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Network Basics – Cisco Discovery Protocol (CDP)

In Network Basics on April 30, 2011 by carlosfvc Tagged:

Cisco Discovery Protocol (CDP) to carry network information

between spoke (stub) routers and the hub router. ODR provides IP routing information with minimal
overhead compared to a dynamic routing protocol and requires less manual configuration than static routes.

When ODR is configured, the stub routers use CDP to send IP prefix information to the hub router. Stub
routers send prefix information for all their directly connected networks. ODR reports the subnet mask, so it
allows different subnets within the same major network to have different subnet masks. This is known as
variable-length subnet masking (VLSM)
The hub router, in turn, sends a default route to the spokes that points back to itself. It installs the stub
networks reported by ODR in its routing table and can be configured to redistribute these routes into a
dynamic routing protocol. For a next-hop address, the hub router uses the IP address of the spoke router as reported to it by CDP.

CDP uses Subnetwork Access Protocol (SNAP)
CDP updates are sent every 60 seconds by default

Configuring ODR
ODR is configured on the hub router using the router odr global configuration command.On the stub router, there must be no IP routing protocol configured.

cdp timer global configuration command.

verify CDP settings by using the show cdp interface command.

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