Three-layer campus hierarchy

Three-layer campus hierarchy
Because the Access layer provides access to the rest of the network through slower WAN
links, congestion can occur. The Access layer can perform a traffic shaping function to ensure
that congestion is left in check using
Random Early Detection (RED),
Weighted Random
Early Detection (WRED)
, or
Distributed Weighted Random Early Detection (DWRED)
technologies. These technologies randomly drop packets in TCP flows when a buffer starts to
become too full. This will avoid the buffer filling to capacity and the router needing to drop
every packet.
If this is a large remote site, the Access layer router will also need to aggregate routes from
the remote site to reduce the number of routes sent to the Distribution layer. This is usually
not the case since remote sites generally have small networks.