The Cisco perimeter switch must be configured to have Link Layer Discovery Protocol (LLDP) disabled on all external interfaces.

LLDP is a neighbor discovery protocol used to advertise device capabilities, configuration information, and device identity. LLDP 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 LLDP 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.

Step 1: Verify LLDP is not enabled globally via the command.

lldp run

By default, LLDP is not enabled globally. If LLDP is enabled, proceed to Step 2.

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

interface GigabitEthernet0/1 ip address x.1.12.1 255.255.255.252 no lldp transmit

Note: LLDP is enabled by default on all interfaces once it is enabled globally; hence the command "lldp transmit" will not be visible on the interface configuration.

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

Disable LLDP transmit on all external interfaces as shown in the example below:

SW1(config)#int g0/1 SW1(config-if)#no lldp transmit