The Differences between a 3725 image and an IOU

I am going to help people a lot on this page. Contrary to what people say about the 3725 image, you can SWITCH. The real question is what kind of switching can one do? Well, it really depends on what you are trying to accomplish.

If you are trying to get certified, I’d say you can do approximately 80 percent just using the 3725. The dilemma is if you are learning to use a Cisco switch to PASS a test OR do some kind of config file, your best bet is to either use a Cisco IOU (IOS on Unix) image OR just buy the switch (3750 above version 1).

The IOU is a step up from the 3725 in critical areas. So if you’ve found this page and you want to see the difference without having to download the images and compare them yourself…keep reading.

The first side-by-side shows that you can switch in either image. The 3725 will be on the left and running a default console image in GNS3 on my Windows. But the one on the right is the IOU L2 image in my Linux virtual machine. (see screenshot below).

show vlan vs. show vlan-switch
IOU vs 3725 show vlans

From the image above, the first thing that should pop out at you is that there is a difference in how to display all the vlans that are available by default. In the 3725, because there was a 16 port switch module loaded, you need to enter show vlan-switch. However, MOST people are thinking that you only need to enter show vlans as is the case with the IOU.

This brings us to the most important point to this whole topic. If you are trying to understand the Cisco IOS so that you can build real networks inside GNS3, then the 3725 is your best bet. Otherwise, if one was being totally honest and trying to ace out of a Cisco CCNP switch, the IOU is your best bet. But even the beloved IOU has it’s own limitations as opposed to a full blown Catalyst switch.

So when I was managing the community and reading all the posts and running metrics on the site, my proposal to use an older IOS like the 3725 made sense. It was the most adaptable image and ran well in all OS environments (Windows, Linux and MAC). Why would I support any other? Sure the image falls short for the ‘die hard’ techie, but for starting out? It’s an invaluable place to start.

Also, I’m a ‘hands on’ kind of guy. I’d like to try and take a stab at something. If in the process it seems to make sense to me, I’ll keep going because I am learning something of value. I can’t remember numbers and stats which is the bulk of the technobabble you will hear often from a junior network engineer. With that, I only featured the 3725 IOS and MAYBE the 7200 image because it was useful in practicing port-channel.

After reading more posts of where to find the Cisco IOU in some parent directory or to run the python script that generates a key for it, I realized there is always going to be that set of people that are looking to take shortcuts at a great expense.

And at this point, I will support someone that works hard, but I am not helping anyone that either 1.) wants the config files…you need to know this stuff if you are to seriously work in this field and 2.) if you are inclined to take shortcuts.

As I’ve said, you can easily obtain your CCNA by working either image, but the 3725 is much more stable and forces you to substitute multiple areas of a config file. That is a key skill set to have and making it too easy is not the objective of this entire site. If you want to take shortcuts and obtain the IOU, proceed with caution, but I cannot and will not help in obtaining the IOU or the IOURC.txt file or the python script responsible for cracking the key to creating your own keys.

Getting back to the image, if you see the console with a black background with orange text, that’s coming off my windows box and is most likely a 3725 image. If it’s a black background with white, that’s coming off my Linux virtual machine.

With this legend in hand and mindful of the principals laid out here, it won’t be so cryptic as I have seen in other websites that don’t explain whether they are using the 3725, the IOU or an actual switch. I will help you in figuring that out. The first subheading is reviewing what comes up when I google “CCNP switch sims”.