Lethe's Ccielogs

Hello all, in the past posts we’ve seen what GNS3 and Dynamips are and how to configure a working lab for our Cisco studies, as I’ve mentioned in the previous posts even if GNS3 is a great and powerful router emulator it can’t emulate, yet, Catalyst switches but I never said it’s impossible to build a switching lab even if with a few differences (mainly in the syntax used).

What you need to start your career in the switching world is :

• GNS3 installed (of course)
• A working IOS of any 3600/3700 router (I’ll be using c3640-is-mz.124-16.bin image)
• This guide

I’ll assume you already have configured GNS3 and imported the proper IOS image. Open up GNS3 and drag a router (or two) into your topology and open up the router properties :

To add switch capabilities to our 3640 router we’ll add an NM-16SW module to slot0, this module will make possible to implement switching capabilities into a single platform if you’re interested you can read more about it here :

Once you’ve done this you can connect the rest of the routers in your topology to the switch’s ports via FastEthernet connections :

As you can see the two routers are connected via FastEthernet connections to our virtual switch, once you’ve done this you’re ready to configure VLANs and trunking betwen your routers/switches. When using an NM16-SW you have to use the "old" syntax to add a VLAN so from the exec mode type vlan database to enter the VLAN configuration mode and be able to add VLANs :

 *Note* If you studying for BCMSN exam keep in mind Cisco deprecated the use of the vlan database to create VLANs, if you’re using a Catalyst switch you should use the global configuration mode vlan <vlan number> syntax. Also note that when you’re using the vlan databse syntax you can’t use CTRL + Z to go back to privileged exec mode but you have to use the EXIT command, if you simply use CTRL+Z IOS won’t commit changes to the configuration and you’ll lose the changes.

Ok this ends this quick "How to configure switching in GNS3", in the next article I’ll show you how to extend the topology and configure the "Router on stick" topology.

Thanks for reading this, Lethe.

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Daniele Catanesi, aka Lethe, is the mind behing Lethe's Ccielogs. He is a veteran of the IT industry with more than ten years of experience in the various fields. Daniele has been mainly working as IT Architect and Trainer for a lot of Enteprise customers implementing cutting edge technologies and complex solutions. Daniele currently holds various certification among which MCITP, CCNP, LPI, Citrix and working tirelessly to his RHCE and RHCA. When he is not busy working or studying for the next exam he writes on the blog trying to give administrators and students around the world tips and suggestion to help them succeed in their career and job.