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Re: Collapsed Backbone [7:41418] posted 04/14/2002
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Georg Pauwen wrote:

> 4A collapsed backbone has high-bandwidth uplinks from all segments and
> subnetworks to a single device, such as a Gigabit switch, which serves as a
> single point for monitoring and controlling the network4.
>
> The following link contains a figure detailing the collapsed backbone
design
> using a Cat4908G-L3:
>
>
http://www.cisco.com/univercd/cc/td/doc/product/lan/c2900xl/29_35wc/sc/swgover.htm

Another way to look at collapsed backbones is to consider why it's called
"collapsed".
Cisco uses a hierarchical campus model that scales down to small one-room
networks and
up to enterprise-wide networks that include multiple buildings. The full
model has
three "tiers" or "layers" (access, distribution, core) and multiple types of
building
blocks (switch block, core block, server block, mainframe block, WAN block).
I don't
have statistics but I've seen a lot more collapsed networks than networks
that fit the
full 3-tiered multi-block multi-building campus model.

The collapsed model is very popular and can scale up to hundreds of
endsystems and
dozens of workgroups (VLANs). All you need is a high-end switch, gigabit
cabling
(preferably fiber but cat 5e/6 works just fine if you keep the cable lengths
in the 90m
range and if you don't have EMI to worry about), and a high-end router to
serve as a
firewall and gateway to the outside. Some of the endsystems can be home-run
directly
back to the main switch, or they can be aggregated at active or passive
consolidation
points. The router can be a standalone or can be included in the same
chassis as the
main switch such as a "route service module" or "layer 3 services module".

Cheers,
-- TT




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