Interface Specific Configurations

Real World Application

Statically configuring interface configurations is a common practice in specific areas of the network such as a Data Center or link aggregation. It’s best practice to configure node to node devices statically and node to host dynamically (auto) excluding data centers.. As a network engineer you’ll be required to make such configurations to routers and/or switches in a network quite often.

Lab Prerequisites

Lab Objectives

Lab Instruction

There are several key interface configurations that you’ll be required to know as a Cisco engineer. This lab lists some of the most common interface configuration attributes for a Cisco router.

The first objective of this lab is to statically set the speed of interface FastEthernet0/0 on Router 1 to 100Mbps. This is accomplished by using the speed command within interface configuration mode as shown below;

Router con0 is now available



Press RETURN to get started.



Router>enable
Password: 
Router#configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
Router(config)#interface FastEthernet 0/0
Router(config-if)#speed 100

When statically setting the speed of an interface on a Cisco device, its best practice to statically set the duplex as well, this is accomplished by executing the duplex command within interface configuration mode;

Router(config-if)#duplex ?
  auto  Enable AUTO duplex configuration
  full  Force full duplex operation
  half  Force half-duplex operation

Router(config-if)#duplex full

When dealing with Ethernet WAN links or ipsec tunnel interfaces (outside of the ccna scope) it is common to change the Maximum Transmission Unit (MTU); which is the maximum payload a single packet can encapsulate. To complete Objective 3, you’ll need to execute the MTU # within interface configuration mode.

Router(config-if)#mtu ?
  <1500-1530>  MTU size in bytes

Router(config-if)#mtu 1520

Objective 4. – Configure the bandwidth on interface FastEthernet0/0 to 10Mbps. Do not get this confused with the actual speed of the link as the bandwidth command is used by routing protocols to calculate the dynamic metric. This interface configuration will be discussed further in detail in the upcoming sections.

Router(config-if)#bandwidth ?
  <1-10000000>  Bandwidth in kilobits
  inherit       Specify that bandwidth is inherited
  receive       Specify receive-side bandwidth

Router(config-if)#bandwidth 10000

Objective 5. – Setting the Delay is very much like the bandwidth command; it does not statically set the delay but rather it is used in dynamic routing protocol metric calculation which again will be discussed in later sections. To accomplish objective 5, you’ll need to execute the delay command in interface configuration mode as shown below;

Router(config-if)#delay ?
  <1-16777215>  Throughput delay (tens of microseconds)

Router(config-if)#delay 10000

Note that Delay is measured in microseconds! 1000 microseconds = 1 millisecond

Objective 6 requires us to manually set a MAC address on the FastEthernet0/0 interface. Manually configuring a MAC address is commonly required in a variety of scenarios such as mac address based authentication. To configure the MAC address for FastEthernet0/0, you’ll use the mac h.h.h command as shown below;

Router(config-if)#mac ?
  H.H.H  MAC address

Router(config-if)#mac ca02.0adc.0ef9

To verify this configuration without exiting interface configuration mode, execute the command do show interface FastEthernet0/0 as shown below;

Router(config-if)#do show interface FastEthernet 0/0
FastEthernet0/0 is up, line protocol is up 
  Hardware is i82543 (Livengood), address is ca02.0adc.0ef9 (bia ca02.0adc.0008)
  Internet address is 10.234.51.254/24
  MTU 1500 bytes, BW 100000 Kbit/sec, DLY 100 usec, 
     reliability 255/255, txload 1/255, rxload 1/255
  Encapsulation ARPA, loopback not set
  Keepalive set (10 sec)
  Full-duplex, 100Mb/s, 100BaseTX/FX
  ARP type: ARPA, ARP Timeout 04:00:00
  Last input never, output 00:00:01, output hang never
  Last clearing of "show interface" counters never
  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
  Queueing strategy: fifo
  Output queue: 0/40 (size/max)
  5 minute input rate 0 bits/sec, 0 packets/sec
  5 minute output rate 0 bits/sec, 0 packets/sec
     0 packets input, 0 bytes
     Received 0 broadcasts, 0 runts, 0 giants, 0 throttles
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
     0 watchdog
     0 input packets with dribble condition detected
     663 packets output, 69307 bytes, 0 underruns
     0 output errors, 0 collisions, 2 interface resets
     0 unknown protocol drops
     0 babbles, 0 late collision, 0 deferred
     0 lost carrier, 0 no carrier
     0 output buffer failures, 0 output buffers swapped out
Router(config-if)#

Objective 7 requires us to disable keepalives on interface FastEthernet0/0. First off what is a keepalive? Keepalives are a layer2 frame sent from the device to the device to determine if the Ethernet interface link is up. The device sends the frame out on the transmit ring and if the same frame is not received back then the device knows the the interface is down. To complete objective 7 you’ll need to use the keepalive command. Keepalives by default are sent every 10 seconds and to disable keepalives manually configure keepalives to the value of 0 as shown below;

Router(config-if)#keepalive ?
  <0-32767>  Keepalive period (default 10 seconds)
  
Router(config-if)#keepalive 0

The last objective of this lab is to disable CDP (Cisco Discovery Protocol) on interface FastEthernet0/0. CDP is a layer 2 protocol designed by Cisco to exchange device information with no underlying routed network. When you plug two Cisco devices directly into each other, they will both send and receive CDP frames by default on all ports (excluding frame relay which will be discussed in a later chapter). To disable CDP on a specific interface, execute the no cdp enable command in interface configuration mode as shown below;

Router(config-if)#no cdp enable

To verify all configuration changes you’ve made in this lab you can use the same command you learned in the previous lab do show run interface FastEthernet 0/0 as shown below;

Router(config-if)#do show run interface FastEthernet0/0
Building configuration...

Current configuration : 245 bytes
!
interface FastEthernet0/0
 mac-address ca02.0adc.0ef9
 mtu 1520
 bandwidth 10000
 ip address 172.27.48.254 255.255.255.0 secondary
 ip address 10.234.51.254 255.255.255.0
 delay 10000
 duplex full
 speed 100
 no keepalive
 no cdp enable
end

Router(config-if)#