2-tier and 3-tier LAN architectures

[alexanderspa]

i want to know  what's the difference between 2-tier and 3-tier LAN architectures?

[MHM Cisco World]

!

MHM 

[Joseph W. Doherty]

As @MHM Cisco World reply shows, 3 tier has a core, distribution and edge layers/tiers.  A 2 tier combines the core and distribution layers providing core/distribution and edge layers/tiers.  The latter is also know as a "collapsed core".

[Ruben Cocheno · Accepted solution]

@alexanderspa 

 In a 2-tier LAN architecture, there are two main layers: the access layer and the core layer. 3-tier architectures generally offer better scalability due to the distribution layer, allowing for more flexibility in managing and expanding the network. Today, modern architecture on DC use spine and leaf architecture instead of traditional 3-Tier.

[Joseph W. Doherty]

"Today, modern architecture on DC use spine and leaf architecture instead of traditional 3-Tier."

True, but likely only seen in larger/largest DCs.

Conversely, on the smaller DC end, you might only see (logically) 1 tier using a pair of Nexus, using vPC and FEXs.  Such can host a not inconsequential number of hosts.

"3-tier architectures generally offer better scalability due to the distribution layer, allowing for more flexibility in managing and expanding the network."

Also true, but personally I believe a classic 3 tier model owes its preeminence to it handles so much well, i.e. you won't go "wrong" using it.  However, the 3 tier model has so much "clout" often I've seen it difficult to propose other architectures because "it's not 3 tier".  For example reluctance to use a spine/leaf DC architecture, when it would be a better option.