What protocol can be used by a host on a network to find the MAC address of another device based on an IP address group of answer choices?

• Ping the device you want to find a MAC address for using the local network address.
• Enter the ARP command with a "-a" flag.
• Look for the IP address in the results. The Mac address is next to the IP address.

This article explains how to find a MAC address with an IP address using the command line utility ARP. It also covers additional information about checking your router's connection data for an IP address.

In Windows, Linux, and other operating systems, the command line utility ARP (Address Resolution Protocol) shows local MAC address information stored in the ARP cache. However, it only works within the small group of computers on a local area network (LAN), not across the internet.

ARP is intended to be used by system administrators, and it is not typically a useful way to track down computers and people on the internet.

TCP/IP computer networks use both the IP addresses and MAC addresses of connected client devices. While the IP address changes over time, the MAC address of a network adapter always stays the same.

Using ARP, each local network interface tracks both the IP address and MAC address for each device it has recently communicated with. Most computers let you see this list of addresses that ARP has collected.

Here is one example of how to find a MAC address using an IP address.

1. Start by pinging the device you want the MAC to address for. Use a local address. If your network is 10.0.1.x, use that number to ping. For example:

   ping 192.168.86.45
   

2. The ping command establishes a connection with the other devices on the network and shows results like this:

   Pinging 192.168.86.45 with 32 bytes of data:Reply from 192.168.86.45: bytes=32 time=290ms TTL=128Reply from 192.168.86.45: bytes=32 time=3ms TTL=128Reply from 192.168.86.45: bytes=32 time=176ms TTL=128Reply from 192.168.86.45: bytes=32 time=3ms TTL=128
   

3. Enter the ARP command with a "-a" flag to get a list that shows the MAC address of the device you pinged:

   arp -a
   

4. The results may look something like this but probably with many other entries.

   Interface: 192.168.86.38 --- 0x3 Internet Address Physical Address Type 192.168.86.1 70-3a-cb-14-11-7a dynamic​ 192.168.86.45 98-90-96-B9-9D-61 dynamic 192.168.86.255 ff-ff-ff-ff-ff-ff static 224.0.0.22 01-00-5e-00-00-16 static 224.0.0.251 01-00-5e-00-00-fb static
   

5. Find the device's IP address in the list. The MAC address is shown right next to it. In this example, the IP address is 192.168.86.45, and its MAC address is 98-90-96-B9-9D-61.

To find the MAC address of the device connected to your router—assuming you can access the router's administrative control panel—log in and check for connected devices. Each active device, as well as recently connected devices, should list the local IP address as well as the MAC address.

There's another method used to find and change the MAC address of the computer you're currently using, which involves using the ipconfig /all command in Windows.

A single device can possess multiple network interfaces and MAC addresses. A laptop computer with Ethernet, Wi-Fi, and Bluetooth connections, for example, has two or sometimes three MAC addresses associated with it, one for each physical network device.

Reasons to track down the MAC address of a network device include:

• To set up MAC address filtering on a router to restrict local network access to only those devices whose addresses match a list of presets.
• To determine the device's manufacturer (first half of the address) and serial number (second half of the address) for service. It's important to note that the second half of the address is not always the serial number, so it might not work for warranty requests.
• To masquerade (spoof) the identity of a different device. MAC addressing spoofing can be used legitimately to register a home network gateway device with an internet provider. It can also have malicious intent, such as defeating the MAC address filtering feature to break into the network.

It isn't usually possible to look up MAC addresses for devices outside a person's physical reach. It is often impossible to determine a computer's MAC address from its IP address alone because these two addresses originate from different sources.

A computer's hardware configuration determines its MAC address, while the network configuration it is connected to determines its IP address.

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App SecurityProtocolsThreats

Address Resolution Protocol (ARP) is a protocol that enables network communications to reach a specific device on the network. ARP translates Internet Protocol (IP) addresses to a Media Access Control (MAC) address, and vice versa. Most commonly, devices use ARP to contact the router or gateway that enables them to connect to the Internet.

Hosts maintain an ARP cache, a mapping table between IP addresses and MAC addresses, and use it to connect to destinations on the network. If the host doesn’t know the MAC address for a certain IP address, it sends out an ARP request packet, asking other machines on the network for the matching MAC address. 

The ARP protocol was not designed for security, so it does not verify that a response to an ARP request really comes from an authorized party. It also lets hosts accept ARP responses even if they never sent out a request. This is a weak point in the ARP protocol, which opens the door to ARP spoofing attacks.

ARP only works with 32-bit IP addresses in the older IPv4 standard. The newer IPv6 protocol uses a different protocol, Neighbor Discovery Protocol (NDP), which is secure and uses cryptographic keys to verify host identities. However, since most of the Internet still uses the older IPv4 protocol, ARP remains in wide use.

What is ARP Spoofing (ARP Poisoning)

An ARP spoofing, also known as ARP poisoning, is a Man in the Middle (MitM) attack that allows attackers to intercept communication between network devices. The attack works as follows:

1. The attacker must have access to the network. They scan the network to determine the IP addresses of at least two devices⁠—let’s say these are a workstation and a router. 
2. The attacker uses a spoofing tool, such as Arpspoof or Driftnet, to send out forged ARP responses. 
3. The forged responses advertise that the correct MAC address for both IP addresses, belonging to the router and workstation, is the attacker’s MAC address. This fools both router and workstation to connect to the attacker’s machine, instead of to each other.
4. The two devices update their ARP cache entries and from that point onwards, communicate with the attacker instead of directly with each other.
5. The attacker is now secretly in the middle of all communications.

The ARP spoofing attacker pretends to be both sides of a network communication channel

Once the attacker succeeds in an ARP spoofing attack, they can:

• Continue routing the communications as-is⁠—the attacker can sniff the packets and steal data, except if it is transferred over an encrypted channel like HTTPS. 
• Perform session hijacking⁠—if the attacker obtains a session ID, they can gain access to accounts the user is currently logged into.
• Alter communication⁠—for example pushing a malicious file or website to the workstation.
• Distributed Denial of Service (DDoS)⁠—the attackers can provide the MAC address of a server they wish to attack with DDoS, instead of their own machine. If they do this for a large number of IPs, the target server will be bombarded with traffic.

How to Detect an ARP Cache Poisoning Attack

Here is a simple way to detect that a specific device’s ARP cache has been poisoned, using the command line. Start an operating system shell as an administrator. Use the following command to display the ARP table, on both Windows and Linux:

The output will look something like this:

If the table contains two different IP addresses that have the same MAC address, this indicates an ARP attack is taking place. Because the IP address 192.168.5.1 can be recognized as the router, the attacker’s IP is probably 192.168.5.202.

To discover ARP spoofing in a large network and get more information about the type of communication the attacker is carrying out, you can use the open source Wireshark protocol.

ARP Spoofing Prevention

Here are a few best practices that can help you prevent ARP Spoofing on your network:

• Use a Virtual Private Network (VPN)⁠—a VPN allows devices to connect to the Internet through an encrypted tunnel. This makes all communication encrypted, and worthless for an ARP spoofing attacker.
• Use static ARP⁠—the ARP protocol lets you define a static ARP entry for an IP address, and prevent devices from listening on ARP responses for that address. For example, if a workstation always connects to the same router, you can define a static ARP entry for that router, preventing an attack.
• Use packet filtering⁠—packet filtering solutions can identify poisoned ARP packets by seeing that they contain conflicting source information, and stop them before they reach devices on your network.
• Run a spoofing attack⁠—check if your existing defenses are working by mounting a spoofing attack, in coordination with IT and security teams. If the attack succeeds, identify weak points in your defensive measures and remediate them.