VLSM Configuration and Verification
Cisco routers do not configure VLSM, enable or disable it, or need any configuration to use it. From a configuration perspective, VLSM is simply a side effect of using the ip address interface subcommand. Routers collectively configure VLSM by virtue of having IP addresses in the same classful network but with different masks.
For example, Example 20-1 shows two of the interfaces from router Yosemite from Figure 20-1. The example shows the IP address assignments on two interfaces, one with a /24 mask and one with a /30 mask, both with IP addresses in Class A network 10.0.0.0.
Example 20-1 Configuring Two Interfaces on Yosemite, Resulting in VLSM
Yosemite# configure terminalYosemite(config)# ...
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