West region network

West region network
TABLE 1 1 . 1
Address Space and Regional Allocation
Region Address Space
North 10.0.0.0/10
East 10.64.0.0/10
West 10.128.0.0/10
South 10.192.0.0/10
West Core
10.128.0.0/10
Northern California
10.128.0.0/14
Central California
10.132.0.0/14
Southern California
10.136.0.0/14
Pacific Northwest
10.140.0.0/14
Utah-Wyoming
10.144.0.0/14
Nevada
10.148.0.0/14
Colorado
10.152.0.0/14
Idaho-Montana
10.156.0.0/14
Arizona
10.160.0.0/14
New Mexico
10.164.0.0/14
366
Chapter 11 
Design Considerations
Each one of these zones contains two distribution routers for redundancy, and each distribution
router has a connection to one of the core routers for its region. California, as you can
see, has three zones because there are so many sites that need connectivity in that state.
Each distribution router also has a connection to two other zones so it can have a fast path
to other portions of the network. Usually these inter-region connections are engineered to
accommodate patterns of heavy traffic between two zones within a region. They also act as
backups in case the connection to the core is disrupted.
Let’s now look at a single zone and see how its address space is further subdivided to meet
the need of the sites within that geographical region. This is where a site is connected to the rest
of the network and where the access routers reside. Figure 11.6 shows the Utah-Wyoming zone
and all its sites.
You can see that access routers connect a single site to the distribution router within the
zone. There can be multiple sites within a single city, but they usually have connections only
back to the distribution routers and not to each other. Address space at this point is allocated
on an as-needed basis. If you are using RFC 1918 addresses, then you can be a little
generous, but if you’re using address space you’ve paid for, then you need to be stingier and
allocate only those addresses needed. You should allocate the number of addresses that you
predict will be needed in about two years. This will allow you enough for growth but will
not allocate too many. Because we are using RFC 1918 address space, each site is allocated
at least one Class C address, with some needing two or four Class C addresses. We are allocating
the 10.144.0.0/24 address space for WAN links.
TABLE 1 1 . 2
The 10 Zones and Their Address Space Allocation
Zone Address Space
Northern California 10.128.0.0/14
Central California 10.132.0.0/14
Southern California 10.136.0.0/14
Pacific Northwest 10.140.0.0/14
Utah-Wyoming 10.144.0.0/14
Nevada 10.148.0.0/14
Colorado 10.152.0.0/14
Idaho-Montana 10.156.0.0/14
Arizona 10.160.0.0/14
New Mexico