The Building Block
31
provide redundancy in the distribution layer routing. It can keep core con-
nectivity if the primary routing process fails.
HSRP is covered in Chapter 8.
Dual Core
If you have more than two switch blocks and need redundant connections
between the core and distribution layer, you need to create a dual core. Fig-
ure 1.10 shows a possible dual core configuration. Each connection would
be a separate subnet.
F I G U R E 1 . 1 0
Dual core configuration
In Figure 1.10, you can see that each switch block is redundantly con-
nected to each of the two core blocks. The distribution layer routers already
have links to each subnet in the routing tables, provided by the layer 3 rout-
ing protocols. If a failure on a core switch takes place, convergence time will
not be an issue. HSRP can be used to provide quick cutover between the
Switch block A
Switch block B
Core block
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