As long as you are not a modern illiterate, you must have heard of IP addresses. If you're familiar with networking communications, you probably know that every device has another ID number — MAC address. This article will focus on the MAC number of the most significant data transmission equipment in telecoms — switch MAC address. After reading this post, the author hopes you will have a comprehensive knowledge basis of MAC ID and can answer the frequently asked questions on switch MAC addresses.
What is MAC Address?
Besides the switch MAC address, we can find device MAC addresses in almost all networking communication hardware, such as computer MAC address, iPhone MAC address, router MAC address. To understand the switch MAC address, first, let's have an overview of the MAC ID address.
What is MAC Address in Networking?
MAC address stands for media access control address. One also calls it a hardware address, physical address, LAN address, or Ethernet address. IEEE 802 stipulates that the MAC address is 6 bytes (48 bits) in binary numbers, and written in the format of 12 hexadecimal digits. The 12 digits are presented as Arabic numerals (0 to 9) and English letters (a to f, or A to F). MAC Ethernet address consists of two parts: the first 6 digits are the manufacturer's organizationally unique identifier (OUI) and the last 6 digits stand for the serial ID of the network interface controller (NIC).
What Does a MAC Address Look Like?
These numbers are 12 hexadecimal digits (say 00015a0053af) but may be presented in different MAC address formats. Most devices' physical addresses are written in colon Hexadecimal notation, and some are in hyphen Hexadecimal notation or period-separated Hexadecimal notation. For instance, a computer MAC number is usually separated into six 2-digit pairs by colons or hyphens, say, 00:01:5a:00:53:af or 00-01-5a-00-53-af. A Cisco system network switch MAC address is usually separated into three groups by periods after every four digits, say 38f9.d329.a785.
What is a MAC Address Used for?
A media access control address is an identification number assigned to a NIC to locate a networking device port. That is to say, a switch with multiple ports connected to the network, each port has its own unique media access control address identifier. Therefore switch has a dynamic MAC address table that remembers all physical addresses of interfaces connected to it, not only the base Ethernet switch MAC address. With the memoried address, the switch can precisely locate the assigned message where to be sent.
MAC Address vs IP Address: What's the Difference & What Makes MAC Count?
Both MAC address and IP address are unique identifiers addressed to each device in the network. It is because of these unique addresses that end devices can communicate with each other. However, they work in the different network layers and perform their own duties.
MAC address is a hardware address that works at the Media Access Control (MAC) Sublayer of Data Link Layer (DDL), which is at the second position, so media access control address is also called layer 2 address. It is pre-assigned by manufacturers during production and can't be changed or reused. There won't be two NICs with the same MAC number.
IP address is a software address that operates at the network layer, which locates at the third position, hence the IP address is also known as the layer 3 address. It is assigned by a network manager based on requirements. If a device with a unique IP address is removed from the network, the network manager can reuse the IP number to address a new device connected in.
You are an employee named Elijah. your company assigns you a job number of 10345. On this year's annual anniversary, you win a prize for an iPhone 13. When you're going to pick up the prize, the administration staff confirms your name and also checks your job number. You may think it is redundant, but it actually works. Because your name may be reused, but the job number is unique.
MAC vs IP address relation is similar to the above scenario. When the data packet arrives on the LAN, it can be directly sent to the corresponding IP address host, so why ask for the MAC address of the IP host?
Here is a case example: If host 1 (IP address 192.168.1.1) wants to send messages to host 2 (IP address 192.168.1.2), here are two scenarios.
1. H1 and H2 are in the same network.
• H1 will broadcast: what's the MAC address of the node with the IP address 192.168.1.2?
• The corresponding host 2 with the IP address answers: my MAC address is 0000.0a1f.21a2.
• Then H1 communicates with H2 directly.
2. H1 and H2 are in two different networks, we should use gateway routers for forwarding traffic.
• H1 knows that H2 is in another network, so it accesses the physical address of R1 through ARP protocol. It is fa16.3e3f.fd3c.
• H1 then sends an IP packet to fa16.3e3f.fd3c of R1. The IP packet consists of a source IP address of H1 (192.168.1.1), a destination IP address of H2 (192.168.2.2), a source MAC address of H1 (fa16.3e87.9c2a), a destination MAC address of R1 (fa16.3e3f.fd3c), and the message data.
• When the package frame arrives at R1, R1 gets that the target IP address is 192.168.2.2.
• Since R1 stores the prefix of the network where H2 is located, it knows that it should forward the package to the hop IP address (192.168.12.2) of R2. R1 gets the MAC number of R2 is fa16.3e01.0c98 through ARP.
• R1 then sends a packet to the fa16.3e01.0c98 of R2. The IP packet consists of a source IP address of H1 (192.168.1.1), a destination IP address of H2 (192.168.2.2), a source MAC address of R1 (fa16.3e3f.fd3c), a destination MAC address of R2 (fa16.3e01.0c98), and the message data.
• R2 will go through a similar process as above, finally, the packet frame is succeded to forwarded to H2.
Now that you must have got the point:
When a data frame is sent from the starting address to the destination address, the data frame often needs to pass through multiple nodes to arrive. The source device does not know the hardware address of the destination device, but all nodes can access its adjacent node's MAC ID. It is the MAC address that enables actual communication.
IP address is responsible to deliver the data frame from the premier source device to the final destination device. However, the MAC address plays a bridge role to get data frames from one node to the other.
How Does a Switch Learn MAC Addresses?
As an intelligent bridge between host devices among LAN, the network switch helps send data to the addressed device with the MAC address. To present how switch MAC address works, here is an example.
There are four computers connected to a network switch. A wants to communicate with C, let's see what will happen:
First, A will check the MAC ID of C with the ARP protocol broadcast and send a data packet with the destination MAC address of C.
Once the packet is forwarded to the switch, the switch will check the MAC ID in its MAC address table. It learns the destination MAC address is located at the port linked with C. Then switch will only send a message out of the port connected to C. Thus it reduces the number of broadcasts.
B and D can simultaneously communicate no need to wait until the communication ends between A and C or other stations' transmitting (Carrier-sense multiple access with collision detection, CSMA/CD). Hence the utilization of switch improves the utilization efficiency of the network.
Benefits of Switches over Network Bridges, Router or Hubs
• Reduce broadcasts and improve the utilization efficiency of the network
• Enable redundant links for multicasts without network congestion
• Improve data security
• Makes multiple speed connections possible in one compact device
• In-built smart chips enable making decisions in hardware and high-performance
• Much higher forwarding frames in Ethernet
How to Find Switch MAC Address Table?
After knowing the working principle of the switch MAC address, one may ask: how to show MAC address tablet on Cisco switch? Here is a brief guide for your reference.
• Use show interface command to see switch interface MAC addresses
• Use show spanning-tree or show version command to see the Base Ethernet MAC address Bridge ID that is used in STP
• Use show mac-address-table command to see all MAC physical addresses that the switch has learned
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