Questions tagged [mac-address]

For questions about Media Access Control (MAC) address which is used as the OSI layer-2 address for many OSI layer-2 protocols.

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How does a switch learn a switch table?

Say the switch table is empty. If computer A sends a frame destined to computer B, the switch will broadcast asking who has the mac address of B. What if C suddenly sends a frame to A? What is the ...
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  • 825
33 votes
8 answers
9k views

How can I stop an intruder plugging into an Ethernet wall socket getting access to the network?

Is MAC address filtering the most suitable option to prevent someone connecting their own device to the network by plugging into Ethernet wall sockets? What if they unplug a device and clone its MAC?
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20 votes
4 answers
15k views

Why is the CAM table in a switch called CAM table and not MAC table even though it holds MAC addresses?

I know the CAM table in a switch holds MAC addresses and the ports that are associated with the respective MAC addresses. There are no such thing as CAM addresses from my knowledge, so why is it ...
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11 votes
3 answers
7k views

Why do we need MAC Address if we can uniquely identify each machine with an IP Address

I learnt that in ARP Protocol, to send a packet from one machine to another machine we need to know the MAC Address of the destination machine but since the destination has already been assigned a ...
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9 votes
3 answers
5k views

Why do LANs use MAC addressing instead of IP addressing?

Why do LANs use MAC addressing instead of IP addressing? In other words, why can't a network just assign an IP address to a local area network device and send the data to that, instead of the MAC ...
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  • 377
52 votes
10 answers
95k views

Reason for both a MAC and an IP address

If my computer has an IP address,why does it need a MAC address?
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9 votes
3 answers
6k views

How are MAC/IP addresses used in routing

I have to teach my sixth form about MAC Addresses and IP Addresses in a few weeks time and there are some areas I am unclear on which I am hoping some of you will be able to clarify for me. I have ...
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14 votes
3 answers
49k views

How does a switch learn a MAC address not in its lookup table?

I have a relatively dumb question. Suppose the Switch just started, and it received a frame that contains a destination MAC address for a network device not in its MAC addresses table. What happens ...
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10 votes
3 answers
11k views

Why don't switches rewrite mac-addresses?

Is there any particular reason why Ethernet switches don't change the MAC address of a packet? Is it for end host identification using the MAC address, or anything else?
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  • 1,511
18 votes
6 answers
33k views

How are IP addresses mapped to MAC addresses?

I've been reading about the differences between MAC and IP addresses, and why we need both of them. To summarize, MAC addresses are physical unchangeable unique IDs for every single device while IP ...
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5 votes
2 answers
5k views

Does a switch MAC address table sync across all switches in the same VLAN?

Ok, I have read up about this 16K limit for the MAC address table, or better known as the CAM table, on certain switches. Lets say I have 14 different edge switches with that 16K limit, and I have ...
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  • 205
0 votes
2 answers
3k views

Confusions regarding byte and bit ordering of Ethernet Frame

I understand the concept of Endianess regarding numbers because there the bit significance is well defined. But when applied to things like Ethernet frame or Mac address, things are so clear to me, ...
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  • 103
5 votes
3 answers
9k views

How to trace a MAC address on a switched LAN?

How to trace a MAC address on a switched LAN? I want to be able to find out a switch port's MAC address. No device uses IP, therefore no address resolution and no SNMP. No device runs CDP, therefore ...
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1 vote
2 answers
2k views

How to make virtual devices on GNS3 be able to ping the physical host

I have had this problem already and figured out its reason. Basically the problem is that the virtual devices on GNS3 cannot ping the physical host and also the physical host cannot ping the virtual ...
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13 votes
6 answers
328k views

Finding Non-Cisco End Device IP Addresses Connected to Cisco Switch

I have Cisco catalyst switch, with many VLANs and address ranges. How do I find IP addresses connected to the switch that are not Cisco devices?
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  • 812
9 votes
1 answer
20k views

What are EUI-48 and EUI-64?

What are EUI-48 and EUI-64 addresses formed and used? Give me examples. What are MA-L, MA-S and MA-M assignments? I have read https://standards.ieee.org/develop/regauth/tut/eui48.pdf and https://...
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8 votes
6 answers
2k views

How Does A Layer 2 Switch Differentiate Between Different Networks?

I know that different IP-based networks can be connected to the same layer-2 switch. and I know each network's nodes can communicate just fine, however, no normal traffic can occur between two nodes ...
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  • 183
38 votes
2 answers
157k views

TCPDump - Filter by MAC Address

I would like to display all traffic for or from a specific MAC address. For that I tried sudo tcpdump host aa:bb:cc:11:22:33 It does not work and returns me an error tcpdump: pktap_filter_packet: ...
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  • 693
8 votes
2 answers
12k views

Why each and every single port on Layer 2 switches need to have it's own MAC address?

A switch doesn't alter the frame, and source/destination mac addresses remain how sending host specified them,so let me say it again Layer 2 Switching never changes the frames means no changes in MAC ...
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  • 415
4 votes
2 answers
14k views

What does a switch do when the destination MAC address is unknown?

Say I just connected my computer to the internet through a home/office LAN network. I then proceed to ping google.com. Of course, the DNS converts google.com to the destination IP address, but how is ...
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9 votes
2 answers
2k views

Differences and functions of type codes 0800 and 0806

What are the primary differences and functions (or applications) of type codes 0800 and 0806? Through my own research, I found the 0800 was related to the 0800 to the IP/Layer 3 of the OSI model. ...
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  • 303
5 votes
2 answers
196 views

does MAC filtering provide security against MAC spoofing in wired networks?

i have googled about mac address spoofing.All I know is that MAC filtering is not much of a protection in wireless network.And in wired network it only works for routers that support MAC Filtering.Is ...
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5 votes
2 answers
2k views

Did the LSB-first method of transmitting the canonical MAC address in Standard Ethernet have any specific advantages?

When MAC addresses are sent out they are sent such that the Group Address Indicator is the first bit of the Ethernet frame but when stored in memory this forms the LSB of the leftmost byte of the MAC ...
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0 votes
3 answers
1k views

How do 2 PCs learn each other's IP addresses for ARP resolution? [closed]

So, if one PC will use another PC's IP address for ARP resolution, how does the PC sending the ARP Request even know which IP address to call for in the first place? What happens in a scenario where ...
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17 votes
3 answers
24k views

Can my MAC address be identified by a web site?

Can my MAC address be identified by a web site when I access the site? Does it make a difference if the site requires me to upload files?
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  • 273
7 votes
3 answers
2k views

IP Address vs MAC Address, how does that really work together illustration

My question is simple, i don't really know if I understand it so I'm asking. Why do we have both addresses, if we know the ip address of the target and source computer, why do we need some physical ...
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  • 91
5 votes
2 answers
744 views

Learn MAC addresses via replies to other hosts requests

I have a question regarding ARP: If host A wants to send a message to host B and the ARP table of host A does not contain a MAC address for host B then he sends an ARP request and host B replies with ...
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5 votes
1 answer
2k views

MAC address can be used to generate an IPv6 link local address

MAC address can be used to generate an IPv6 link local address. What is the process of using MAC address to derive an IPv6 address ? What are the problems that can be caused due to process of using ...
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4 votes
1 answer
5k views

What happens if two hosts with the same MAC address are in the same broadcast domain?

I am aware that situation, where duplicate MAC addresses appear in the same broadcast domain, should never happen. However, if such situation happens, then how will the network work? I think one ...
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  • 1,295
4 votes
2 answers
565 views

Learning of MAC addresses with cut-through switching?

I would like to ask, what part of frame is actually read in cut-through mode of switching? I understand that as soon as he read the destination MAC address it can forward. However, how will switch ...
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  • 386
4 votes
1 answer
243 views

How do we prevent loss of sensitive information from MAC spoofing?

While IP addresses are often dynamically assigned during runtime, hardware addresses (so called MAC addresses) are usually statically allotted when a network interface card is manufactured. What ...
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4 votes
3 answers
1k views

What is the point of ARP?

I'm a complete beginner at networking, but if I've understood this correctly, the gist of ARP is: We want to use high level adresses to the highest degree possible but ultimately, we actually need ...
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4 votes
1 answer
2k views

Cisco Catalyst 2960 X MAC access list

I am using a MAC access list on this switch, so I go about it by first creating the MAC access list: #conf t #mac access-list extended aclname # permit host XXXX.XXXX.XXXX any Then, I tie this list ...
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  • 85
3 votes
2 answers
223 views

Client timeout for Cisco IOS Static DHCP Pool

I'm not a network admin, but I have an old Cisco Catalyst 3560 for my network. I've successfully set up a DHCP Pool: ip dhcp pool 192.168.0.0 network 192.168.0.0 255.255.255.0 default-router 192....
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  • 133
3 votes
2 answers
645 views

Is an IP address necessary for a gateway?

When a IP sends something to another host outside the same subnet, it constructs a packet (L3) with the target IP being the IP of the target host, but the frame (L2) has the destination address = ...
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  • 205
3 votes
2 answers
407 views

Why do we allow Mac-Address to be changed by software?

In CISCO routers, they provide a provision to change the MAC-Address. My question is MAC-Address is supposed to be a burned-in address i.e. a permanent address. If we allow the mac-address to be ...
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  • 325
3 votes
2 answers
741 views

Mobile cellular Networks (GSM, LTE, 5G, ...) and MAC addresses

We've been provided with a new firmware for our telematics units, which connects to the Internet via a VPN provided by a mobile carrier; since this new firmware release, we've noticed that each and ...
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  • 133
3 votes
1 answer
607 views

MAC Spoofing and EUI-64

I have two questions that both assume an attacker who has my MAC address: Suppose an attacker connects to the Internet before me, spoofing my MAC. I then connect and tell people to connect to my EUI-...
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2 votes
2 answers
497 views

Does host really resolve end Host IP or Gateway?

Assume I have following connections: [HostA] - - - - R1---- Internet - - - - R2---- [HostB] Now, I want to communicate from HostA to HostB, Does HostA really resolve the HostB IP address, or if it ...
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2 votes
2 answers
2k views

How to find the switch IP address based on MAC address?

On PC, the extra network adapter is configured as static 192.168.2.1. A switch with DHCP enabled is connected to 192.168.2.1 and if I login using the console (RS232) I see that it has 169.254.x.x ...
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2 votes
2 answers
175 views

Spoofing the L2/L3 information and replication across L2

Could I have a server that spoof the same IP/MAC address of my server on the same L2 network that: 1 - does not do any conflict on the network. 2 - And on the same time when capturing packets on my ...
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1 vote
2 answers
502 views

How does a switchport learn a MAC address

I have a very basic question. How does a switch port learn a MAC address? In this scenario say a host is not trying to communicate with any one. It is just plugged in the switch port. Does the host ...
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  • 111
0 votes
1 answer
86 views

Network flooding without ff-ff-ff-ff-ff-ff (layer 2 broadcast) MAC address in destination? [closed]

It appears that a switch is sending the same traffic to all ports in a VLAN: In a Wireshark capture on host 192.168.0.10 with MAC aaaa.aaaa.aaaa I see packets with MAC destination bbbb.bbbb.bbbb and ...
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0 votes
3 answers
157 views

Propagating Static MAC Addresses

I have a situation where I need to place a static MAC on a switch as the server in question does not generate any outbound traffic. This static MAC seems as if it will work for hosts on the same ...
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0 votes
1 answer
343 views

Why is default gateway in routers configuration usually set as an IP address?

I mean why not just: a MAC address? It should eliminate the need in ARP requests asking for gateway address. Also it should eliminate the need in changing IP addresses in settings when gateway IP is ...
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  • 111