hi every body!
Campus network, according to my book is designed in hierarchical fashion.
Three layers ,access layer, distribution layer,core layer are the layers, campus network is designed around.
My question is about core layer, implemented using layer 2 switches( i understand it is very rare)
let say distribution switch(multilayer switch) has two links to core switches(layer 2).
Will distribution switch use different subnet for each links connected to core switches (layer 2)? or distribution should use same subnet on each links connected to core.
My impression is the links between distribution switch and core shold be in same subnet which requires distribution switch should same subnet for its links ,connected to core. can we assign same subnet to distribution ports say f0/1,f0/2, connected to core?
thanks a lot!
You definitely would not want to extend a vlan from the access to the core - STP etc. would make this bad pratice. If you want a L2 core you want it to switch packets as efficiently as possible so you absolutely do not want a vlan convergence in the access-layer propogating to the core.
What i was getting at is that in a traditional access-layer, distro, core setup your access-layer vlans are terminated on the distribution switches and are not present in the core.
For the distribution switches to be able to switch traffic across the core there will other vlan(s) not present in the access-layer that are used for this purpose.
The thing to understand is that you will have more than one distro switch connecting to the core. So lets say you have
core1 & core2 connected via a L2 trunk.
distro1 is connected to both core1 and core2
distro2 is connected to both core1 and core2
You can use one vlan to switch traffic across the core from distro1 to distro2 and put all distro ports into that vlan. But note that one of the links from distro1 and one from distro2 will block because of STP.
Alternatively you can use 2 vlans in the core and have one connection from distro1 and one connection from distro2 in one of the vlans and the other connection from distro1 and distro2 in the other vlan.
Each distro switch sees the other distro switch on 2 vlans - sees here being used in the context of a routing peer ie. EIGRP/OSPF neighbor.
Personally i would use 2 vlans across the core.