Routing subnets

Answered Question
May 20th, 2008

Is it true that you can use a router and route between subnets on a lan when all the pc's and the router are connected to only one switch?

I have this problem too.
0 votes
Correct Answer by Amit Singh about 8 years 6 months ago

Well.. you can use the design that you have set up currently but its not a scalable design. The more number of vlans , the more interfaces you need on router. The scalable and the recommended design is to have a trunk between the router and switch and create sub-interfaces for inter-vlan routing between the vlans.

Please see the link below for the same:

http://www.cisco.com/en/US/tech/tk389/tk815/technologies_configuration_example09186a00800949fd.shtml

-amit singh

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Richard Burts Tue, 05/20/2008 - 09:00

Patrick

I am not sure that I really understand your question. So let me answer what I think it is about and if my answer is not what you are looking for then perhaps you can help me better understand what you need.

It is true that if there is a single switch with multiple PCs attached, and if the switch is configured with multiple VLANs, and if the switch connection to the router is a trunk, and if the router supports trunking, then it is certainly true that the router can route between the various VLAN subnets on the switch.

HTH

Rick

Amit Singh Tue, 05/20/2008 - 09:02

If you have multiple subnets and you are using layer2 vlans to segregate those, then yes, you need a router in order to route between them. If you have some other requirement then please explain the network topology.

HTH,

-amit singh

attrib7575 Wed, 05/21/2008 - 07:59

Thanks for the answers everyone! What I meant was routing between subnets on a LAN using a router, but without VLANS. For example: Computer 1 IP: 10.0.0.1 255.255.255.0

Computer 2 IP 172.20.0.0 255.255.0.0

Both attached to same switch. Router with two ethernet ports attached to same switch, computers' gateway addresses are that of the router appropriate router interface with an IP in their same subnet respectively. I would've thought you would need a separate switch for each subnet and couldn't connect both router ports to the same switch. Hope that makes sense :)

Correct Answer
Amit Singh Wed, 05/21/2008 - 08:12

Well.. you can use the design that you have set up currently but its not a scalable design. The more number of vlans , the more interfaces you need on router. The scalable and the recommended design is to have a trunk between the router and switch and create sub-interfaces for inter-vlan routing between the vlans.

Please see the link below for the same:

http://www.cisco.com/en/US/tech/tk389/tk815/technologies_configuration_example09186a00800949fd.shtml

-amit singh

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