Final Words on #CCNA Lab Router IOS

 In 200-301 V1 CCC No Category on Purpose, CCENT-OLD, LabGear

You buy your used #CCNA router, and whoops – you didn’t check the IOS that was installed. You start to try a few commands, notably, the IPv6 config commands, and unfortunately, they aren’t supported. And then you try to download a new IOS from Cisco, and either see tons of legalese about paying if you download and haven’t paid before. Or, the web download pages may reject you so you can’t even get to the IOS.

Today’s post wraps up this CCNA lab series’ posts about IOS, with some final comments on how to avoid this kind of issue by making sure you have the right IOS version and feature set combination before you buy.

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Earlier posts in this series:

Explanation by Example: You Go for IOS 15.1

As you may recall from some earlier posts, several old router models (read: possibly-cheap used router models) support IOS 15. Cisco advertises CCNA as being “IOS 15.x”, and several older router models support IOS 15.0M and 15.1M. These older models do not support 15.2M, which happened to be the latest 15.x M-version available when CCNA was in development.

To help you choose which router model, and which feature set, has the most CCNA features, I’ve updated a reference web page at my web site (linked below). This example walks through some of the data in that web page, specifically for IOS 15.1M and 15.0M.

Pick the Best Feature Sets

First, look at the lists above each table. For IOS 15.1M, that web page lists seven combinations of IOS feature set plus router models, with the implied major version 15.1M. Scan those tables without thinking about each feature listed in the left columns. Which feature sets appear to be best?

Clearly, Columns 3, 4 and 7 show the most X’s. Each X means that the feature on the left is claimed to be supported by the feature set + IOS version + router model. In this case, numbers 3, 4, and 7 match best, namely:

  • Advanced IP Services (1800, 2800)
  • Advanced Enterprise Services (1800, 2800)
  • Advanced IP Services (871, 877)

Note that I did not search every combination of router model, feature set, etc., but picked some that I thought would be most relevant based on used router pricing. But you can look back at the last several posts and learn enough to do your own research.

Compare IOS 15.0M Vs. 15.1M

Next, compare the tables for 15.1M (two tables, one for ICND1 features and one for ICND2 features) to the similar tables for IOS 15.0M. I used the exact same feature set and router model combinations. If you look closely, you’ll see:

  • Those same three IOS feature sets have the broadest support for CCNA features (both ICND1 and ICND2)
  • The feature sets labeled 6 and 7, both for the 870 series routers, don’t have GLBP nor EIGRPv6 support (per Cisco feature navigator).

Advice and Thoughts on Getting 15.1M or 15.0M

Allow me to summarize a bit of advice while wrapping up the discussion of 15.x.

First, before you buy, check the feature set in addition to the IOS version.

Second, it may be hard to find used routers with 15.1M, and easier to find them with 15.0M. As you can see from the web page (based on the Cisco feature navigator), with those three feature sets in particular, the differences between 15.0M and 15.1M are small, at least for CCNA features. So, going with a cheaper router that has 15.0M may be plenty good enough – as long as it has the right feature set. But it’s worth getting 15.1M if available.

Make sure to check that the used router has enough RAM and flash to support the IOS version/feature set. That may sound strange, thinking that if the IOS is already installed, there must be enough RAM and flash. However, the following could happen: You buy the old device, which actually has its old IOS version, and you also get a DVD with a newer IOS. You try to install the new IOS, and then have to do memory upgrades – and spend more $. (To check, go to, walk through the steps to download that specific IOS version and feature set, and the site will display the minimum RAM and flash required.)

Still nervous? And planning to buy more than one router? Buy only one, unpack it, and start typing a sampling of the config commands in the summary tables in the backs of the chapters of my book. For instance, try some IPv6 commands, even if you haven’t read that far. If the feature isn’t supported, the config command will be rejected. If the commands are accepted, the related feature is there, and you can go buy the other routers with the same specifications.

Scan IOS 12.4T, to See That it Still Works for the New CCNA

To end today’s post, we’ll take a quick look at IOS version 12.4T features. Go back to the web site again, and scroll down to the section for 12.4T. Of note:

  • I used eight different combinations of IOS feature set and model (with IOS 12.4T implied in this section).
  • The first six combinations are either for 1721’s, 2600XMs, or both.
  • The final two combinations are for the 871 and 877.
  • Several options support most every CCNA feature listed in the two tables in this section.
  • Note that in some cases, I was a little more distrustful then average about the data I saw in the Cisco Feature Navigator.

After scanning the data, you should see a couple of three nice options – one for 1721’s, one for 2600XMs, and one for the 871/877. And I’m sure the 1721s and 2600XMs will be cheaper – prices coming in the next post or two!



Certskills Web Page w/ #CCNA Features, Versions, Updated
Used #CCNA Router Pricing Process
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Hello Wendell,

I hope you can help me here. I have bought an 1841 router with 15.1M IOS. Following is the part output from “show version” command shows.

“Cisco IOS Software, 1841 Software (C1841-ADVENTERPRISEK9-M), Version 15.1(4)M6”
“System image file is “flash:c1841-adventerprisek9-mz.151-4.M6.bin”

From the page “CCNA Router IOS Features” it seems that this particular combination should have all the features that I need for CCNA. But when I look at Cisco Feature navigator I don’t find “IEEE 802.1Q VLAN Trunking” listed. I get the following list of features

Bridging between IEEE 802.1Q vLANs
IEEE 802.1Q ISL VLAN Mapping
IEEE 802.1Q Tunneling
IEEE 802.1Q VLAN Support
IPv6 Data Link: VLANs using IEEE 802.1Q Encapsulation

Its seem quite odd as nearly every router model supports trunking accept this one which supports everything else and whatever I know about networking (which is very little) its seems a very basic functionality for a router to support.


Hi Jamal,
Feature Navigator can be spotty at times on individual line items. For instance, with that one item not listed, but several others that appear to rely on 802.1Q support, there are good reasons to believe the support is there. However, because you already own the routers, just do this quick test:
1) power on a router and get into config mode
2) issue “interface f0/0.1”
3) type “encapsulation dot1q 1”

If the IOS accepts the last command, you’ve got support for .1Q and ROAS for CCNA practice.


Thanks for that. I was getting bit worried. I missed out a small detail though in my first post. I have bought the router but I haven’t got it yet hopefully in the post but thanks to this BLOG before I bought it asked for the “show version” output and used Cisco Navigator to confirm it has got all the features that I will possibly need.


I got my router today and ran the command you recommended and they ran OK. Thanks for the help.

[…] Final Words on CCNA Router Lab […]


I just purchased cheapest LAB on the Ebay with all routers 15.1 IOS , as you mentioned above I did research and it looks like c2800nm-advsecurityk9-mz.151-4.M7.bin installed, perfect for NEW ICND1/ICND2
I thought it will be helpful to let others know as well.
Ebay Item: 141220216083


Is there a lab manual or workbook for your 100-105 book?


Hi Anorthway,
There’s no lab manual that matches my 100-105 book. That said… there’s a simulator that organizes the labs with references to the book chapters and parts. And the Cisco Networking Academy las lab books on the same content. Let me know if those are interesting to you and I’ll post more details (if you can’t find them).

Would love your thoughts, please comment.x