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VLANs

Hi:

I have questions about vlans, i have 2 Cisco-3750s connected to Gports and configured as trunk. for example:

Propose configuration:

SW1:

Gports: Trunk mode

fa 0/1: VLAN2

The rest is VLAN1

SW2:

Gports: Trunk mode

fa 0/1: VLAN2

The rest is VLAN1

Do i need to block VLAN1 in the trunk settings of both switches just to make sure the separate vlans won't communicate with each other?

Or by default both vlans won't communicate unless you enable inter-vlan routing?

Im just confuse with the management vlan(VLAN1).

I attach a sample topology for a better view.

thanks

cliff

2 ACCEPTED SOLUTIONS

Accepted Solutions
Silver

Re: VLANs

You can't prune or block VLAN1 since CDP, VTP, DTP are communicate over this VLAN.

How do you use the VTP domains? The two cisco device is in separated VTP domain? If yes I advice to create only one domain with redundant servers or stack the two swithces. Anyway VLAN 1 and 2 have the same same tag in L2 header so they can communicate with other: Vlan2 - VLAN2 and VLAN 1 can with VLAN1...

bye

FCS

Please rate me if I helped.

Re: VLANs

Cliff,

Your understanding is correct. VLANs are separate broadcast domains. You need a layer 3 device, that's configured with IP addresses on SVIs, for a host on one VLAN to communicate with a host on another VLAN.

Hope that helps!

Regards,

Sundar

6 REPLIES
Silver

Re: VLANs

You can't prune or block VLAN1 since CDP, VTP, DTP are communicate over this VLAN.

How do you use the VTP domains? The two cisco device is in separated VTP domain? If yes I advice to create only one domain with redundant servers or stack the two swithces. Anyway VLAN 1 and 2 have the same same tag in L2 header so they can communicate with other: Vlan2 - VLAN2 and VLAN 1 can with VLAN1...

bye

FCS

Please rate me if I helped.

Re: VLANs

Hello,

in addition to Csaba's post, the only way to have Vlan 1 and Vlan 2 communicate with each other is by configuring an SVI on the switches. So, as long as you do not configure:

interface Vlan2

ip address x.x.x.x y.y.y.y

and enable 'ip routing' globally on (one of the) switches, communication between the VLAN's will not be possible.

Regards,

GNT

New Member

Re: VLANs

Hi,

Does it mean that as long as inter-vlan routing and vlan ip address are not configured,vlan1 and vlan2 won't be able to communicate?

Also i haven't configure any ip address for the vlans yet.

thanks

cliff

Re: VLANs

Cliff,

Your understanding is correct. VLANs are separate broadcast domains. You need a layer 3 device, that's configured with IP addresses on SVIs, for a host on one VLAN to communicate with a host on another VLAN.

Hope that helps!

Regards,

Sundar

New Member

Re: VLANs

hi:

Thanks, it helps remove my confusion for VLAN1.

this ticket is closed. thanks again

cliff

New Member

Re: VLANs

Try this put fa0/1 in vlan 1 & for interlan communication you need to do routing.

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