difference between core and Distribution

[knaik99]

in LAN network,

what is difference between core layer switches & Distribution Layer switches in terms of Function?

in LAN network,why it is useful to use 3 layer design rather than 2 Layer design i.e.core + Access

[luis_cordova]

Hi @knaik99,

This link covers the layers and their functions:

https://www.cisco.com/web/learning/netacad/demos/CCNP1v30/ch1/1_1_1/index.html

Regards

[Leo Laohoo]

What answer are you looking for?
The reason why I'm asking is because there are several ways of answering this. One is based on what books says (and what school WANT TO HEAR). Another answer is what is happening "out in the wild".
So we (all) need to know if this question is for educational purposes or real-life technical reason(s).

[knaik99]

Real life technical reason

[Leo Laohoo]

The difference between distro and core are getting murkier and murkier each year.
If you've got a small- to medium-sized network, core and distro can just be a logical representation. Sure, the "core" does all the routing and stuff and the "distro" side of things is when the same physical chassis serves a lot of interconnected and at high speed.
Look at the Catalyst 9500, for example. Is this a core or a distro? If this is a core, what is the distro? If this is a distro, then what is the core?
The 9500 can routing (except NAT). So this is a candidate for a core. The 9500 can easily become a distro by connecting access switches.
NOTE: I'd consider the 9400 more line a distro and access hybrid.

[Zanthra]

The function of core and distribution switches is to some extent based on the physical layout of your network. If you have an office building for example, each floor could have a pair of distribution switches, all connected to the core switches in the main server rooms. This helps simplify wiring and helps prevent bottlenecks.

If for example had a large amount of traffic between floors 4 and 8, and similarly between 6 and 10, a ring layout with each floor connected to the one above and below would require the links between the switches on floors 6, 7, and 8 to handle both the 4-8 and 6-10 traffic. The core and distribution tree avoids sending the data over unnecessary links.

Depending on the size of the network and the ammount of data transferred, you really don’t need all the layers.

Using layer 3 at the access or distribution layer means that inter VLAN traffic does not have to go as far before being routed to the other VLAN. Two computers on different VLANs connected to the same switch that want to connect have to talk to the router for the destination VLAN. If the only layer 3 routing is at the core layer, the traffic has to go all the way up to the core layer and back down to the same switch, utilizing those links. With layer 3 switches before the core layer, the computers can be configured to use their access or distribution switch as their router, and the traffic can be switched to the other VLAN locally without going up to the core layer.

[Joseph W. Doherty]

Logicaly, the core's primarily, to almost only, function is forwarding packets as quickly as possible, while distribution's function also encompasses "policy stuff". The thinking behind this logical breakout is, the core might need to handle much more traffic, per device, so its forwarding capacity isn't to be burdened by additional policy processing. Physically, a core L3 device is likely is more "powerful" than a distribution device, while a distribution device might have additonal features not found on a core device, although the same series of L3 swtichsz might be used in both core and distribution roles or even, in a collapsed core design, one device handles core and distribution.