Question about VLAN Trunking and routers

kadshahkadshah Member Posts: 388 ■■■□□□□□□□
I'm a little confused on VLAN operation. I understand that you
need a trunk for different VLAN's to span multiple switches and
that 2 VLAN's communicate by sending packets to the router
which in turn fowards the packet back to the other VLAN but
lets say you have 2 switches each with the same VLAN that is
to say one with VLAN 10 the other with VLAN 10 do I need a router
for this? Is trunking necessary or do I just setup up a physical
connection and what would the physical connection be a cross
over cable between the 2 switches?

I'm so icon_confused.gif


  • mp3spymp3spy Member Posts: 86 ■■□□□□□□□□
    Not sure if I understood your question or not but in response to my some what vague interpretation,
    You still need a trunk to span across different access nodes (switches) in this case. Regardless if they're in the same VLAN or not. Although, if you have one switch that contains multiple VLANs you still need a trunk connection back to the router to either forward it or filter it back to the switch, provided you have 802.1q as the encap. Now in the case of having lets say four switches in which two switches are part of one VLAN and the other two are part of another VLAN. Its probably your best best to enable VLAN pruning...Don't forget to setup VTP as well...

    Correct me If I'm wrong please...

  • kadshahkadshah Member Posts: 388 ■■■□□□□□□□
    You still need a trunk to span across different access nodes (switches) in this case. Regardless if they're in the same VLAN or not.

    that's all i needed to know.
    and yes i forgot all about prunning.


  • Danman32Danman32 Member Posts: 1,243
    Actually, you don't HAVE to have a trunk to bridge VLANs between switches. You could use a dedicated port per VLAN to bridge the VLANs, but if you had 10 VLANs, you'd need 10 physical connections to bridge each of the VLANs across the switches. Consider each VLAN as if it were a separate switch consolidated into one box. Trunking lets you consolidate the connections for all the VLANs.

    Same is true from switch to router. You could connect the individual VLANs to a router using a separate port, or consolidate the connections to one trunk port, then break out the individual VLANs into separate VLAN subinterfaces at the router.

    Another way to look at it. Consider CAT5. It has 4 pairs in one cable. Each pair can be used separately. Putting electrical AC characteristic requirements aside for a moment, you could just as easily use 4 separate speaker or doorbell hookup wire to do the job of one CAT5. Both ways, you carry 4 separate signals.
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