Your ASCII art didn't work, at least for those of us who read this on the Web. The posting software replaces multiple spaces with one space. Argh.
But, I think I understand your confusion and my advice is to leave L3 switches (i.e. routers) out of the scenario to understand the basic features of VLANs. A VLAN is a broadcast domain. If you really want VLAN 1 to be defined in both Building A and Building B, then you have to be using L2 switches. The switches have to forward broadcasts. The host in the VLAN have to be able to broadcast to each other. L3 switches (routers) don't forward broadcasts. Throw L3 switches (routers) into the mix and you break the simple design. When a host in Building A VLAN1 ARPs to find a host in Building B VLAN1, it won't work. ARP uses broadcasts. (Well, proxy ARP would make it work, but that's beside the point.) You could probably get your example to work with some bizarre configuration on the router, maybe? But it would be missing the point. Are you reading Cisco LAN Switching by Clark and Hamilton? That's the book to read. It has a lot of advice on network design. It also has a lot of bad things to say about the "flat earth" design where VLANs spread out over the internetwork. Priscilla Stephen Hoover wrote: > > Ok, I am really struggling to understand the usefulness of > VLANs here. In > the Switching exam book, it states that VLANs remove the > physical boundaries > of the network and a user anywhere on the network can be a > member of any > VLAN (IP subnet). Now I do understand this concept, but > consider the > following scenario.. > > > Building A > Building B > > > VLAN1-----Switch1 Switch 1 > VLAN3 > > | | > VLAN2----Switch 2 Switch 2 > VLAN 1 > > | | > > | | > L3 switch A------CORE--------L3 switch B > (has router engine) (has router > engine) > > \ / > > \ / > > \ / > > \ / > > \ / > > \ / > Servers > VLAN 4 > > > Now lets say that VLAN1 is defined in building A, but some > people in > building B need to be part of VLAN1. Doesn't that make L3 > Switch A the > default gateway for the VLAN1 user in building B? In which case > that user > has to cross the core back to switch A to get his routing to > the servers? > Why would you EVER want a network configured this way?? Or even > worse, what > if your respective gateway was 3 or 4 L3 switches away? That > just doesn't > seem practical to me. > > > Thanks! > Stephen Hoover > Dallas, Texas > > Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=63179&t=63173 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
