how does a mac address assignment to a network card takes place

How-To Geek

What is a mac address, and how does it work.

Your changes have been saved

Email Is sent

Please verify your email address.

You’ve reached your account maximum for followed topics.

5 Things I Never Back Up to the Cloud

This all-in-one linux distro isn’t for everyone, but it cured my distro-hopping habit, verizon internet now includes discounted netflix, max, disney, and hulu, quick links, what is a mac address, how does a mac address work, how are mac addresses used, how do i find my mac address.

If you've ever tried to identify devices on a network or search for a nearby Bluetooth device , chances are you've dealt with MAC addresses. But what are they exactly, and how are they different from IP addresses?

Multiple hardware and software elements work together every day to connect us to the internet and get data to our devices. Hardware devices like routers and cables transmit the data we need, while software like border gateway protocol (BGP) and internet protocol (IP) addresses direct those data packets to and from those devices. Without both working together, we couldn't get online.

One of those critical elements is the media access control (MAC) address. MAC addresses are associated with specific devices and assigned to them by the manufacturer.

Other names used for MAC addresses include:

• Networking hardware address
• Burned-in address (BIA)
• Physical address
• Ethernet hardware address (EHA)

Wi-Fi, Bluetooth , and Ethernet connections all use MAC addresses.

MAC addresses work with the card in your device that lets it connect wirelessly to the internet, called a Network Interface Controller (NIC). MAC addresses are used to identify which device is which on your local network so that data gets sent to your computer and not your roommate's smartphone.

MAC addresses are always a 12 digit hexadecimal number, with the numbers separated every two digits by a colon or hyphen. So a MAC address of 2c549188c9e3, for example, would be displayed 2C:54:91:88:C9:E3 or 2c-54-91-88-c9-e3.

Large network adapter manufacturers like Dell and Cisco will often code their identifiers, called their Organizationally Unique Identifier (OUI), into the MAC addresses of devices they make. They're always the first six digits. Dell's, for example, is 00-14-22.

Related: What Is a Network Adapter?

When data packets from the internet hit your router, that router needs to be able to send them to the right device on its network. It does this using MAC addresses, assigning a private IP address to each network-connected device based on that device's MAC address. This is different from the IP address your internet service provider (ISP) assigns you---that's your public IP address.

Your router tracks outbound data requests so that when the data comes back, it can attach the correct private IP to the data packets, then send them along to whichever device's MAC address matches that private IP.

Devices can have more than one MAC address because they get one for every place they can connect to the internet. If your laptop has an ethernet port and Wi-Fi , for example, it would have different MAC addresses for the Wi-Fi connection and the Ethernet connection. Bluetooth also uses its own MAC address.

Related: Wi-Fi vs. Ethernet: How Much Better Is a Wired Connection?

In addition to sending your data to the right place, your wireless router also uses MAC addresses to secure your connection by only accepting traffic from devices with MAC addresses that it recognizes. This is called MAC filtering.

Related: Internet Connection Not Working? 10 Troubleshooting Tips

MAC addresses can also be used by technicians to troubleshoot connection problems on a network . Because they're unique to each hardware device, it's easier to pinpoint which piece of hardware connected to the network is sending and receiving data by looking at the MAC address. From there, they can see which device is having trouble connecting.

If you need to find the MAC address for your device, you can usually do it by going into the settings menu. You can follow our guide to finding the MAC addresses on your Windows device , whether by the Settings app or by the command prompt.

It's also easy to find the MAC address on a Mac computer . In System Preferences, click the Network icon, select the interface you want to use, then click Advanced. You'll see the MAC address listed under the Hardware tab.

Many more devices, including smart TVs, game consoles, and smartphones have their own MAC addresses that you can find .

If you want to, it's also possible to change or "spoof" your MAC address .

Related: How to Permanently Change Your MAC Address on Linux

• Cloud & Internet

Home > Articles

Networking Devices

• Jun 13, 2005

📄 Contents

• Introduction
• Network Cards
• Wireless Access Points
• Transceivers (Media Converters)

MAC Addresses

• Review and Test Yourself
• Need to Know More?
• ⎙ Print

This chapter is from the book

This chapter is from the book 

A MAC address is a unique 6-byte address that is burned into each network interface or more specifically, directly into the PROM chip on the NIC. The number must be unique, as the MAC address is the basis by which almost all network communication takes place. No matter which networking protocol is being used, the MAC address is still the means by which the network interface is identified on the network. Notice that I say network interface. That’s very important, as a system that has more than one network card in it will have more than one MAC address.

MAC addresses are expressed in six hexadecimal values. In some instances, the six values are separated by colons (:); in others, hyphens (-) are used; and in still others, a space is simply inserted between the values. In any case, because the six values are hexadecimal, they can only be numbers 0–9 and the letters A–F. So, a valid MAC address might be 00-D0-56-F2-B5-12 or 00-26-DD-14-C4-EE . There is a way of finding out whether a MAC address exists through the IEEE, which is responsible for managing MAC address assignment. The IEEE has a system in place that lets you identify the manufacturer of the network interface by looking at the MAC address.

For example, in the MAC address 00-80-C8-E3-4C-BD , the 00-80-C8 portion identifies the manufacturer and the E3-4C-BD portion is assigned by the manufacturer to make the address unique. The IEEE is the body that assigns manufacturers their IDs, called Organizationally Unique Identifiers, and the manufacturer then assigns the second half, called the Universal LAN MAC address. From the IEEE’s perspective, leaving the actual assignment of addresses to the manufacturers significantly reduces the administrative overhead for the IEEE.

As discussed, MAC addresses are expressed in hexadecimal format. For that reason, they can only use the numbers 0–9 and the letters A–F. There are only six bytes, so a MAC address should be six groups of two characters. Any other number of characters or any answer that contains a letter other than those described can be immediately discounted as an answer.

The method by which you can discover the MAC address of the network interfaces in your equipment depends on which operating system is being used. Table 3.5 shows you how to obtain the MAC address on some of the more common platforms.

Be prepared to identify the commands used to view a MAC address as shown in Table 3.5. You might be asked to identify these commands on the Network+ exam.

Table 3.5 Commands to Obtain MAC Addresses

As you work with network interfaces more, you might start to become familiar with which ID is associated with which manufacturer. Although this is a skill that might astound your friends and impress your colleagues, it won’t help you with the Network+ exam. Just knowing what does, and doesn’t, represent a valid MAC address will be sufficient on the exam.

• 🔖 Save To Your Account

Pearson IT Certification Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from Pearson IT Certification and its family of brands. I can unsubscribe at any time.

Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about Pearson IT Certification products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information

To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites; develop new products and services; conduct educational research; and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

Newsletters

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply www.informit.com/u.aspx , enter your email address in the field supplied, and click the Submit button. On the resulting page, check the box of the particular item(s) you would no longer like to receive, and click the Unsubscribe button-->email [email protected] .

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form .

Other Collection and Use of Information

Application and system logs.

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

This site is not directed to children under the age of 13.

Pearson may send or direct marketing communications to users, provided that

• Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
• Such marketing is consistent with applicable law and Pearson's legal obligations.
• Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
• Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information

If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page . If a user no longer desires our service and desires to delete his or her account, please contact us at [email protected] and we will process the deletion of a user's account.

Choice/Opt-out

Users can always make an informed choice as to whether they should proceed with certain services offered by Adobe Press. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.pearsonitcertification.com/u.aspx .

Sale of Personal Information

Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to [email protected] .

Supplemental Privacy Statement for California Residents

California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure

Pearson may disclose personal information, as follows:

• As required by law.
• With the consent of the individual (or their parent, if the individual is a minor)
• In response to a subpoena, court order or legal process, to the extent permitted or required by law
• To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
• In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
• To investigate or address actual or suspected fraud or other illegal activities
• To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
• To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
• To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact

Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice

We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020

•  View Your Cart
• 👤 Sign In
• CISSP/Cybersecurity
• Oracle/Java
• Project Management
• Exam Vouchers
• Practice Tests
• Video Courses
• Learning Options
• Deals & Promotions
• Affiliate Program
• Chapters & Articles
• Special Offers & Newsletter
• Customer Service & Tech Support
• Ordering Info
• Legal Notice
• Ordering Information
• Privacy Notice
• Do Not Sell My Personal Information
• Write For Us

© 2024 Pearson Education, Pearson IT Certification . All rights reserved.

221 River Street , Hoboken , NJ 07030

MAC Address or Ethernet Addressing Explained

Every Ethernet frame contains two addresses: source and destination. The source address represents the device that generated it. The destination address represents the recipients of the frame.

An Ethernet address is also known as a Hardware address, physical address, burned-in address, universal address, MAC address, or LAN address.

These terms define the purposes and functions of the Ethernet address. For example, the terms hardware address and physical address indicate the address belongs to an interface.

The terms MAC address and LAN address indicate the data link layer uses this address in the LAN environment.

The term burned-in address (BIA) specifies a fact that indicates a permanent MAC address has been encoded (burned into) the ROM chip on the NIC.

The term universal address indicates the address is unique in the universe.

Globally unique MAC addresses

An administrative process is followed to make each MAC address unique in the universe. A MAC address is a 6-byte-long (48-bit-long) binary number. In this number, the first 3 bytes are assigned by IEEE and the last 3 bytes are assigned by the manufacturer.

Before a manufacturer builds Ethernets, it obtains a universally unique 3 bytes code from IEEE. IEEE provides a unique 3 bytes code to every Ethernet product manufacturer.

The manufacturer uses the assigned code to generate MAC addresses for its products. In each MAC address, it uses the assigned code as the first 3 bytes. It uses the last 3 bytes to make the address unique. As a result, the MAC address of every device in the universe is unique.

The following image shows an example of this process.

For convenience, devices display MAC addresses as 12-digit hexadecimal numbers. They add periods between two hexa numbers. For example, a Cisco switch might list a MAC address as 0012.AB12.3456.

Examples of MAC addresses

Following are the example MAC addresses

0000.AB12.3456, AA12.AB12.3456, 0012:1234:45CD, CC00:AABB:CC22

• MAC stands for Media Access Control.
• Each MAC address is unique in the universe.
• MAC addresses work in the Data Link layer.
• A MAC address is locally significant.
• A MAC address is 48 bits long in binary.
• A MAC address is usually written in hexadecimal.
• An Organizationally Unique Identifier is a 3-hexa bytes code.
• IEEE assigns OUI codes to Ethernet manufacturers.
• OUI codes are unique among manufacturers.
• Manufacturers use OUI codes to generate unique MAC addresses for their products.
• In each MAC address, the first 3-hexa bytes are OUI.
• The manufacturer uses the last 3-hexa bytes to generate unique MAC addresses for every interface.

By ComputerNetworkingNotes Updated on 2023-06-17

ComputerNetworkingNotes CCNA Study Guide MAC Address or Ethernet Addressing Explained

• EtherChannel Load Distribution Explained
• Link Aggregation Control Protocol (LACP) Explained
• Port Aggregation Protocol (PAgP) Explained
• EtherChannel Manual Configuration
• EtherChannel Basic Concepts Explained

We do not accept any kind of Guest Post. Except Guest post submission, for any other query (such as adverting opportunity, product advertisement, feedback, suggestion, error reporting and technical issue) or simply just say to hello mail us [email protected]

MAC Addresses

A MAC address is a unique 6-byte address that is burned into each network interface or more specifically, directly into the PROM chip on the NIC. The number must be unique, as the MAC address is the basis by which almost all network communication takes place. No matter which networking protocol is being used, the MAC address is still the means by which the network interface is identified on the network. Notice that I say network interface. That's very important, as a system that has more than one network card in it will have more than one MAC address.

MAC addresses are expressed in six hexadecimal values. In some instances, the six values are separated by colons (:); in others, hyphens (-) are used; and in still others, a space is simply inserted between the values. In any case, because the six values are hexadecimal, they can only be numbers 09 and the letters AF. So, a valid MAC address might be 00-D0-56-F2-B5-12 or 00-26-DD-14-C4-EE . There is a way of finding out whether a MAC address exists through the IEEE, which is responsible for managing MAC address assignment. The IEEE has a system in place that lets you identify the manufacturer of the network interface by looking at the MAC address.

For example, in the MAC address 00-80-C8-E3-4C-BD , the 00-80-C8 portion identifies the manufacturer and the E3-4C-BD portion is assigned by the manufacturer to make the address unique. The IEEE is the body that assigns manufacturers their IDs, called Organizationally Unique Identifiers, and the manufacturer then assigns the second half, called the Universal LAN MAC address. From the IEEE's perspective, leaving the actual assignment of addresses to the manufacturers significantly reduces the administrative overhead for the IEEE.

The method by which you can discover the MAC address of the network interfaces in your equipment depends on which operating system is being used. Table 5 shows you how to obtain the MAC address on some of the more common platforms.

As you work with network interfaces more, you might start to become familiar with which ID is associated with which manufacturer. Although this is a skill that might astound your friends and impress your colleagues.

What is a MAC Address?

• Categories Blog , Security
• Comments 0 comment

MAC (Media Access Control) Address

The MAC address is used by the Media Access Control sublayer of the Data-Link Layer (DLC)  of telecommunication protocols.

Every  NIC   (also called LAN card) has a hardware address that’s known as a MAC, for Media Access Control. The MAC address is sometimes referred to as a networking hardware address, the burned-in address (BIA), or the physical address.

A MAC address is given to a network adapter when it is manufactured. It is hardwired or hard-coded onto your computer’s network interface card (NIC) and is unique to it. ARP (Address Resolution Protocol) translates an IP address into a MAC address.

The ARP takes data from an IP address through an actual piece of computer hardware.

Related – MAC Address vs IP Address

Tag: Layer 2

I am here to share my knowledge and experience in the field of networking with the goal being - "The more you share, the more you learn."

I am a biotechnologist by qualification and a Network Enthusiast by interest. I developed interest in networking being in the company of a passionate Network Professional, my husband.

I am a strong believer of the fact that "learning is a constant process of discovering yourself." - Rashmi Bhardwaj (Author/Editor)

Previous post

OSPF LSA TYPES

What is lan detailed explanation, you may also like.

Introduction to WatchGuard Network Security Firewall

What is “NET:ERR_CERT_AUTHORITY_INVALID” Error?

Palo Alto Cloud NGFW for Azure: Cloud Security

Leave a reply cancel reply.

Your email address will not be published. Required fields are marked *

Please enter an answer in digits: one × 3 =

Stack Exchange Network

Stack Exchange network consists of 183 Q&A communities including Stack Overflow , the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.

Q&A for work

Connect and share knowledge within a single location that is structured and easy to search.

What is the exact use of a MAC address?

I understand that IP addresses are hierarchical, so that routers throughout the internet know which direction to forward a packet. With MAC addresses, there is no hierarchy, and thus packet forwarding would not be possible. So, MAC addresses are not used for packet transfer.

I don't think it sits there for no reason. So my question is, where exactly does a MAC address come into play during a packet transfer?

• mac-address

14 Answers 14

TL;DR> MAC addresses are a low level component of an Ethernet network (and some other similar standards, such as WiFi). They allow a device to communicate with a machine on the local physical network (LAN), and cannot be routed across the Internet - because physical hardware might in theory be plugged in anywhere in the world. By contrast, IP addresses cover the whole internet, and routers use them to figure out where to send data even if it needs multiple hops to reach its destination – but they aren't helpful in interfacing with the physical hardware on your local network. If we ever found a better standard than Ethernet, it might not use MAC addresses but IP traffic from the internet could still flow across it, even if other people on the internet had never heard of it. If we ever found a better standard than IP (for example IPv6 if all the IPv4 addresses ran out), most Ethernet hardware could carry the new kind of traffic without modification – and a simple software/firmware update would fix most of the rest.

MAC addresses are required to make a local Ethernet (or wifi) network function. They allow a network device to attract the attention of a single directly connected device, even though the physical connection is shared. This can be important when thousands of devices are connected together within a single organisation. They serve no function on the wider internet.

To really understand the answer to this question, you need to understand the OSI (sometimes known as the 7-layer) model .

For communication to take place between 2 applications running on separate machines which don't have a direct physical connection, a lot of work needs to take place.

In the olden days, each application would know exactly which machine code instructions needed to be run in order to produce an appropriate signal that would reach, and could be decoded by, the application at the far end. All communication was effectively point-to-point, and software had to be written to suit the exact situation in which it was to be deployed. Obviously, that was unsustainable.

Instead of this, the problem of networking was split into layers, and each layer knew how to speak to the matching layer on a remote machine, and how to communicate with the layer beneath (and sometimes above) it on its local machine. It knew nothing at all about any other layers in place – so your web browser doesn't need to care whether it is running on a machine that uses a token ring, ethernet or wifi network – and definitely doesn't need to know what hardware the remote machine uses.

To make this work, the 7 layer model uses a system rather like nested envelopes; the application creates its data and wraps it in an envelope for the Operating System to deliver. The OS wraps this in another envelope and passes it to the Network driver. The Network driver wraps this in yet another envelope and puts it onto the physical cable. And so on.

The bottom layer, layer 1 , is the physical layer. This is the layer of wires and transistors and radio waves, and at this layer, communication is mostly just a stream of ones and noughts. The data goes everywhere that is physically connected. You plug your computer's network port into your switch using a CAT-5 cable.

Layer 2 is the Data link layer. This provides some structure to the ones and noughts, some error detection and correction capabilities, and some indication about which physically connected device (physical connections here can actually be over wifi) should pay attention to the message. This is the layer that MAC addresses come into play, and we'll come back to it later. But MAC addresses aren't the only possibility at this layer. Token ring networks, for example, need a different data link implementation.

Layer 3 is the Network layer. This is the layer that IP works at (though it isn't the only network layer protocol either), and it is this that allows computers to send a message that can get to any machine anywhere on the "network". There does not need to be a direct connection between the machines in question.

Layers 4-7 are higher level protocols. They get ever further away from the hardware and closer to the application. TCP, for example, sits on top of IP, and provides mechanisms that automatically resend messages when they go missing.

So MAC addresses work at Layer 2, and permit 2 machines that are physically connected to one another to send messages that will be ignored by other machines which share the same physical connection.

Suppose I have an application that wants to send some data to the machine with IP address 8.8.8.8

Layer 3 wraps up the data in an envelope that contains, amongst other things, the IP address 8.8.8.8 and then hands this to layer 2.

Layer 2 looks at this IP address and decides which machine that it is directly connected to is able to deal with this message. It will have a lookup table of a selection of the directly connected IP addresses together with the corresponding MAC address of the network card in that machine. This lookup table is constructed using a protocol called ARP, which lets a network card asks questions of the other directly connected devices. Ethernet reserves a special MAC address, FF:FF:FF:FF:FF:FF, which lets a device talk to all physically connected devices.

If the IP address is in the table (or can be resolved through ARP), it will wrap the Layer 3 envelope in a Layer 2 envelope with the MAC address in the new header, and then pass the whole bundle to the hardware at Layer 1. The network card with the matching MAC address will receive the message and the network driver will open the Layer 2 envelope and pass the contents up to whichever part of the operating system is expecting to receive messages at the specific IP address.

Alternatively, if the IP address isn't on the local network, the new envelope will have the MAC address of the default gateway (i.e. Router) configured for this network interface, and the hardware will transport the packet to the router.

The router notices its own MAC address in the layer 2 envelope, and opens the level 2 packet. It looks at the IP address on the level 3 envelope, and works out where the message needs to go next, which is probably going to be the router at your ISP. If the router uses NAT (or similar), it may even modify the level 3 envelope at this point, to keep your internal IP addresses private. It will then wrap the level 3 envelope in a new level 2 envelope that is addressed to the ISP's router's MAC address, and send the message there.

This process of removing the outer envelope and wrapping the contents in a new envelope addressed to the next step in the chain will continue until the message reaches the destination machine.

The envelopes will then continue being ripped off as the message walks back up the layers until it finally reaches its intended recipient, which will be an application somewhere which, hopefully, will know what to do with the message – but will have no idea how the message got there nor indeed all the steps required to get the response back to the original machine.

But it all works, almost like magic!

Note that network switches can use MAC addresses to optimise the flow of network traffic. While an ethernet hub simply forwards all incoming traffic to all of its ports, by contrast a switch can forward traffic only to the single port that the packet's destination MAC address is connected to. This increases the effective bandwidth of the network; by targeting specific ports, the switch avoids forwarding traffic on unnecessary segments of the network. The switch will use either ARP or packet sniffing to identify which devices are connected to which port. Switches completely ignore the contents of the Layer 2 packets.

• Hi! thanks for the answer. As far as I've read, your answer is the best. It would be awesome if you could include some more concepts like ARP and NAT within your scenario. –  Vishnu Vivek Commented Jul 26, 2013 at 1:09
• 1 Added reference to ARP and network Switches. I don't think NAT has anything to do with MAC addresses, being a layer 3 function... –  Bill Michell Commented Jul 26, 2013 at 8:39
• @BillMichell: In IPv6 the MAC or other local ('hardware') ID can be used to compose the IP. –  Luciano Commented Jul 26, 2013 at 15:37
• The answer is community Wiki. You can probably edit it to include this additional information if you think it will help answer the OP's question. –  Bill Michell Commented Jul 26, 2013 at 15:48
• This needs a TL;DR. –  AJMansfield Commented Jul 26, 2013 at 16:33

What are MAC addresses used for?

MAC addresses are the low level basics that make your local ethernet based network work. Local means that the network devices are either directly connected through a cable or by WiFi or over a network hub or network switch.

Network cards each have a unique MAC address. Packets that are sent on the ethernet are always coming from a MAC address and sent to a MAC address. If a network adapter is receiving a packet, it is comparing the packet's destination MAC address to the adapter's own MAC address. If the addresses match, the packet is processed, otherwise it is discarded (exception follows in next paragraph).

There are special MAC addresses, one for example is ff:ff:ff:ff:ff:ff, which is the broadcast address and addresses every network adapter in the network. If a network adapter is receiving a packet sent to the broadcast address, then it is processing it.

How do network switches influence the packet flow?

A hub has no intelligence and just connects the wires from all the attached network cables, so packets sent on the network are received by every other connected network adapter. Network switches have some logic inside and can forward or drop packets.

When a network switch receives a packet on one port it needs to know to which port(s) to forward the packet. Broadcast MAC address is simple, that means just forwarding to all other ports. Individual MAC addresses require more work. If the destination is an individual MAC address, then it forwards the packet only to the port where the adapter with this MAC address is connected. How does the switch know that port? Because it examines all received packets and per port builds a table with the source MAC addresses seen in the packets received on that port. These entries are valid for some time and then discarded if no more packets are received from that MAC address. And what if the MAC address is not known (yet)? Then the switch needs to send the packet to all other ports, like it does for the broadcast MAC address.

With MAC addresses you can only reach what is directly connected/wired. If you want to connect different networks you need more structure and then IP comes into play. The name already says it IP, internet protocol, a protocol to connect networks.

How do IP addresses and MAC addresses work together?

IP is a protocol that is used on a layer above ethernet. Another protocol for example would be IPX. IP allows connecting of different local networks and thus forming a corporate network or the global internet. If IP packets are sent, then we still have the MAC addresses of sender and receiver in the packet and additionally the IP addresses of the sender and the receiver.

Now when your computer wants to send a packet to some IP address x.x.x.x, then the first check is if the destination address is in the same IP network as the computer itself. If x.x.x.x is in the same network, then the destination IP must be in the local ethernet and can be reached directly. We just need to know the MAC address where to send the packet to. If the destination IP is not in our own network, then the packet needs to be sent to the configured router. Again we need to know the MAC address where to send the packet to.

As we see there must be some mechanism to retrieve the MAC address for an IP address in the local network. That mechanism is the address resolution protocol (ARP).

Once the sender has retrieved the MAC address of the next hop (either local destination or local configured router), he writes that target MAC address into the packet and sends the packet.

How does ARP work?

ARP itself is a protocol above ethernet, like IP or IPX. When a device wants to know the MAC address for a given IP address, it sends a packet to the broadcast MAC address asking "Who has IP address y.y.y.y?" All devices receive that packet, but only the one with the IP address y.y.y.y will respond with a packet "It's me." The asking device receives the answer and now knows that the source MAC address of the ARP packet is the right MAC address to use. Of course the result will be cached, so the device does not need to resolve the MAC address every time.

There is no routing based on MAC addresses. Low level ethernet and MAC addresses can only reach every device on the same network (cabled or wireless). If you have two networks with a router in between you cannot have a device in network A send a packet to the MAC address of a device in network B. No device in network A has the MAC address of the device in network B, so a packet to this MAC address will be discarded by all devices in the network A (also by the router).

Routing is done on IP level. It is done by routers which have multiple network adapters (at least two). Simply seen the router is just doing what I described above in the section "How do IP addresses and MAC addresses work together?". The router will receive packets for its own MAC address but for a different IP address. He will then check if he can directly reach the target IP address (on another network adapter). If so, he sends the packet to the target. Otherwise the router itself also has an upstream router configured and will send the packet to that router.

Of course you can have multiple routers configured. Your home router will only have one upstream router configured, but in the internet backbone the big routers have big routing tables so they know the best ways for all packets.

Other use cases for MAC addresses

Wireless access points often use MAC addresses for access control. They only allow access for known devices (MAC address is unique and identifies devices) with the correct passphrase.

DHCP servers use the MAC address to identify devices and give some devices fixed IP addresses.

• 17 +1 for actually answering the question in a way that people who don't already know the answer can understand. –  fluffy Commented Jul 24, 2013 at 17:51
• I can't help but feel the urge to create an awesome infographic/diagram somehow, the way MAC/IP interact is quite interesting! –  NRGdallas Commented Jul 24, 2013 at 21:56
• 1 nice answer just a detail: MAC addresses are also used for non Ethernet devices and was you describe basically holds for any data-link layer used with an IP stack –  kriss Commented Jul 25, 2013 at 4:23
• Worth noting about Wi-Fi MACs: While they are generally unique and can be used to identify devices, they're easy to spoof and sent in the clear over the air. If there is no other encryption/authentication used on the connection, or if the other encryption/authentication mechanism(s) are weak (e.g.: WEP), it is very trivial for an attacker to impersonate an authorized device and join the network. –  Iszi Commented Sep 4, 2013 at 20:50
• 2 @Rick You are right, the destination IP for a connection does not change. But in the cited paragraph I was talking about the direct destination of the packet - which might be the router, and the router might change during the connection. Regarding your second comment I changed the text to "source MAC address of the ARP packet". I hope that is more clear. –  Werner Henze Commented Jul 15, 2019 at 9:01

The MAC-Address (Media Access Control address) in general is the identifier of devices in a network. So every NIC (network interface controller found in a router, PC, network-printer, server etc.) have MAC addresses. Some servers have more than one network card built in and therefore have multiple MAC addresses. The MAC address is 6 Bytes long (6 octets). Left is the most significant Byte and right the least significant Byte. As you can see in the picture below, the first 3 Bytes are the Organizationally Unique Identifier . This indicates the manufacturer who made this device.

Here's a list of Organizationally Unique Identifier : Standards.ieee.org

Here's an alternative to the above: MAC-Vendor-Lookup

A few examples of common known manufacturers:

• 00-05-5D (D-Link Systems Inc.)
• 00-09-5B (Netgear Inc.)
• 00-E0-4C (Realtek Semiconductor Corp.)
• 00-E0-4F (Cisco Systems Inc.)
• 00-E0-64 (Samsung Electronics)

The last 3 Bytes (3 octets) are randomly assigned by the manufacturer.

As pjc50 stated correctly the MAC address in an Ethernet network helps the switches decide which packet to send where. There is also a Broadcast-MAC-Address. ff:ff:ff:ff:ff:ff is used for the Broadcast-MAC-Address. Note that the MAC-Address can be changed so be careful using it as a definite device identifier! The MAC-Address is also used with the ARP (Address Resolution Protocol) protocol. So how it works is, PC A sends a ARP-Request to PC B with its own IP-Address, MAC-Address, the IP-Address of the receiver and the broadcast address mentioned above (ff:ff:ff:ff:ff:ff). After that PC B checks if the Packet was send to him or not. If yes, then PC B sends its own MAC-Address, IP-Address, the MAC-Address of the receiver and the IP-Address of the receiver back. The other devices discard the packet.

Both PC A and B usually save the successful connection in the so called ARP-Cache. The way the PCs save the connection differs from device to device. If you don't know the IP-Address then you can get the IP-Address with the Reverse Address Resolution Protocol (RARP). With RARP the device contacts a central client and asks it for the IP-Address. But this method is hardly used nowadays.

The following technologies use the MAC-48 identifier format:

• 802.11 wireless networks
• IEEE 802.5 token ring
• most other IEEE 802 networks
• ATM (switched virtual connections only, as part of an NSAP address) Fibre Channel and Serial Attached SCSI (as part of a World Wide Name)
• 4 More accurately than "every Device (...) have MAC-Addresses.", every NIC has A MAC address . (Not taking the ability to set a custom MAC address into account.) Not all printers have network cards built-in, and many servers have more than one network card and thus more than one MAC address. –  user Commented Jul 24, 2013 at 9:53
• 2 Lets Say PC-1 sends a Packet to PC-2. Now the Switch only reads the MAC-Address of PC-1 and saves it into a table. If you want more Info on how it works, read this: How LAN Switches Work :) –  Meintjes Commented Jul 24, 2013 at 10:08
• 3 Another point is that the MAC address is how the NIC decides what to discard and what to send to the processor for handling. An Ethernet frame encountered on the wire has its destination MAC address XOR'd with the NIC MAC address and if the result is all 0s then it's a frame intended for this NIC. –  bbayles Commented Jul 24, 2013 at 12:20
• 7 -1: The question asked how MAC addresses are used, not what a MAC address is. The only part of your answer that addresses the question is the bullet list at the end, and it doesn't go into much detail. –  Kevin Commented Jul 24, 2013 at 15:23
• 4 The picture is taken from wikipedia: en.wikipedia.org/wiki/File:MAC-48_Address.svg , pictures licensed under creative commons must be attributed to their authors when used. –  Étienne Commented Jul 24, 2013 at 21:27

They are used for packet transfer: on an Ethernet network, there are a number of devices, and the MAC address specifies which device should receive the packet. Ethernet switches will use it to choose which port to send out a received packet on.

• 5 May be interesting to note that Ethernet originally was a bus medium, where all machines physically shared the same media (this is still true for wireless networks). So logically it works like that. –  LawrenceC Commented Jul 24, 2013 at 11:29
• and still true for networks that still use hubs :) –  Doon Commented Jul 24, 2013 at 18:00
• henceforth switches are just a facility (really became wide spread with RJ-45 LANs) we can and do have IP networks without them (using hubs or 802.11) –  kriss Commented Jul 25, 2013 at 4:30

Forget hierarchy in this case, it not a very important issue.

MAC address are addresses for layer 2 (link layer) in the ISO/OSI or TCP/IP models. IP addresses are from layer 3 (Network layer) in the same models.

In a layer 2 network, for instance a common Ethernet network, there exists a collision domain, where all the equipment connected can receive all the frames (layer 2 unit data) from any endpoint. But nobody outside the network can receive these frames. MAC addresses are addresses in these domains.

Packets are the layer 3 unit data, typically, IP packets. They travel through one or more collision domains. IP addresses are the addresses in this domain.

Switches are layer 2 devices and forward frames using MAC addresses tables. Routers are layer 3 devices and they forward packets using IP addresses tables.

Ethernet assumes the other computer (the other MAC) it wants to talk to is directly reachable out of its network adapter. IP does not. IP assumes it can reach any other IP in the entire world and that if it can't reach it on the current subnet, a router will carry it there, NAT notwithstanding. The notion of gateways does not exist in Layer 2 or Ethernet.

If you have a number of machines connected to a switch, and will not ever need to trade traffic with other networks/the Internet via a router, then you really don't need to have IP up and running. Of course, an application would have to implement or provide their own protocol above layer 2, since pretty much all OSes and applications assume you always want to use TCP/IP.

Always remember the 'Internet' in IP means 'internetworking' meaning really it is concerned with getting traffic between networks more than in a network, though obviously it can be (and is) used for that too.

• The first paragraph is the perfect answer! Illuminating! –  Milind R Commented May 2, 2015 at 20:05

The MAC address is used on the physical transfer. An ethernet adapter does not know anything about IP. So the ethernet adapter uses the MAC address to address the receiver of the data packet.

If the ethernet adapter would know anything about IP then we have to upgrade all our firmware to switch to a new protocol (like IPv4 to IPV6).

Also the MAC address has some information in it about the manufacturer in it.

• 3 Routers do not use the MAC address to route anything. They use IP addresses. Hubs copy traffic unmodified out of their ports, but this would be called bridging, since the traffic does not traverse over a different network, but over the same network. –  LawrenceC Commented Jul 24, 2013 at 11:21

It is used when the ARP (Address resolution protocol) for IPv4 or the NDP (Neighbor Discovery Protocol) for IPv6, translates the IP Addresses into MAC addresses to determine which unique host the frames should be sent to.

• This is pretty close, but it doesn't cover all the usage. That's how a MAC relates to TCP/IP, but a MAC is used for far more than just that. This is the first answer I'm not giving a -1 to though (working from the bottom of the page up). –  Mark Henderson Commented Jul 25, 2013 at 0:38
• @Mark Henderson Thanks for the criticism. Well I just tried to answer the question How MAC addresses were used in packet transfer and then I assumed it was on an Ethernet level. And yes it is a simple answer, but I'm answering on a level that suits my own level :) –  Jesper Jensen Commented Jul 25, 2013 at 11:54

To complete other's answers, I would add that MAC address is even more critical for routers than for switches. What I mean by more critical is that switches are not really necessary for IP network to exists. Il you look 20 years backwards (before RJ-45) Local IP networks worked perfectly without switches non routed ethernet networks were simply connecting devices on the same wire, (have a look to X base-T ethernet technology for instance).

On the other hand IP networks were invented to support routing and relies on MAC and IP addressing schemes.

Routing packets in IP networks means that when the target machine can't be accessed directly it will first be sent to another machine (the gateway) that is nearer to the final IP target.

In terms of network packet headers it means that a packet sent to a gateway will have as target in the ethernet level header the MAC address of the gateway, the IP level header being left unchanged.

You should also notice that MAC addresses usually means nowaday either MAC-48 (physical device address) or EUI-48 (logical device address) or even the 8 bytes EUI-64 addresses used in larger networks. Historically MAC was invented by Xerox for Ethernet technology and later reused for other network transports technologies (802.11, Bluetooth, FibreChannel, BlueTooth) needing to identify a device.

As I said you can use another layer-2 instead of ethernet, but most uses a MAC address as network identifier and the underlying MAC/IP correspondance scheme holds and you can still use ARP. As far as I know all IP stacks relies on correspondances table between MAC addresses and IP Addresses.

Some other kinds of device nodes identifiers exists for non IP Stacks. For instance X.25 does not relies on MAC addresses, but on virtual channels established on a per connection basis, or ATM Devices are identified in ATM networks using SNPAs. But neither X.25 or ATM are IP stacks (and even ATM uses MAC addresses format as parts of it's SNA, rough equivalent of an IP address for ATM).

• Routers don't care about MAC addresses. They do care about the subnet assignment to each of their at least 2 NICs, but not really about the MAC addresses. They forward (i.e. copy) traffic from one IP to another, not from an IP to a MAC or anything like that. –  LawrenceC Commented Jul 24, 2013 at 11:19
• 4 @ultrasawblade, your statement is absurd . If a router is connected to an Ethernet network, then it must communicate using the Ethernet protocol. IP packets will be encapsulated in the Ethernet Frame. Which means knowing the mac addresses of all the **directly Ethernet hosts ** systems is an absolutely required. A layer 3 device doesn't magically just communicate on a layer 3 protocol, it must encapsulate the layer 3 protocol within a layer 2 protocol, which is then transmitted over the layer 1 medium. –  Zoredache Commented Jul 24, 2013 at 23:34
• 3 I disagree with your first sentence - they are not "more critical" for routers than switches - they are all of equal importance throughout the entire Ethernet network. –  Mark Henderson Commented Jul 25, 2013 at 0:34
• 1 You could replace the underlying layer 2 with something entirely different (though I don't know what) and IP will still work the same. The IP protocol (Layer 3) doesn't care if the individual hosts are addressed beneath by MAC or some other scheme. Of course there is need to maintain IP to MAC mapping - but it's difficult to know if ARP really "belongs" to Layer 3 or Layer 2. The point is the layer 2 protocol doesn't have to be Ethernet and IP doesn't care/need to know what the Layer 2 protocol is. –  LawrenceC Commented Jul 25, 2013 at 2:43
• 2 @Mark Henderson: as I'm old I remember a time when there wasn't any switches around. They are not really a critical piece of equipment IP networks can works without switches. Switches merely used a preexisting data network layout. If we currently have them ubiquitously around is a consequence of RJ point-to-point technology replacing old buses. In other words: MAC addresses were not invented for making the switches work. On the other hand IP networks were invented for routing purpose, hence MAC to IP relationship is critical. –  kriss Commented Jul 25, 2013 at 4:41

Think back to the pre-switch days (hubs).

If people are computers, then the MAC address is their name.

Pretend lots of people (the computers) are on the same telephone call. Everyone is talking at the same time.

YOU (one computer) hear ALL of this chatter, but you don't know what you should listen to, UNTIL someone says your name (your MAC address) at the start of a sentence (a packet).

"FRED, THERE IS ICE CREAM!"

Of course, you also listen to sentences sent to the broadcast address . Just consider that to be someone yelling,

"EVERYONE, THERE IS ICE CREAM!"

As more people (computers) got on the conference call, the more you have to filter out. Technology advanced and switches allowed us to talk directly to one person (computer/MAC) so that they wouldn't have to work so hard to filter out all that noise (and to free more bandwidth).

IP is very similar in the basic analogy, but it has more features and layers on top of MAC addressing. Layers 2 and 3 in the OSI Model , respectively.

• You don't need to think back to pre-switched days. MAC addresses are alive and well and used in every single packet that leaves your Ethernet adapter today , right now. –  Mark Henderson Commented Jul 25, 2013 at 0:33
• Very true. But it helps with the analogy. And the NICs still behave the same way. –  Randy James Commented Jul 25, 2013 at 13:20

The MAC address is necessary because there are multiple addresses attached to the "bus" (the Ethernet network). A sender needs to be able to identify the receiver, as well as identify itself to the receiver.

All hardware buses need addressing, because multiple senders and receivers share the same wires, and messages have to go to specific receivers, and also identify the originating senders.

I2C, PCI, Ethernet, you name it.

We have multiple addresses in inter-networking (IP address and hardware address) because a hardware-level address is only local to a particular physical network. As a datagram travels from network to network, it tends to keep its network level address, but it changes hardware addresses numerous times along the way. When going over some networks, it might not have a hardware address at all, and in some other ones it might have a hardware address which is not an ethernet MAC. (Network addresses can be rewritten by a NAT gateway, of course, but hardware addresses are stripped and replaced with different ones each time a packet crosses a router.)

In the old days networks were shared buses. Each networked device connected to the same wire, or to a hub which meant that every packet you sent out was received by every device on the network.

The networking software was simpler then. Every device had a MAC address, which was guaranteed to be unique. It didn't need to be anything else - all it did was make sure that no two devices on the same network had the same address.

If your device wanted to talk to another device it would send out a packet with the recipient's MAC address, and the recipient would pick it off the network. All the other devices would ignore it - it wasn't addressed to their MAC address.

Over time people attached too many devices to the network, and they couldn't keep up with the traffic, so they started separating networks, and would attach two networks with switches. These switches had huge tables telling them which MAC addresses where on each networks. If they saw a packet on one network addressed to a MAC address on the other network, they would copy the message to the other network. They wouldn't copy all the messages, though, just the ones that needed to go to the other network.

This reduced congestion and allowed more devices to be networked, and more overall traffic to be handled. This is a packet switched network .

However it didn't solve all the problems, and suffered one huge disadvantage - as the switch tables got bigger, networks slowed down. If you connected 5,000 machines to 50 different networks all interconnected with switches, each switch had to learn all 5,000 MAC addresses and route packets based on that.

That wasn't a big deal until people from different institutions, like universities, wanted to connect their networks together, and the tables required would have been tremendous. Keeping track of a few hundred thousand MAC addresses today doesn't seem like a big deal, but in the 1970's when this was occurring the switches were computers themselves, with limited memory and speed, and keeping track of and quickly switching packets for a few hundred was a problem.

The solution was going to an IP network, and using routers. This is built on top of the MAC address based switched packet network. Rather than raw data, the packets now contain an IP packet - a packet within a packet.

Now larger networks are connected with routers. These wait until they see a packet with their MAC address, then they take the IP packet out and examine the IP address. They then re-wrap the IP packet into another packet with a new MAC address recipient on it and send it on a new network. That MAC address is probably to another router on the new network, but it could also be the machine with the IP address.

In today's networks you rarely see hubs and buses (except in wireless networks, where the medium is inherently shared) and instead my machine connects directly to a switch, which them connects to a router.

My machine has a variety of algorithms and protocols so it knows how the network is set up.

If I send an IP packet out to a machine on my local network, my machine will put it inside a packet with the correct MAC address. The switches will switch it to the correct network locally, and the machine it is destined for will receive it because it has the right MAC address. It will them take out the IP packet and double check that the IP address is also intended for it, and act accordingly.

If i send out an IP packet intended for a machine somewhere else on the internet, my machine knows to send it to the router, so it puts it inside a packet with the router's MAC address. It's again switched locally in my network until it hits the network the router is on, then the router takes it, pulls the IP packet out, examines the IP packet, and based on its knowledge of the internet, it sends it to another router on another network, wrapping it in a packet with the MAC address for the intended router or destination computer.

There are a lot of little details I've glossed over, and some truly interesting algorithms and protocols in play that make everything work, but that is the basic story of what the MAC address does for us, even today.

• 1 You started off well, but you lost it in the middle where you start talking about interconnected networks. Switches were not common until the 90's but routing existed 20 years prior to that. –  Mark Henderson Commented Jul 25, 2013 at 0:27

Bill Michell's answer is thorough and complete, but for the sake of having a tl;dr answer, IP address always identifies the final destination but we need a way to send a packet hop by hop to the final destination. For the next hop to be able to pick the right frame in a shared pool (e.g. Ethernet), mac address is the solution.

The root difference is that MAC is assigned by the manufacturer at manufacturing time, while IP address are assigned at connection time.

MAC is necessary because it can be used to identify a device before connecting to the network; however because it is statically assigned, it is pretty much distributed randomly, so it is unsuitable for efficient routing over more than a single network (doing so would require every device on the planet to have a huge routing table to all other devices on the planet). Therefore IP address are necessary because it is assigned at connection time, and the way its assigned allows more efficient long-distance routing (with IP, most devices only need to know its adjacent networks).

If there is only IP address, then devices that haven't been assigned an IP address won't be able to tell which message are meant for them. How would you determine that this DHCP is meant for you and not someone else also requesting address assignment at around the same time?

Of course MAC are also used for other parts of packet sending, but most of those uses are pretty much incidental and can (at least in theory) be replaced by dynamically assigned number (e.g. IP address).

• +1 for why we didn't just continue using MAC addresses. –  deed02392 Commented Jul 24, 2013 at 16:17
• 3 First paragraph is technically correct, but that's not the root difference. The root difference is that a MAC belongs to Ethernet, and an IP belongs to TCP/IP. You can run TCP/IP over multiple Layer 2 protocols (ATM, for example), and there is more than just TCP/IP that runs over Etherhet. There is no such thing as "before connecting to the network", but there is "Before getting an IP address from DHCP". But the MAC is still used after then - as it sits on a different layer in the OSI model. The last paragraph is downright wrong - there is no replacement for a MAC address in networking. –  Mark Henderson Commented Jul 25, 2013 at 0:32
• @MarkHenderson: My point is that MAC belonging to Ethernet and IP to TCP/IP is pretty much a historical accident; theoretically, if we redesigned the entire internet stack from scratch (and ignore OSI and compatibility with other networks), it would be possible to replace most uses of factory-assigned number (e.g. MAC) with dynamically-assigned number (e.g. IP), except that there are a number of packets that need to be sent/received before a dynamically-assigned number can be acquired, which is why a factory-assigned globally unique identifier is necessary. –  Lie Ryan Commented Jul 25, 2013 at 0:54
• @MarkHenderson: IMO, saying that we need MAC and IP because MAC is layer 2 and IP is layer 3 is just like saying "we need it because we had designed internet to be that way", it misses the point and gives no useful information whatsoever. What I'm answering here is why both factory-assigned and dynamically-assigned identifier are necessary due to the nature of the problem, and what entails from an internet stack without either (loss of routing efficiency for no dynamically-assigned ID and difficulty of uniquely addressing a device before dynamic ID assignment for no factory-assigned ID). –  Lie Ryan Commented Jul 25, 2013 at 1:07
• @LieRyan, Actually we can change our PC's MAC address....... –  Pacerier Commented Apr 6, 2015 at 15:52

You must log in to answer this question.

Not the answer you're looking for browse other questions tagged networking ip routing mac-address ..

• Featured on Meta
• Upcoming sign-up experiments related to tags

Hot Network Questions

• How to make sure to only get full frame lenses for the Canon EF (non-mirrorless) mount?
• Would a spaceport on Ceres make sense?
• Could Kessler Syndrome be used to control the temperature of the Earth?
• Liquid exited the jar during canning, is this safe to use
• Short story about a boy living on a fake tropical island / paradise planet, who was actually an adult CEO but didn't remember it
• Can a unique position be deduced if pieces are replaced by checkers (can see piece color but not type)
• book series about kids in ancient greece
• New faculty position – expectation to change research direction
• Who is a "sibling"?
• If a reference is no longer publicly available, should you include the proofs of the results you cite from it?
• Fireball or fire spells vs. Sleet Storm
• What is the explicit list of the situations that require RAII?
• Does John 14:13 mean if we literally pray for anything God will act?
• Issues with my D&D group
• Frames given by SciDraw package are not closed
• Why inductor don't discharge completely even when the duty cycle is 50%?
• 4-pin 12 V PC fan - manual speed control
• Are there really half-a billion visible supernovae exploding all the time?
• What is the purpose of the M1 pin on a Z80
• What does it mean for observations to be uncorrelated and have constant variance?
• Universal property of tensor products
• Is it unethical to have a videogame open on a personal device and interact with it occasionally as part of taking breaks while working from home?
• Cut and replace every Nth character on every row
• Derivative of the Score Function in Fisher Information