Lab 10: ARP

View your ARP Table:

1. First you want to connect to Router 1 and view your ARP table.  What command will

do this?

Router>enable

Router#show arp

2. Next you need to assign an IP address of 10.1.1.1 /24  to the Ethernet 0 interface.

Router#conf terminal 

Router(config)#interface Ethernet 0 

Router(config-if)#ip address 10.1.1.1 255.255.255.0 

Router(config-if)# no shutdown 

Router(config-if)#exit 

3. Now view your ARP table again. How many entries do you have now?

Router(config)#exit 

Router#show arp 

4. Select Router2 from the button menu. 

5. Set Router 2's Ethernet 0 interface IP address to 10.1.1.2 /24

Router#conf terminal 

Router(config)#interface Ethernet 0 

Router(config-if)#ip address 10.1.1.2 255.255.255.0 

Router(config-if)# no shutdown 

Router(config-if)#exit 

6. You should now have a connection between your Router 1 and Router 2 Ethernet

interfaces. To ensure that the connection is functional ping your Router 1 Ethernet 0 IP

address.

Router(config-if)#exit 

Router(config)#exit 

Router# ping 10.1.1.1 

7. Now view your ARP table and notice the entry. What address is it and how was it

learned? 

Router#show arp 

8. Now that you have built an ARP table, go ahead and clear it.

Router#clear arp

 

9. View your ARP table one last time and notice what entries are there.

Router#show arp

 

ARP Summary

In this lab you will view the ARP table that is stored in the router. You will also learn

how to clear the router's table as a troubleshooting technique.  The router stores detailed

information obtained from other devices on the network.  The information it collects is

what is referred to as a MAC address and IP address. This information can get corrupted

from time to time which will cause the router to have packet-delivery problems.  When

this happens we must clear the ARP table and have it rebuilt.

You can view the ARP table using the command show arp.  This displays detailed

information about interfaces that are learning MAC addresses.  Looking at the table

below we can see that we learn the IP address and MAC (hardware) address of each

Ethernet interface.  The age is how long we have had the information and the interface is

what interface we learned this information from. 

Notice the age time on the 1.1.1.4 address, this is because it is the IP address of the

Ethernet port that is connected to the router.

Router#show arp

Protocol Address     Age (min)   Hardware           Addr     Type Interface

Internet 1.1.1.2         207           0000.0c32.f57d     ARPA     Ethernet0

Internet 1.1.1.4             -           0060.7062.e040     ARPA     Ethernet0

Router#

You must be in privileged mode to clear the ARP table.  After entering privileged mode

the command to clear the ARP table is clear arp. After you have cleared the ARP table you

can view it again using the show arp command. Notice all the entries have disappeared

with the exception of the directly connected interfaces of the router.

Router#show arp

Protocol Address Age (min) Hardware Addr Type Interface

Internet 1.1.1.2 - 0060.7062.e040 ARPA Ethernet0

Router#