router and vlans

Answered Question
Dec 30th, 2007

hi every body

please consider the following scenario.

"r" stands for router

"sw1" for switch1

"sw2" for switch2

router"r" has two fast ethernet interface e1 and e2

router is connected to sw1 by e1 and to sw2 by e2.

both sw1 and sw2 have vlanA configured on their ports.

asumming router has all the proper configurations, Can a user in vlan A on sw1 communicates with a user in vlanA on sw2?

simply put can two similar vlan say vlana

communicate via router with each other?

thanks alot have a nice day

I have this problem too.
0 votes
Correct Answer by Jon Marshall about 9 years 3 weeks ago

Hi

Guru Prasad is correct in that nowadays switches are often L3 capable and so take care of the inter-vlan routing but to answer your question.

Assuming the switches are not connected together and that you are using one IP subnet for vlanA then no because you will not be able to give e1 & e2 an IP address out of the same IP subnet so you could not set this up.

You could bridge between the 2 interfaces on the router which would allow you to do this but then the router is acting at layer 2 rather than layer 3.

Jon

Correct Answer by guruprasadr about 9 years 3 weeks ago

HI,

Pls understand the basic scenario. Normally, the Router will do the L3 routing and can be used for communication between two different VLAN or Routing Protocols.

In your case,

Just Configure an up-link (trunk) between SW1 and SW2 which is higly enough for users in VLANA of both switches to communicate.

Router is not required in this case.

Do RATE if HELPS

Best Regards,

Guru Prasad R

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Correct Answer
guruprasadr Sun, 12/30/2007 - 22:28

HI,

Pls understand the basic scenario. Normally, the Router will do the L3 routing and can be used for communication between two different VLAN or Routing Protocols.

In your case,

Just Configure an up-link (trunk) between SW1 and SW2 which is higly enough for users in VLANA of both switches to communicate.

Router is not required in this case.

Do RATE if HELPS

Best Regards,

Guru Prasad R

Correct Answer
Jon Marshall Mon, 12/31/2007 - 02:54

Hi

Guru Prasad is correct in that nowadays switches are often L3 capable and so take care of the inter-vlan routing but to answer your question.

Assuming the switches are not connected together and that you are using one IP subnet for vlanA then no because you will not be able to give e1 & e2 an IP address out of the same IP subnet so you could not set this up.

You could bridge between the 2 interfaces on the router which would allow you to do this but then the router is acting at layer 2 rather than layer 3.

Jon

zeeshanr202 Wed, 01/02/2008 - 12:59

thanks alot jon.marshall .I really appreciate your help. i got it now

zeeshanr202 Wed, 01/02/2008 - 13:12

i was just thinking about your response. let say there is no one-to-one correspondence between vlanA and ip subnet. rather vlanA on switch1 encompasses major net 192.192.192.0 while vlanA on switch2 encompasses 193.193.193.0

both switches are connected to router via e1 and e2.what would happen in that case? can users in vlanA on sw1 communicate with users in vlanA on sw2?

thanks alot

Jon Marshall Wed, 01/02/2008 - 13:45

Hi

Again, assuming that your switches are not interconnected then yes you would now get connectivity. Because the switches are not connected to each other vlanA on switch1 is not the same vlan as vlanA on switch2.

Jon

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