But now, I am a business owner (well, currently a small business that is) which should give me enough time to share in this blog.



Well, enough said about myself, next step I will regularly write some experiences, articles or how-to on computer networking and internet.

Why Networking newbie you ask? I know the feeling some of you out there willing to learn new things but OMG, we don't even understand a single word experts are saying. So, I want to make this blog as easy as it can get.

So, thats basically telling that I am a newbie too? well, not exactly, i might be not a super expert but I do know a bit things.

I recently got my CCNA, oooh, what a nice card the guys from Cisco sent me, they even allowed me to use the CCNA logo.

Oh, I'm also in to something called SEO, you all probably have heard something about this before. A great thing I'm telling you.



One last thing I want to tell you, I previously hated networking, marketing and in some cases even blogging, honestly I never had a good mark on any of them. Now look at me blogging about all these darn things, I even make a living from them. What I want to say is that things haunted us in the past might coming back to us again, and one way or another we have to accept those things.



Hope you enjoy reading this blog and if you ever feel down on something, don't give up, if you do, you might not be succeed in anything.


Read more!