Redundant Switch Block Design Question

[ksbolton1]

Hello all. Quick question. I'm currently reading up on some CCNP switch topics, started from basics and I encountered the below diagram. ImI just seeking some clarification on why there's a Layer 2 link between the distribution switches. I'm assuming it's because access switch on the right has to be able to send Vlan A traffic over that link in case its link to the distribution switch on the left goes down but I'm unsure. Could someone please help me to understand this?

[Leo Laohoo]

Distro switches are suppose to have high-speed links between the distro and the access switch. Distro switch is also mean to have a large MAC address table.
So access switch 1 needs to send something to a client in access switch 2. But since they 1 & 2 are not connected to each other directly, the data needs to go up to distro, the distro performs his check and finds out where the client in 2 is and sends the data downstream.

[omz · Accepted solution]

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@ksbolton1 wrote: I'm assuming it's because access switch on the right has to be able to send Vlan A traffic over that link in case its link to the distribution switch on the left goes down

Thats right! 

The design is not optimal for a large network because the VLANs are end-to-end (exist on both dist and access switches) and not localised. 

Consider 80:20 Rule for good design practice - 80% of the traffic should not cross the LAN and a good practice is to have local VLANs with Layer 3 routing between them. 

Hope this helps. 

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