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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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5answers
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Why does ipv6 specify 128 bit address, when there are only 48 bits in MAC addresses?

So, I'm reading for a networking exam, and I'm just wondering if I have missed something basic. Is there a need for more ip addresses than MAC addresses, and how would a node with one network adapter ...
32
votes
8answers
7k 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?
24
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9answers
64k views

Reason for both a MAC and an IP address

If my computer has an IP address,why does it need a MAC address?
23
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1answer
110k 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: ...
20
votes
3answers
52k views

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 ...
16
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3answers
6k 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?
15
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4answers
5k 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 ...
14
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6answers
21k 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 ...
13
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3answers
15k views

Will duplicated MAC address give problems, if in different VLANs?

A small company has 2 Cisco Catalyst 3550, with 24 ports each, connecting their equipaments. After some trouble, we found that two NICs had the same MAC address. After the initial reaction of blaming ...
11
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3answers
11k views

Find MAC address of a remote computer using IP

Is there a way to find out a computer's MAC address if we know its IP address, assuming this computer is outside our LAN? I know we can easily get the physical address of a computer in our LAN using ...
11
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6answers
185k 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?
11
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2answers
11k views

Does the source MAC address of a frame change when it passes through several switches?

If PC1 sends an Ethernet frame to Switch1 which forwards the frame to Switch2 which in turn forwards the frame to PC2, does any decapsulation happen that changes the source MAC address?
10
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4answers
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Raw-Ethernet Frames

Recently I was puzzled by the following articles about Raw-Ethernet frames: RAW ethernet vs. UDP Message Passing Using Raw Ethernet Frames Briefly, both of them discusses that it is possible to ...
10
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2answers
12k views

Do Bluetooth Devices have MAC address with the same specification as the MAC addresses of the Ethernet and Wi-Fi Network cards?

I recently found out that ZigBee devices have MAC addresses. ZigBee is more related to Bluetooth from what I know rather than Ethernet or Wi-Fi. Do Bluetooth devices such as phones, headphones, ...
9
votes
3answers
31k 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 ...
9
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4answers
3k views

What use are MAC addresses? [duplicate]

I know that MAC addresses are used in networks for several things, e.g. static fixed IP addresses assigned by DHCP servers or for Wireless access points. But why is it necessary in the Internet? Let'...
9
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3answers
1k views

ipv6 addressing /127 vs eui-64

Best practice is to use a manual /127 address for point to point addressing described here RFC2373 for EUI-64 ERFC 2373 dictates the conversion process, which has two steps. The first is to convert ...
9
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3answers
10k 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?
9
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2answers
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. ...
9
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4answers
51k views

How to find a list of devices connected to my network (IP's and MACs)

I am trying to get a list of the devices that are connected to my Cisco (Catalyst 2960) switch. Preferably through SNMP. Here is what I've already done: I was able to retrieve the ARP table from the ...
9
votes
2answers
4k views

How to infer 2960S switch base ethernet MAC Address

Cisco switches seem to allocate unique MAC address for each interface they have, this includes ports and vlan interfaces. These unique MAC are derived from a "Base ethernet MAC Address", which can ...
8
votes
1answer
10k 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://...
8
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3answers
3k 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 ...
7
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4answers
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Does every host on the LAN share the same ARP table, or do hosts keep them individually?

I'm just learning about ARP. I'm a little bit confused. My confusion is better explained in a scenario. Host A is communicating with Host B. Host A knows Host B's IP address, but not it's MAC address....
7
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3answers
23k views

How can there be more than one MAC address on single switch port?

I am learning for the ICND1 exam through CBTNuggets video courses. In one of their videos they used a command, switchport port-security maximum This is what the cisco help says about it, To set the ...
7
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3answers
14k views

How does a switch know where to route packet, when there is another switch in front of the destination?

I am just wondering how a switch does know how to route packets to destinations "hidden" behind another switch. In my understanding a switch has a table that maps each of its hardware ports to exactly ...
7
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3answers
754 views

Does a switch always get a MAC address from a PC?

I was wondering if there is a possibility that a switch won't get the needed MAC address to it's CAM. For example, if the used protocol is UDP, where the sender doesn't need an answer back from the ...
7
votes
1answer
5k views

Is it possible to use single MAC address for multiple IPv4 addresses?

Topology: modem with router and Ethernet LAN bridge <---> server having one NIC. Server network interface: It is capable of handling more than one IPv4 address. All addresses are within the same ...
7
votes
2answers
1k views

Won't GLBP confuse a switch's mac address-table?

Say for example two routers (R1 and R2) are connected to the same switch (SW1) and both routers have Gateway Load Balancing Protocol (GLBP) correctly configured as the First-Hop Redundancy Protocol (...
7
votes
2answers
8k views

Why don't we use MAC address instead of IP for having “Internet” or doing communication? [duplicate]

We know MAC address is unique in each devices.So why can't we just send/receive data using MAC address only?
7
votes
1answer
1k views

HP Procurve 3500 with K.14 - strange MAC search issue

I have strange issue with HP ProCurve J8692A 3500yl-24G. If I display MACs on port I see it: 3500(config)# sh mac 10 | inc 5cf3fc-a53456 5cf3fc-a53456 But if I try to find where is this MAC then I ...
7
votes
1answer
3k views

Position of source and destination IP in an IP packet

In an Ethernet frame header, the destination MAC (DMAC) is placed before the source MAC for obvious reasons (stations accept based on DMAC). But why is not the same thing maintained for destination IP ...
6
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2answers
2k views

SVI as a DHCP client

Can a Cisco switch be configured to have a management interface (or SVI, or VLAN interface) become a DHCP client, therefore obtaining its own IP address on the respective network? This is out of ...
6
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2answers
178 views

How to display entire MAC address table on HP switches

I want to display the whole MAC address table without needing to press 'space' for the next page, so that if there are 50 entries in the table I'd be able to view them with a single command. I'm ...
6
votes
2answers
399 views

How to connect a special device in a network

I have a question which is puzzling me. I have a couple of custom electronic devices (are identical, one is a master and the other is a slave) which implement only up to level 2 of the ISO/OSI layer, ...
6
votes
2answers
594 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 ...
6
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4answers
8k views

Switch Lookup Table

I was just reading a book called HeadFirst Networking and I'm a bit confused about something. I am attaching an image from the book. The page says that the direction of the frames as maintained in the ...
6
votes
3answers
160 views

Lab: I need to determine information about a device on a specific port of a Cisco multilayer switch

I have a Cisco Catalyst that has a port that is up up, and the device does not show in the ARP table. The MAC address-table shows a MAC address for the port. What can I do from that switch to find out ...
6
votes
2answers
2k views

Cisco IOS: How to view MAC addresses on an Ethernet pseudowire

With two Cisco ME3600 (or similar MPLS & VPLS capable devices) running recent code [15.3(3)S], is it possible to show the MAC addresses passing over a standard MPLS encapsulated xconnect? In the ...
6
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3answers
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Using SNMP retrieve MAC addresses of directly connected machines to a switch

I want to get MAC address of machines directly connected to a switch using SNMP. I am querying dot1qTpFdbPort for this. But this returns all the MAC addresses learned by switch which includes machines ...
5
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3answers
3k 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 ...
5
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3answers
3k views

Do routers change MAC address of packets when forwarding

Lets say host A wants to send a packet to host B through R1(interface 1 then 2) and R2 (interface 3), so my questions is: When the packet is forwarded inside R1 (from interface 1 to interface 2), ...
5
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3answers
1k views

Why do we use VLAN?

According to my understanding, the network switch will look out for the specific MAC address and then it will forward the frame so basically it doesn't broadcast the frames then why do we make VLANs? ...
5
votes
3answers
985 views

Need help understanding how packets travel across the internet

I've been learning about networks recently at a new job, and I did a presentation on what I've learnt so far. When I was describing the relationship between the datalink and network layer, I mentioned ...
5
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2answers
8k 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 ...
5
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3answers
12k views

What to use as ARP request Target Hardware Address?

When sending ARP request, what must be filled in the target hardware address (THA)? This technet blog post says it is to be filled with zeros (0.0.0.0) -although doesn't look like a MAC address!, and ...
5
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2answers
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How ARP works in case of Virtual machine?

As far as my understading goes MAC address is used to recognize a computer node in a LAN where as internet communications happen over IPv4 address. When a request comes from the internet to the ...
5
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2answers
371 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 ...
5
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3answers
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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 ...
5
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1answer
3k views

What is the difference between ipNetToMediaPhysAddress and dot1qTpFdbPort?

I see the object description of ipNetToMediaPhysAddress from ipNetToMediaTable as the "The media-dependent `physical' address". Putting it simple, does it mean it returns the MAC addresses of all the ...