3550 VLANs and routing

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Aug 4th, 2006
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OK I am trying to figure something out. A 3550 is a L3 switch. VLANs operate at L2. So if you want to have multiple VLANs that can't talk to each other and you make sure the SVI is not enabled(only see that one in CNA)then you are OK. The minute you issue ip routing all bets are now off. Now the VLANs can route between each other which eliminates the need for the VLANs. Yeah, you could put in a bunch of ACLs but cmon whats the point. Am I missing something here?

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Roberto Salazar Fri, 08/04/2006 - 19:29
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The minute you issue ip routing all bets are now off.

>>> Not exactly, even if you have ip routing enable but if you do not have SVI in which the hosts in the vlan will use for their default gateway, it will still not do inter-vlan communication or routing, unless there is an erternal router.


Now the VLANs can route between each other which eliminates the need for the VLANs.

>>> The vlans are virtual bridge, it bridges all the ports that are in the same vlan. naturally all the host in the same vlan will be able to communicate to one another. HOwever, as you already know they will not be able to talked to another vlan without a help of a L3 device which could be the 3550 itself or an external router.



I hope that cleared some confusion.

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