Identification of Core and Distribution Layer Design

[fahimmemon]

Hi 

I am a CCNA certified and I am doing a job as an IT technician here in UAE. I'm the only IT person in my company. Having no prior experience in networking field, I find myself in a pickle. With the help of CDP, I have figured out the network diagram. I am told that there is a COLLAPSED CORE network running in my company. I cannot identify the Core switches here. My question is how to identify the the core switches? We have two internet connections in two separate buildings. Can somebody please help me out. Please..

[Jon Marshall]

If the core and distribution switches are actually the same physical switches then pick a vlan, find the default gateway for clients in that vlan, telnet to that IP and you should be on one of the switches.  

Jon

[fahimmemon]

Thank you very much. Do you mean to say whichever switch has a default-gateway is considered to be a core switch? I learnt somewhere that the core switch used to be the Root Bridge. Is this sort of a rule that the Root Bridge is actually a core switch(es)?? I'm sorry I'm just learning the concepts. Thanks again.

[Jon Marshall]

Generally speaking with a L2 access layer to L3 distribution switches the default gateways of the vlans are on the distribution switches.

The core switches are used when you need to interconnect multiple distribution switches eg. a campus LAN type environment.

In many sites if you only have one building the core and distribution switches are the same pair of switches but to be precise the default gateways are not on the core but the distribution switches.

If you have a separate pair of core switches you usually connect your distribution switches using L3 links so again the STP root for the vlans would actually be the distribution switches for the vlans they route for and not the core switches.

Separate core switches are basically just a high speed interconnect between your distribution pairs and should be left to do that so the routing between vlans, acls etc. are done locally on the distribution switches and only traffic for remote vlans/IP subnets ie. those on other distribution switches would go via the core switches.

If the same pair of switches is used for both functions then all routing between vlans and routing to remote networks is done by that pair.

Jon