Safari Books Online is a digital library providing on-demand subscription access to thousands of learning resources.
- Create BookmarkCreate Bookmark
- Create Note or TagCreate Note or Tag
- DownloadDownload
- PrintPrint
Chapter 4. Address Resolution Protocol > Lab Activities
4.16. Lab Activities
4.16.1. Activity 1—Determining Your IP Address and Your Default Gateway
Materials: A Windows computer with a network connection
In Windows, click the Start button.
In the run box, type cmd and press Enter. A command window opens.
Type ipconfig /all. This will display the IP address of your computer. The output will be similar to the following. This shows your IP address and the address of the default gateway.
Windows IP Configuration Mini-PCI Express Adapter Physical Address. . . . . . . . . : 00-22-68-90-D5-DB DHCP Enabled. . . . . . . . . . . : Yes Autoconfiguration Enabled . . . . : Yes IPv4 Address. . . . . . . . . . . : 192.168.15.100(Preferred) Subnet Mask . . . . . . . . . . . : 255.255.255.0 Default Gateway . . . . . . . . . : 192.168.15.1 DHCP Server . . . . . . . . . . . : 192.168.15.1 DNS Servers . . . . . . . . . . . : 24.56.123.4 106.12.34.56 NetBIOS over Tcpip. . . . . . . . : Enabled
4.16.2. Activity 2—Examining the ARP Table
Materials: A Windows computer with a network connection
In the command window, type arp -a. This will provide the same output shown in Figure 4-6. This gives an idea about nodes on the network with whom the computer has recently communicated.
Record the IP addresses you see in this table, as you’ll need them later.
4.16.3. Activity 3—Packet Capture
Materials: A Windows computer with a network connection and packet capture software
To capture the ARP traffic, first clear the ARP table or cache. To do this, type arp -d * in the command window, then type arp -a to verify there are no entries.
In Wireshark, select your adapter and start a capture.
Back in the command window, ping one of the nodes previously listed in the ARP table. In the capture window, you should see the ARP request and ARP reply. These will be followed by the ICMP traffic. In pinging the default gateway, you may see the return ARP. That is, after pinging the gateway and seeing the associated traffic, the gateway generates its own ARP request directed back to you.
4.16.4. Activity 4—Gratuitous ARP
Materials: A Windows computer with a network connection, packet capture software, and a DHCP server like a Linksys router
To see a node ARPing for itself, typically the best time is right after an exchange with the DHCP server. This can be done on startup or by forcing the node to go through the IP address release and renewal process.
Start another capture.
In the command window type ipconfig /release. This forces the node to give up its IP address.
In the command window type ipconfig /renew. This causes the node to ask for an IP address again.
After the DHCP exchange has completed, you should see your node ARP for the very IP address it was assigned during the exchange. This is the gratuitous ARP.
4.16.5. Activity 5—How Long Does an ARP Table Entry Live?
Materials: A Windows computer with a network connection
In the command window, type arp -a to show the other nodes on the network.
Ping one of these nodes to refresh the ARP table entry.
At an interval of about 30 seconds, repeat the command arp -a until the entry disappears from the ARP table. How long did it take?
