Switching

Cisco makes some general recommendations to override the default interface settings to make the unused ports more secure. The recommendations for unused interfaces are as follows:

• Administratively disable the interface using the shutdowninterface subcommand.

  
  

• Prevent VLAN trunking and VTP by making the port a nontrunking interface using the switchport mode accessinterface subcommand.

• Assign the port to an unused VLAN using the switchport access vlan numberinterface subcommand

Switching

CDP discovers several useful details from the neighboring Cisco devices:

- Device identifier: Typically the hostname

• Address list: Network and data-link addresses

• Local interface: The interface on the router or switch issuing the show cdp command with which the neighbor was discovered

• Port identifier: Text that identifies the port used by the neighboring device to send CDP messages to the local device

• Capabilities list: Information on what type of device it is (for instance, a router or a switch)

• Platform: The model and OS level running in the device

Switching

To globally disable and enable CDP?

no cdp run

 cdp run

Switching

To enable and disable cdp (Non global, per interface)

no cdp enable

cdp enable

Switching

Commands to set speed and duplex settings on routers and switches?

 speed {10 | 100 | 1000}interface subcommand

  duplex {half | full}interface subcommand

Note that setting both speed and duplex disables the IEEE-standard autonegotiation process

Switching

Which 3 commands list both the speed and duplex settings on an int?

Which one implies how the switch determined the speed and duplex settings?

show interfaces and show interfaces status

show interfaces status

 again, the a - shows autoneg.

Switching

When the IEEE autonegotiation process works on both devices, both devices agree to _ speed supported by both devices?

 the devices use __ duplex if it is supported by both devices, or __ duplex if it is not

Fastest

Uses full duplex  if supported by both devices,

or half duplex if not

Switching

When one device has disabled autonegotiation, and the other device uses autonegotiation, the device using autonegotiation chooses the default duplex setting based on the current speed. The defaults are as follows:

• If the speed is not known, use 10 Mbps, half duplex.

  
  

• If the speed is somehow known to be 10 or 100 Mbps, default to use half duplex.

• If the speed is somehow known to be 1000 Mbps, default to use full duplex.

Switching

Cisco switches can determine speed in a couple of ways even when IEEE standard autonegotiation fails

Switching

By the manual config of speed 100 and duplex full

or the switch senses the speed of the connected device and adjusts

Switching

Will a port show up/up if there is a duplex mismatch?

To identify duplex mismatch problems?

Yup

check the duplex setting on each end of the link, and watch for incrementing collision and late collision counters