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New Member

vlan

PC A in vlan 2,and PC B in vlan 3,

so can PC A and PC B in same subnet?

7 REPLIES
Bronze

Re: vlan

Vlan means segmentation of the network mean separation of broadcast domain. No they should be in the same subnet.

Cisco Employee

Re: vlan

Each VLAN will be in a different subnet. You can find more on VLANs at

http://www.cisco.com/warp/public/793/lan_switching/3.html

It's a good design to have each VLAN in different subnet, but you can have 2 subnets in the same VLAN by using secondary IP addresses on the rotuer's interface

New Member

Re: vlan

thank you for your answers,

but now let us say if PC A and PC B in different vlans,but they are in same subnets,what will ocuur?

i mean if now i ping from PC A to PC B,is it reachable?

Bronze

Re: vlan

No, the ping will not be reachable no traffic will go to the vlan 1 to vlan b and vice versa unles you have routing or bridging between two vlans

New Member

Re: vlan

Look at it like this:

If you have a 24 port switch and divide the first 12 ports into VLAN A and the second 12 ports into VLAN B and you just keep it this simple then the only way the first twelve ports can talk to the second twelve ports is to have a port on each VLAN plugged into its own separate interface on the router.

The only way a workstation on VLAN A can ping a workstation on VLAN B is to get its packets routed.

Now if you have that same 24 port switch and you have a router that has a fastethernet ports (Cisco2621 maybe) then you can use ISL or 802.1q encapsulation on the switches and router and you can configure subinterfaces on the router for each VLAN and configure a single port on the switch as the trunkport and now you only need one connection to the router. The packet in this case still needs the router to get back to the other VLAN. The trunking command on the switch will allow multiple VLANs to pass traffic over a single connection to the router.

Hope that helps.

New Member

Re: vlan

I think what jfraasch wrote is right.The traffic from one vlan A will not move into vlan B until some layer 3

device is added.So a router should be there to let two vlans talk.

Also the idea of trunking on switch is good.By configuring a switch port into trunk mode we can allow traffic of diiferent

vlan's to go to the router on a single fastethernet interface(with logical interfaces configured for each vlan).

New Member

Re: vlan

How would you do that if you had a 2621 router with Fe0/0 used the incoming/outgoing internet access connected to ISP and Fe 0/1 for the internal network, with a local director and 25 ip's? Would a vlan be good here for a network of 100 computers?

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