Study Session Number 4! Three Layer Model, Collapsed Core and Spine-Leaf! #5

Hi Everyone! 

The three layer model can be split into three manageable sections (Duh!) - 
Access - The lowest level, this is providing users with a connection to the network so its very basic.
Distribution - Middle level, policy based connection, connects to the top and bottom levels.
Core (or backbone) - The core layer is essentially used to provide fast data transfer between areas.

I remember this by the acronym ADC (makes me think of LoL, if you know what that is ;) )

To better understand the layers, understanding what functions that each layer can do helps - the access layer does Layer 2 switching, PoE, ARP Inspection, VACL's (Virtual Access Control Lists), an easy way to remember what the access layer does is to just think of an access layer switch and the functions the switch provides. The distribution layer handles ACL's, Routing (for LAN & VLANS), Link Aggregation of LAN's and WAN's. The core layer is what I said it was, fast data transfer! that and reliability with fault tolerance.  

With the Collapsed Core model this is similar to the three tier in that the collapsed core gets rid of the distribution layer and leaves just the Access and Core layers. 

The spine-leaf is laid out in the same was as the collapsed core, each leaf (access device) connects to the spine (core devices) from here the communication between all the access devices and the core devices can be created through multiple links, this also creates redundancy and fault tolerance if any of the links go down.  

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