30
Chapter 1
The Campus Network
and the core is only a pass-through once the routing has been performed.
Because of this, core links will not carry multiple subnets per link, the distri-
bution layer will.
A Cisco 6500 or 8500 switch is recommended at the core, and even
though only one of those switches might be sufficient to handle the traffic,
Cisco recommends two switches for redundancy and load balancing. You
could consider a 5500 Catalyst switch if you don't need the power of the
6500 or the 8500.
Collapsed Core
A collapsed core is defined as one switch performing both core and distribu-
tion layer functions. The collapsed core is typically found in a small network;
however, the functions of the core and distribution layer are still distinct.
Redundant links between the distribution layer and the access layer
switches and between each access layer switch may support more than one
VLAN. The distribution layer routing is the termination for all ports.
Figure 1.9 shows a collapsed core network design.
F I G U R E 1 . 9
Collapsed core
In a collapsed core network, Spanning Tree Protocol (STP) blocks the
redundant links to prevent loops. Hot Standby Routing Protocol (HSRP) can
Switch block A
Switch block B
Core connectivity
Core
connectivity
Copyright ©2000 SYBEX , Inc., Alameda, CA
www.sybex.com