The Cisco perimeter router must be configured to have Cisco Discovery Protocol (CDP) disabled on all external interfaces.

CDP is a Cisco proprietary neighbor discovery protocol used to advertise device capabilities, configuration information, and device identity. CDP is media- and protocol-independent as it runs over layer 2; therefore, two network nodes that support different layer 3 protocols can still learn about each other. Allowing CDP messages to reach external network nodes provides an attacker a method to obtain information of the network infrastructure that can be useful to plan an attack.

This requirement is not applicable for the DODIN Backbone.

Step 1: Verify if CDP is enabled globally via the cdp command as shown below.

hostname R3 cdp

By default CDP is disabled globally; hence, the command cdp run will not be shown in the configuration. If CDP is enabled, proceed to step 2.

Step 2: Verify CDP is not enabled on any external interface as shown in the example below.

interface GigabitEthernet0/0/0/1 cdp ipv4 address x.1.34.3 255.255.255.252

If CDP is enabled on any external interface, this is a finding.

This requirement is not applicable for the DODIN Backbone.

Disable CDP on all external interfaces via no cdp command or disable CDP globally via no cdp command.