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.

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"Corn Roast" at South Union Arts, Chicago, IL, 09.06.08.

Special Thanks to Anna Cerniglia & Caitlin Arnold for facilitating the opportunity and Gudrun Hasle & Bill Friedman for help with photographic documentation.

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How to Build a Network on Twitter

I'm spending so much time on Twitter because I feel it's such an important tool for Network Weavers.

Someone asked me how to get started on Twitter. Some thoughts:

1. Figure out what you want: learning, marketing yourself or something, getting to know new people, just mucking around?

2. If you know other people on Twitter, start following them. Then check out who they follow (we call this getting to know your friends' friends). If their posts look interesting, follow them. Many of them will turn around and start following you. In the first ten days, I started following 38 people and now 31 are following me.

3. Check out twitterlocal.net and see who in your town or neighborhood is on. Follow the ones you know or find interesting.

4. Use search.twitter.com and put in key words to find people interested in the same things you are. I tried civic engagement, transition cities and self-organizing. Then I used TweetBeep.com to keep me posted when anyone says anything about those topics.

5. Think of people you have little connection with: people from different ethnic or racial backgrounds, people with different political views, urban people if your rural (and vice versa), etc.

6. Watch other people's retweets or RTs (they put @person's name) then if you like what that person says, click on their name, read some of their posts and start following them.

7. When someone starts following you, send them a nice note.

8. After awhile, stop following people who never post or who's posts aren't up your alley, and try some new names.

What ideas do you have? For those of you with Twitter experience, what have you found works?

Let us know your experience in getting on Twitter!

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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.

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