When it comes to configuring interface parameters, there are several that you know know off the top hand. This lab will discuss and demonstrate the most common interface specific configurations that you need to memorize to become a great network engineer.
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.
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)
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)#