Enterprise Network Architecture Options – Layer 3 Access Layer (Routed Access)

Routed access is a configuration where Layer 3 is extended all the to access layer switches; one layer further than the distribution layer.

The access layer switches act as Layer 3 gateways for the hosts that they are connected too, as well as providing Layer 2 switching.

Access to distribution Layer 2 trunks are replaced with Layer 3 point to point routed links.

The routed access to distribution can come with some advantages other a traditional Layer 2 model. A first hop redundancy protocol is not required, neither is spanning tree protocol as there are no layer 2 links that need blocked.

Uplink utilisation can be increased with the use of routing protocols, unlike in a FHRP scenario where some protocols leave a standby uplink left unutilised.

Troubleshooting is easier as common tools such as ping or trace route can be used, and convergence is much faster with the use of tools like EIGRP or OSPF.

There is a disadvantage to this model, in that a network will restricted to a single switch, much like the recommendation that a VLAN such not extend beyond a single access layer switch. It may also cost more for a access layer switch with a full Layer 3 feature set in comparison to a Layer 2 model.



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