Lab 4: ARP and Proxy ARP

Lab Objective:

The objective of this lab exercise is for you to learn and understand how ARP and Proxy ARP is used by the router in order to encapsulate the packet before it is sent to a neighbor device.

Lab Purpose:

You must understand how ARP works in order to pass the CCNA exam. You could well be faced with an ARP-related issue to troubleshoot in the exam or in the real world.

Certification Level:

This lab is suitable for CCENT certification exam preparation.

Lab Difficulty:

This lab has a difficulty rating of 4/10.

Readiness Assessment:

When you are ready for your certification exam, you should complete this lab in no more than 10 minutes.

Lab Topology:

Please use the following topology to complete this lab exercise:

Task 1:

Configure the hostnames on routers R1, R2, and R3 as illustrated in the topology.

Task 2:

Configure the IP addresses on the Ethernet interfaces of R1, R2, and R3 as illustrated in the topology (.1 for R1 and .2 for R2, and then .1 and .2 between R2 and R3).

Add static routes so that R1 can ping the host address on R3 and R3 can return the ping. Then check the ARP cache on R1. A default route for all traffic to leave via the Ethernet interface will do.

Task 3:

Use the correct show commands to check:

  1. The ARP cache on R1. What are the times for the learned addresses? Which will not timeout and how can you tell?
  2. What is the entry for R3 and why is it the same as the R2 Ethernet interface?
  3. What does the “–” in the ARP table mean?

Note that your MAC address entries may differ from mine.

Configuration and Verification

Task 1:

Router#config t 
Enter configuration commands, one per line.  End with CTRL/Z. 
Router(config)#hostname R1 
R1(config)# 

Router#config t 
Enter configuration commands, one per line.  End with CTRL/Z. 
Router(config)#hostname R2 
R2(config)# 

Router#config t 
Enter configuration commands, one per line.  End with CTRL/Z. 
Router(config)#hostname R3 
R3(config)#

Task 2:

R1(config)#int f0/0 
R1(config-if)#ip add 10.0.0.1 255.0.0.0 
R1(config-if)#no shut 
R1(config-if)#ip route 0.0.0.0 0.0.0.0 f0/0 

R2(config)#int f0/0 
R2(config-if)#ip add 10.0.0.2 255.0.0.0 
R2(config-if)#no shut 

R2(config)#int f0/1 
R2(config-if)#ip add 192.168.1.1 255.255.255.0 
R2(config-if)#no shut 

R3(config)#int f0/1 
R3(config-if)#ip add 192.168.1.2 255.255.255.0 
R3(config-if)#no shut 
R3(config-if)#ip route 0.0.0.0 0.0.0.0 f0/1

Task 3:

R1#show arp 
Protocol  Address          Age (min)  Hardware Addr   Type   Interface 
Internet  10.0.0.1                -   c213.0a9a.0000  ARPA   F0/0 
R1# 
R1#ping 10.0.0.2 

Type escape sequence to abort. 
Sending 5, 100-byte ICMP Echos to 10.0.0.2, timeout is 2 seconds: 
.!!!! 
Success rate is 80 percent (4/5), round-trip min/avg/max = 16/21/24 ms 
R1# 
R1# 
R1#show arp      
Protocol  Address          Age (min)  Hardware Addr   Type   Interface 
Internet  10.0.0.1                -   c213.0a9a.0000  ARPA   F0/0 
Internet  10.0.0.2                0   c214.0a9a.0000  ARPA   F0/0 
R1#ping   192.168.1.2 

Type escape sequence to abort. 
Sending 5, 100-byte ICMP Echos to 192.168.1.2, timeout is 2 seconds: 
..!!! 
Success rate is 60 percent (3/5), round-trip min/avg/max = 12/30/40 ms 
R1#show arp         
Protocol  Address          Age (min)  Hardware Addr   Type   Interface 
Internet  10.0.0.1                -   c213.0a9a.0000  ARPA   F0/0 
Internet  10.0.0.2                0   c214.0a9a.0000  ARPA   F0/0 
Internet  192.168.1.2             0   c214.0a9a.0000  ARPA   F0/0 

R3#show int f0/1 
FastEthernet0/1 is up, line protocol is up 
 Hardware is Gt96k FE, address is c215.0a9a.0001 (bia c215.0a9a.0001) 
 Internet address is 192.168.1.2/24 

R1#show arp 
Protocol  Address          Age (min)  Hardware Addr   Type   Interface 
Internet  10.0.0.1                -   c213.0a9a.0000  ARPA   F0/0 
Internet  10.0.0.2                1   c214.0a9a.0000  ARPA   F0/0 
Internet  192.168.1.2             0   c214.0a9a.0000  ARPA   F0/0 
R1#

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