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the cisco's 3-layer model

cisco's 3-layer model comprises of:
access layers.

please explain the funtions of distribution n core or backbone layer. i have a confusion on the working of these two layers. thanx.
Asked by Arnab Chakraborty | Aug 5, 2010 |  Reply now
Replies (1)
Distribution routers aggregate traffic from multiple access routers, either at the same site, or to collect the data streams from multiple sites to a major enterprise location. Distribution routers often are responsible for enforcing quality of service across a WAN, so they may have considerable memory, multiple WAN interfaces, and substantial processing intelligence.

They may also provide connectivity to groups of servers or to external networks. In the latter application, the router's functionality must be carefully considered as part of the overall security architecture. Separate from the router may be a firewall or VPN concentrator, or the router may include these and other security functions.


In enterprises, a core router may provide a "collapsed backbone" interconnecting the distribution tier routers from multiple buildings of a campus, or large enterprise locations. They tend to be optimized for high bandwidth.

When an enterprise is widely distributed with no central location(s), the function of core routing may be subsumed by the WAN service to which the enterprise subscribes, and the distribution routers become the highest tier.
Aug 30, 2010