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Webcast-Catalyst9k
New Member

VLAN

OK, so i know VLAN works on either layer 2 or layer 3. What is the purpose of putting VLAN on layer 2? just to subdivide a switch to function as multiple switches?

Also, the environment i am in currently has 3 vlans (production, dmz, public wireless). i know there should be managment, backup vlans etc, but thats not part of this project scope. Anyways i am going to be changing all the infrastructur to 2 cat 4507s and 6 3000 series switches. Each vlan has a diff. ip schema, ie. production is 10.0.0.x where DMZ is 192.168.2.x etc. so correct me if im wrong but obv i am going to use them on layer 3.

In such i will have a min of 1 VTP server. On each 3000 series switch they will simply add more ports to a vlan. will i use the INT VLAN command or will i keep those on layer 2?

5 REPLIES
Purple

Re: VLAN

Layer 2 is to put all ports that are in that vlan into it's own broadcast domain . They can talk to each other directly without intervention . If they need to talk outside their own domain then you have to have a layer 3 definition . It is a general correlation between a layer 2 vlan and a layer 3 SVI if it needs to be routed . If you have ports that are in a layer 2 vlan and routing is required then you must create a layer 3 SVI .

New Member

Re: VLAN

OK lets take a hypothetical poor practice situation where a company has everything grouped into 1 VLAN that uses 10.0.0.0 with an 8 bit mask. Can this be vlan'd without subnetting?

Hall of Fame Super Gold

Re: VLAN

Brook

If there is an organization's network which is all in 1 VLAN and uses 10.0.0.0/8 and they decide to change it to use multiple VLANs then they will also need to change it to use multiple subnets. Effectively each VLAN needs to be a unique subnet.

HTH

Rick

New Member

Re: VLAN

aside from security benefits does reducing broadcasts affect performance?

Re: VLAN

Think about a 100 users in a flat vlan, and broadcasts going across the network has to be processed by all 100 PCs. If you segment this into two vlans, broadcasts are cut down by 1/2. Performance wise thats half the amount of broadcasts that each nic has to process.

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