Assigning IP addresses on trunk ports in between Multilayer Switches

[mirfanroslan01]

Hi

My network is a star topology and has 3 multilayer switches, model 3650, interconnected to each other with each of them has their own Layer 2 switches connected. At first, I've set up trunking on all of the them, both Layer 2 and Layer 3 switches with VTP done. Trunking done, I assigned IP addresses on Layer 3 switches ports after issuing "no switchport" commands. I got back to one of the Layer 3 switches and started creating VLANs. 

This is where my problem is, the VLAN information wasn't propagating data to layer 2 switches. I got back to ports on Layer 3 that I have assigned with IP earlier, and reconfigure them as trunk port again. Now, the VLAN propagated info to all switches. 

Does anyone have any idea why? And I am worried if I configure Inter-VLAN routing with the ports assigned with IP(not trunk anymore), VLAN interfaces cannot communicate. 

PS: This all is done in Packet Tracer 7.0

Thanks in advance

[Georg Pauwen]

Hello,

as soon as you configure the trunk port as 'no switchport', it will no longer carry layer 2 VLANs. You will need layer 3 VLAN interfaces.

Can you post the Packet Tracer pka file ?

[mirfanroslan01]

Yeah sure. This is just the trial version network of mine. I have another version of layout but without the IP addresses assigned just yet.

[Georg Pauwen]

What is the enable password ?

[mirfanroslan01]

It's jcclass. All of them used the same enable password.

[Georg Pauwen]

Hello,

in order for this to work, you need what is called a router on a stick setup. This involves subinterfaces on the uplink ports, which is not supported on the 3560 switches in Packet Tracer.

Replace one of the switches with a router (the Gateway switch would probably be the most appropriate), and try to configure the router on a stick following instructions from the link below.

HOW TO CONFIGURE ROUTER ON A STICK - 802.1Q TRUNK TO CISCO ROUTER

http://www.firewall.cx/cisco-technical-knowledgebase/cisco-routers/336-cisco-router-8021q-router-stick.html

[mirfanroslan01]

That setup had crossed my mind before.

Well, I tried using this design without the router, proceeded with current and I have a vlan30 host on both J1Smart and J207. But I could not connect them both with them in the same vlan. I don't know what the problem is.

[Georg Pauwen]

Hello,

I have redesigned your network (a bit), all links are now trunk links, and the router is configured for inter-Vlan routing. PC0 and PC1 are clients in Vlan 10 and 50 respectively.

Keep in mind that as soon as you configure a layer 3 link (with IP addresses) between two switches, no VLAN information will be exchanged anymore.

[mirfanroslan01]

Thanks for that, mate. Really appreciate it.

Anyway, if I configure layer 3 links between those multilayer switches, does that mean the inter-VLAN routing won't work anymore?

[Georg Pauwen]

Hello,

if you configure layer 3 links between the multilayer switches, you essentially create separated segments, which means that VLANs will not be propagated to the other switches anymore. You would need to create separate VLAN interfaces on the layer 3 switches, and they cannot be the same on different switches. 

Essentially, not a good idea, since you entire network would break and be separated into multiple segments....

[mirfanroslan01]

Right, I see. Doing so seems like a bad idea. So, right now the best way is to just leave all the trunking ports between layer 3 switches as they are. 

How about routing protocols? Are there any routing protocols that can be implemented on this network? For example, EIGRP or, static or dynamic route??