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How would you communicate with a device when you don’t have the IP?

You might be in a situation where you don’t have the IP address of a device in a local network, but all you have is records of the MAC or hardware address.

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Or your computer is unable to display its IP due to various reasons, and you are getting a “No Valid IP Address” error.

Finding the IP from a known MAC address should be the task of a ReverseARP application, the counterpart of ARP.

But RARP is an obsolete protocol with many disadvantages, so it was quickly replaced by other protocols like BOOTP and DHCP, which deal directly with IP addresses.

In this article, we’ll show you how to find IPs and device vendors using MAC addresses with different methods for free.

Understanding ARP

Ip Tracer For Mac Windows 10

ARP (Address Resolution Protocol) is the protocol in charge of finding MAC addresses with IPs in local network segments.

It operates with frames on the data link layer.

As you might already know, devices in the data link layer depend on MAC addresses for their communication.

Their frames encapsulate packets that contain IP address information.

A device must know the destination MAC address to communicate locally through media types like Ethernet or Wifi, in layer 2 of the OSI model.

Understanding how ARP works can help you find IPs and MAC addresses quickly.

The following message flow diagram can help you understand the concept:

1. The local computer sends a ping (ICMP echo request) to a destination IP address (remote computer) within the same segment. Unfortunately, the local computer does not know the MAC address… it only knows the IP address.
2. The destination hardware address is unknown, so the ICMP echo request is put on hold. The local computer only knows its source/destination IP and its source MAC addresses. ARP uses two types of messages, ARP Request and Reply.

The local computer sends an ARP REQUEST message to find the owner of the IP address in question.

This message is sent to all devices within the same segment or LAN through a broadcast MAC (FF:FF:FF:FF:FF:FF) as the destination.

1. Because the remote computer is part of the same network segment, it receives the broadcast message sent by the local computer. All other computers in the LAN also receive the broadcast but they know that the destination IP is not theirs, so they discard the packet. Only the remote computer with destination IP, responds to the ARP REQUEST with an ARP REPLY, which contains the target MAC address.
2. The local computer receives the ARP REPLY with the MAC address. It then resumes the ICMP echo request, and finally, the remote computer responds with an ICMP echo reply.

Finding IPs with ARP

You can use ARP to obtain an IP from a known MAC address.

But first, it is important to update your local ARP table in order to get information from all devices in the network.

Send a ping (ICMP echo reply) to the entire LAN, to get all the MAC entries on the table.

To ping the entire LAN, you can send a broadcast to your network.

Open the Command Prompt in Windows or terminal in macOS and type.

ping 192.168.0.255

My subnet is 192.168.0.0/24 (mask of 255.255.255.0), so the broadcast address is 192.168.0.255 which can be calculated or found with a “Print Route” command in Windows or a “netstat -nr” in macOS. Or can also be obtained with a subnet calculator.

For Windows:

Step 1.

• Open the CMD (Command Prompt)
• Go to the “Start” menu and select “Run” or press (Windows key + R) to open the Run application
• In the “Open” textbox type “cmd” and press “Ok”.

This will open the command-line interface in Windows.

Step 2.

• Enter the “arp” command.
• The arp command without any additional arguments will give you a list of options that you can use.

Step 3.

• Use the arp with additional arguments to find the IP within the same network segment.
• With the command “arp -a” you can see the ARP table and its entries recently populated by your computer with the broadcast ping.

Step 4.

• Reading the output.
• The information displayed in the arp-a is basically the ARP table on your computer.
• It shows a list with IP addresses, their corresponding physical address (or MAC), and the type of allocation (dynamic or static).

Let’s say you have the MAC address 60-30-d4-76-b8-c8 (which is a macOS device) and you want to know the IP.

From the results shown above, you can map the MAC address to the IP address in the same line.

The IP Address is 192.168.0.102 (which is in the same network segment) belongs to 60-30-d4-76-b8-c8.

You can forget about those 224.0.0.x and 239.0.0.x addresses, as they are multicast IPs.

For macOS:

Step 1:

• Open the Terminal App. go to Applications > Utilities > Terminal or Launchpad > Other > Terminal.

Step 2:

• Enter the “arp” command with an “-a” flag.
• Once you enter the command “arp -a” you’ll receive a list with all ARP entries to the ARP Table in your computer.
• The output will show a line with the IP address followed by the MAC address, the interface, and the allocation type (dynamic/static).

Finding IPs with the DHCP Server

The Dynamic Host Configuration Protocol (DHCP) is the network protocol used by TCP/IP to dynamically allocate IP addresses and other characteristics to devices in a network.

The DHCP works with a client/server mode.

The DHCP server is the device in charge of assigning IP addresses in a network, and the client is usually your computer.

For home networks or LANs, the DHCP Server is typically a router or gateway.

If you have access to the DHCP Server, you can view all relationships with IPs, MACs, interfaces, name of the device, and lease time in your LAN.

Step 1.

• Log into the DHCP Server. In this example, the DHCP server is the home gateway.
• If you don’t know the IP address of your DHCP Server/ Gateway, you can run an ipconfig (in Windows) or ifconfig (in macOS/Linux).
• This particular DHCP Server/Gateway has a web interface.

Step 2.

• Enter the IP address on the search bar of the web browser, and input the right credentials.

Step 3.

• Find the DHCP Clients List.
• In this TP-Link router, the DHCP Server functionality comes as an additional feature.
• Go to DHCP > DHCP Clients List. From this list, you can see the mapping between MAC addresses and their assigned IPs.

Using Sniffers

If you couldn’t find the IP in the ARP list or unfortunately don’t have access to the DHCP Server, as a last resort, you can use a sniffer.

Packet sniffers or network analyzers like Nmap (or Zenmap which is the GUI version) are designed for network security.

They can help identify attacks and vulnerabilities in the network.

With Nmap, you can actively scan your entire network and find IPs, ports, protocols, MACs, etc.

If you are trying to find the IP from a known MAC with a sniffer like Nmap, look for the MAC address within the scan results.

How to find the Device and IP with a Sniffer?

Step 1.

• Keep records of your network IP address information.
• In this case, my network IP is 192.168.0.0/24. If you don’t know it, a quick “ipconfig” in Windows cmd or an “ifconfig” in macOS or Linux terminal can show you the local IP and mask.
• If you can’t subnet, go online to a subnet calculator and find your network IP.

Step 2.

• Download and open Nmap.
• Download Nmap from this official link https://nmap.org/download.html and follow its straightforward installation process.

Step 3.

• Open Nmap (or Zenmap) and use the command “sudo nmap -sn (network IP)” to scan the entire network (without port scan).
• The command will list machines that respond to the Ping and will include their MAC address along with the vendor.
• Don’t forget the “sudo” command.
• Without it, you will not see MAC addresses.

Finding out the device vendor from a MAC address

Ok, so now you were able to find out the IP address using “arp -a” command or through the DHCP Server.

But what if you want to know more details about that particular device?

What vendor is it?

Your network segment or LAN might be full of different devices, from computers, firewalls, routers, mobiles, printers, TVs, etc.

And MAC addresses contain key information for knowing more details about each network device.

First, it is essential to understand the format of the MAC address.

Traditional MAC addresses are 48 bits represented in 12-digit hexadecimal numbers (or six octets).

The first half of the six octets represent the Organizational Unique Identifier (OUI) and the other half is the Network Interface Controller (NIC) which is unique for every device in the world.

There is not much we can do about the NIC, other than communicating with it.

But the OUI can give us useful information about the vendor if you didn’t use Nmap, which can also give you the hardware vendor.

A free online OUI lookup tool like Wireshark OUI Lookup can help you with this.

Just enter the MAC address on the OUI search, and the tool will look at the first three octets and correlate with its manufacturing database.

Final Words

Although the RARP (the counterpart of ARP) was specifically designed to find IPs from MAC addresses, it was quickly discontinued because it had many drawbacks.

RARP was quickly replaced by DHCP and BOOTP.

But ARP is still one of the core functions of the IP layer in the TCP/IP protocol stack.

It finds MAC addresses from known IPs, which is most common in today’s communications.

ARP works under the hood to keep a frequently used list of MACs and IPs.

But you can also use it to see the current mappings with the command arp -a.

Aside from ARP, you can also use DHCP to view IP information. DHCP Servers are usually in charge of IP assignments.

If you have access to the DHCP server, go into the DHCP Client list and identify the IP with the MAC address.

Finally, you can use a network sniffer like Nmap, scan your entire network, and find IPs, and MACs.

If you only want to know the vendor, an online OUI lookup like Wireshark can help you find it quickly.

Ip Tracker For Pc

5.3.1.3 Packet Tracer – Identify MAC and IP Addresses

From year to year, Cisco has updated many versions with difference questions. The latest version is version 6.0 in 2018. What is your version? It depends on your instructor creating your class. We recommend you to go thought all version if you are not clear. While you take online test with netacad.com, You may get random questions from all version. Each version have 1 to 10 different questions or more. After you review all questions, You should practice with our online test system by go to 'Online Test' link below.

Packet Tracer – Identify MAC and IP Addresses (Answer Version – Optional Packet Tracer)

Answer Note: Red font color or gray highlights indicate text that appears in the Answer copy only. Optional activities are designed to enhance understanding and/or to provide additional practice.

Topology

5.3.1.3 Packet Tracer – Identify MAC and IP Addresses

Objectives

Part 1: Gather PDU Information

Part 2: Reflection Questions

Background

This activity is optimized for viewing PDUs. The devices are already configured. You will gather PDU information in simulation mode and answer a series of questions about the data you collect.

Part 1: Gather PDU Information

Note: Review the Reflection Questions in Part 2 before proceeding with Part 1. It will give you an idea of the types of information you will need to gather.

Step 1: Gather PDU information as a packet travels from 172.16.31.2 to 10.10.10.3.

1. Click 172.16.31.2 and open the Command Prompt.
2. Enter the ping 10.10.10.3 command.
3. Switch to simulation mode and repeat the ping 10.10.10.3 command. A PDU appears next to 172.16.31.2.
4. Click the PDU and note the following information from the Outbound PDU Layer tab:
   • Destination MAC Address: 00D0:BA8E:741A
   • Source MAC Address: 000C:85CC:1DA7
   • Source IP Address: 172.16.31.2
   • Destination IP Address: 10.10.10.3
   • At Device: Computer
5. Click Capture / Forward to move the PDU to the next device. Gather the same information from Step 1d. Repeat this process until the PDU reaches its destination. Record the PDU information you gathered into a spreadsheet using a format like the table shown below:

Example Spreadsheet Format

Step 2 Gather additional PDU information from other pings.

Repeat the process in Step 1 and gather the information for the following tests:

• Ping 10.10.10.2 from 10.10.10.3.
• Ping 172.16.31.2 from 172.16.31.3.
• Ping 172.16.31.4 from 172.16.31.5.
• Ping 172.16.31.4 from 10.10.10.2.
• Ping 172.16.31.3 from 10.10.10.2.

Part 2: Reflection Questions

Answer the following questions regarding the captured data:

1. Were there different types of wires used to connect devices? Yes, copper and fiber
2. Did the wires change the handling of the PDU in any way? No
3. Did the Hub lose any of the information given to it? No
4. What does the Hub do with MAC addresses and IP addresses? Nothing
5. Did the wireless Access Point do anything with the information given to it? Yes. It repackaged it as wireless 802.11
6. Was any MAC or IP address lost during the wireless transfer? No
7. What was the highest OSI layer that the Hub and Access Point used? Layer 1
8. Did the Hub or Access Point ever replicate a PDU that was rejected with a red “X”? Yes
9. When examining the PDU Details tab, which MAC address appeared first, the source or the destination? Destination
10. Why would the MAC addresses appear in this order? A switch can begin forwarding a frame to a known MAC address more quickly if the destination is listed first
11. Was there a pattern to the MAC addressing in the simulation? No
12. Did the switches ever replicate a PDU that was rejected with a red “X”? No
13. Every time that the PDU was sent between the 10 network and the 172 network, there was a point where the MAC addresses suddenly changed. Where did that occur? It occurred at the Router
14. Which device uses MAC addresses starting with 00D0? The Router
15. To what devices did the other MAC addresses belong? To the sender and receiver
16. Did the sending and receiving IPv4 addresses switch in any of the PDUs? No
17. If you follow the reply to a ping, sometimes called a pong, do the sending and receiving IPv4 addresses switch? Yes
18. What is the pattern to the IPv4 addressing in this simulation? Each port of a router requires a set of non-overlapping addresses
19. Why do different IP networks need to be assigned to different ports of a router? The function of a router is to inter-connect different IP networks.
20. If this simulation was configured with IPv6 instead of IPv4, what would be different? The IPv4 addresses would be replaced with IPv6 addresses, but everything else would be the same.

From year to year, Cisco has updated many versions with difference questions. The latest version is version 6.0 in 2018. What is your version? It depends on your instructor creating your class. We recommend you to go thought all version if you are not clear. While you take online test with netacad.com, You may get random questions from all version. Each version have 1 to 10 different questions or more. After you review all questions, You should practice with our online test system by go to 'Online Test' link below.

Suggested Scoring Rubric

There are 20 questions worth 5 points each for a possible score of 100.