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Same Vlan With Different Router Port

http://cozumpark.com/mklresim/InterVLANRouting_1581/clip_image001.jpg

In the figure, there are 2 Vlans that are connected to different router ports.

Withotu changing physical topology, is it possible to add Host C to vlan10?

If not is there a rule that every host that belongs to same vlan must be connected to the same port of the router.

So if I want to add Host c to VLAN10 then, I must disconnect switch B and router and then connect Switch b to Switch a??

Can you please verify those statements?

Thanks...

3 REPLIES
Silver

Same Vlan With Different Router Port

You add switch port to VLAN. But you can't add router port to VLAN. On router you can only set encapsulation, but this usually use for router-on stick.

You are right, yo have to connect swithes directly one to another. And if you want to route between VLANs you can make router-on a stick

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Posted by WebUser Aleksandr Yanovskiy

Silver

Re: Same Vlan With Different Router Port

Hi,

Aleksandr Yanovskiy is correct. That is because a VLAN is basicaly just same as LAN in the aspect of broadcast domain. (V)LAN creates an broadcast domain for all hosts in it. As you know, device capable of separating broadcast domains is router. Because you have router in your scenario it is not possible to have hosts on different ports assigned to the same VLAN (or LAN either). You could also create VLAN 10 on Swicth B and have host C assigned to it - but it would be different an VLAN (with the same name, but vlan 10 on swicth A and vlan 10 on switch B would have nothing in common) and it should also be in different subnet (if you would like to route between networks on both sides of the router).

Best regards,

Jan

Re: Same Vlan With Different Router Port

Could you not use Integrated Routing and Bridging and create a bridge group for each vlan. Using sub interfaces for each physical interface, and then assign a BVI (bridge-group virtual interface). I'm currently trying to do this in a lab network of mine, for redundancy. Both switches will actually be connected to one another in my lab, but that is not needed, you will just need to create the same VLANs manually in both switches.

For more info on IRB check out this doc... not exactly what we're looking at because the hosts are separated by an additional router, but you could imagine two vlans on each switch on the left side:

http://www.cisco.com/en/US/tech/tk389/tk815/technologies_tech_note09186a0080094663.shtml

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