This lab exercise explores a Cisco device configured as a DNS server and the ARP cache of a network router.
Lab Topology
Lab Download
All of our lab exercises use EVE-NG as the platform for the emulation server. Download the below exercise file and import into your EVE-NG server as a project file.
Cisco IOL Images:
- Switches :: i86bi_linux_l2-adventerprisek9-high_iron.bin
- Routers :: i86bi-linux-l3-adventerprisek9-15.4.1T.bin
| 02 - The Life of a Packet - Lab Exercise (227 downloads) |
| MD5 Hash: 1b002021acea8b3b0f60e79079eb0c98 |
| SHA1 Hash: ac31073e688cb2957e6f9fc6ea0af557aa5a86c2 |
Lab Exercise
- Configure R1 as a DNS server for the domain ‘training.lab’
- Add the host entries for each router device
Hostname IP R1 10.10.10.1 R2 10.10.10.2 R3 10.10.20.1 - Configure R2 and R3 as DNS clients to the R1 DNS server
- Verify that you can ping each device by using their DNS FQDN (Fully Qualified Domain Name).
- Do you expect to see an ARP cache entry for R1 from the R3 router? — Why or why not?
- Verify the ARP cache on R1, R2, and R3
Lab Exercise – Walk through
- Configure R1 as a DNS server for the domain ‘training.lab’
R1#conf t Enter configuration commands, one per line. End with CNTL/Z. R1(config)#ip domain-lookup R1(config)#ip name-server 10.10.10.1 R1(config)#ip domain-name training.lab R1(config)#ip dns server R1(config)#exit R1#
- Add the host entries for each router device
R1#conf t Enter configuration commands, one per line. End with CNTL/Z. R1(config)#ip host R1 10.10.10.1 R1(config)#ip host R2 10.10.10.2 R1(config)#ip host R3 10.10.20.1 R1(config)#ip host R1.training.lab 10.10.10.1 R1(config)#ip host R2.training.lab 10.10.10.2 R1(config)#ip host R3.training.lab 10.10.20.1 R1(config)#exit R1#
- Configure R2 and R3 as DNS clients to the R1 DNS server
R2#conf t Enter configuration commands, one per line. End with CNTL/Z. R2(config)#ip domain-lookup R2(config)#ip name-server 10.10.10.1 R2(config)#ip domain-list training.lab R2(config)#exit R2# --- R3#conf t Enter configuration commands, one per line. End with CNTL/Z. R3(config)#ip domain-lookup R3(config)#ip name-server 10.10.10.1 R3(config)#ip domain-list training.lab R3(config)#exit R3#
- Verify that you can ping each device by using their DNS FQDN (Fully Qualified Domain Name).
R1#ping r2.training.lab Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 10.10.10.2, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 1/1/1 ms R1#ping r3.training.lab Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 10.10.20.1, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 1/1/3 ms --- R2#ping r1.training.lab Translating "r1.training.lab"...domain server (10.10.10.1) [OK] Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 10.10.10.1, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 1/1/1 ms R2#ping r3.training.lab Translating "r3.training.lab"...domain server (10.10.10.1) [OK] Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 10.10.20.1, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 1/1/1 ms --- R3#ping r1.training.lab Translating "r1.training.lab"...domain server (10.10.10.1) [OK] Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 10.10.10.1, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 1/1/1 ms R3#ping r2.training.lab Translating "r2.training.lab"...domain server (10.10.10.1) [OK] Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 10.10.10.2, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 1/1/1 ms
- Do you expect to see an ARP cache entry for R1 from the R3 router? — Why or why not?
R3#show arp Protocol Address Age (min) Hardware Addr Type Interface Internet 10.10.20.1 - aabb.cc00.5100 ARPA Ethernet0/0 Internet 10.10.20.2 3 aabb.cc00.3110 ARPA Ethernet0/0
ARP requests use broadcast traffic so they are not forwarded by a router. R1 is connected to a different subnet from R3, so R3 will not have ARP cache entries for any device connected to the 10.10.10.0/24 network. It will only contain ARP cache entries for devices within its local network of 10.10.20.0/24.
- Verify the ARP cache on R1, R2, and R3
R1#show arp Protocol Address Age (min) Hardware Addr Type Interface Internet 10.10.10.1 - aabb.cc00.4100 ARPA Ethernet0/0 Internet 10.10.10.2 7 aabb.cc00.3100 ARPA Ethernet0/0 R2#show arp Protocol Address Age (min) Hardware Addr Type Interface Internet 10.10.10.1 7 aabb.cc00.4100 ARPA Ethernet0/0 Internet 10.10.10.2 - aabb.cc00.3100 ARPA Ethernet0/0 Internet 10.10.20.1 6 aabb.cc00.5100 ARPA Ethernet0/1 Internet 10.10.20.2 - aabb.cc00.3110 ARPA Ethernet0/1 R3#show arp Protocol Address Age (min) Hardware Addr Type Interface Internet 10.10.20.1 - aabb.cc00.5100 ARPA Ethernet0/0 Internet 10.10.20.2 6 aabb.cc00.3110 ARPA Ethernet0/0
You will notice that the R2 router has ARP cache entries for both networks. The reason is because he has direct connections to the 10.10.10.0/24 and the 10.10.20.0/24 networks via E0/0 and E0/1.