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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Does an unmanaged switch deal with IP addresses at all

My belief is that an unmanaged plug-and-play layer 2 network switch only deals with MAC addresses. When computer A on a local network wants to communicate with computer B for example through the ...
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1answer
142 views

MAC collisions in Probe Requests

To find nearby routers, mobile devices send probe requests to coax the routers into sending probe responses. Since modern devices don't use their actual MAC address anymore but instead rely on MAC ...
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1answer
458 views

Can a radio share a MAC address with the ethernet interface of an access point?

I have a situation where I have found the BSSID to have a MAC address congruent to the MAC address of the ethernet interface. Is this possible? Does this happen with all access points?
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How do we identify an address as a valid MAC address

If 000.a83.b1c.08e is a valid MAC address then why is 123.123.123.123 not a valid address? Also if how do we identify its 32 bit long or 48 bit long
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Types of ARP messages [duplicate]

I have a little misunderstanding which message type the ARP protocol supports. From this link we can see that the ARP header consists of these fields: Hardware Type–It is 1 for Ethernet. Protocol ...
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3answers
91 views

Do hosts in the same LAN know their MAC addresses?

I am trying to learn about how ARP protocol works in LANs. So, here is the physical structure of my network: So, when I try to ping PC3 from PC1, I expected the first packet to timeout because PC1 at ...
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1answer
45 views

How to determine if a network cable is bad on a LAN under an unmanaged switch with no DHCP?

Is there anyway to detect this via automation and software? I know if I can get access to the MAC address table on the switch I can see if there's a missing MAC address. I don't know if this is ...
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14 views

lan with multiple ip [duplicate]

If imagine lan assigned ip from from this range (192.168.1.0/24) then can we assign another ip from same subnet mask? If no why?
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1answer
38 views

Can wifi clients in same subnet talk to each other without a WAP?

I understand that a L2 device like WAP is needed to forward packets from one client to another within the same network (based on MAC mostly like in 802.11) However my question is, if there is no WAP ...
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108 views

Is knowing MAC needed for talking to another device in same wifi network?

I have heard about ARP protocol for learning MAC address of other devices in a LAN for communicating with each other. However, I am bit confused about how it works in a typical infrastructure mode, ...
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Client's ARP requests affect whether Cisco C897VA receives packages or not

So I have bought used ISR C897VA with an issue: when vlan1 is pinged from windows there are quite a lot of "Request timed out"s. Config-register 0x2142 has been done, as well as resetting ...
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2answers
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Can Vendor User Mac Address of Another?

I heard that each vendor is given a specific start in the Mac Address to use. What's the problem of me creating a company and using the start of Mac Address given to google or Cisco? how is this ...
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Question about ARP requests

When a device tries to associate an IP address with a MAC address for a given device, it sends ARP requests to all devices connected to the same network. If I understand correctly, the searching ...
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2answers
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How to tell if a device on the network is an access point?

Let's say we have a network with multiple access points. The command arp -a can be used to list the IP addresses and physical addresses of the devices that are on the same network. Now, is there a way ...
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1answer
31 views

How does NAT modify the headers correctly?

How does the process of replacing the incoming message (say from stackexchange) to the router, and modifying the header with my PC IP happen? How does the router know which IP to insert there? Is ...
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Can two hosts with different subnets connected with a switch talk if they know each other's MAC address? [duplicate]

EDIT: There is a seemingly similar question already, but it doesn't explore what happens if you don't need to do an ARP request at all, which is what seems to be hindering the communication there. The ...
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4answers
196 views

What if a host makes an ARP request for an IP outside its subnet?

I have read other similar question on the forum and none have completely answered my question. But to understand my confusion, you would need to know what else I'm confused about. Is ARP a layer-2 or ...
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1answer
116 views

Unknown cause of disappearing CAM table entry and unicast flooding

Posting this in response to the closed question: Network flooding without ff-ff-ff-ff-ff-ff (layer 2 broadcast) MAC address in destination? I have a network that is experiencing the following problem: ...
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1answer
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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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2answers
63 views

Under what circumstances is the ARP table updated?

Lets say we have 3 devices in the same shared medium : A, B and C. A wants to send a message to B, so before, it sends an ARP request as a broadcast message. When B receives it, it will update its ARP ...
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4answers
104 views

Do layer 2 protocols allow hosts to communicate without being on a network?

Please go easy on me as I'm just a noob in the networking space. As far as I have learnt, layer 2 protocols use MAC addresses for communication, which doesn't really depend on what network you're in ...
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1answer
64 views

can two devices communicate without physical layer?

can 2 device communicate with each other without data going to physical layer? for example we just use protocol of data link layer that use MAC address , but transferring this frame data between 2 ...
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PPP vs PPPOE vs Ethernet frame [duplicate]

PPP is a protocol that encapsulate data for point to point communication between 2 device that know mac address of each other ( I say they are in a scope that can see each other) why we need PPPOE and ...
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Is there a layer 2 protocol that can be used to send arbitrary data?

I would like to design several devices that receive simple commands from a single controller device all residing on the same layer 2 switch. Is there a protocol that allows me to do this without ...
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1answer
36 views

Do unicast frames get sent to all switches associated with the target VLAN?

If a network topology has a VLAN which spans multiple switches, what happens if a frame is sent to a MAC address that is connected to the source device's "home" switch? By that I mean if a ...
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2answers
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Basic conceptual questions about network interfaces

I have some basic questions as I am trying to understand the concept of network interfaces a bit better. Is network interface same as network interface card (NIC)? If not, what's the difference. What ...
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1answer
28 views

issue regarding broadcast mac address

I read a line saying {Routes do not forward packets coming from one interface having broadcast mac address (FF:FF:FF:FF:FF:FF)} what is meant by one interface in that line? if router cannot broadcast ...
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2answers
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What is Mac Addressing in terms of Networking

I want to ask what does the term "Mac Addressing " mean ? I know what is a Mac address ,but when we say for example that "one of the functions of Network Interface Card (NIC) is MAC ...
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1answer
63 views

Mac Instability in STP after topology change!

So I'm learning about STP and I recently been taught that when the topology is changed due to direct or indirect Link failure a Mac Instability could occur, So I was wondering, If the blocked port is ...
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1answer
95 views

How does router know MAC addresses of computers that are connected to a separate switch? [duplicate]

i am a newbie but i need to understand this ARP thing. In my company we have a router that has 3 switches connected to it. On the switches there are more than 100 hosts. I know that switch learns and ...
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2answers
215 views

How does the ARP table know to update if two hosts flop IP addreses?

When hosts on the same local network communicate, they manage their own ARP tables which translate between IP addresses and MAC addresses. Thus when computer A needs to send data to IP address ...
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2answers
988 views

MAC address and unicast, multicast and broadcast

I'm very new to computer networking and I'm trying to figure out this dilemma about the Unicast, Multicast and Broadcast transmissions. I was told that MAC address are unique for each device and they ...
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1answer
59 views

What if receiver changes its IP address during the transmission process?

Suppose I am sending data to a laptop with IP address say x but before data could reach its destination the laptop is moved to another network and now its IP address becomes Y. Will the receiver still ...
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BPDU Header System ID Extension

Previously network switches was using the 8 byte field Bridge Priority to identify a root on the network.When networks grows and becomes complex vlan creation comes into play the 2 bytes Bridge ...
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1answer
316 views

Sending a gratuitous ARP on an interval - Cisco

In response to my question Propagating Static MAC Addresses , I realize I can not avoid the unknown unicast problem. Essentially I have hosts that forward their traffic via an L2 frame to a ...
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3answers
117 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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1answer
48 views

Huawei switch mac address sticky (model S5720) persistence after power cycle

Suppose I configure the commands "port-security enable, port-security mac-address sticky" in a Huawei switch port, then an endpoint device is connected on the switch port, and a MAC address ...
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2answers
296 views

Are all packets addressed with the MAC address of the router as they leave the machine?

In the Comptia Network+ All in One, it is said that most home routers have a switch built into them. It is also said that the first thing the router does is strip off any layer two information present ...
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1answer
179 views

Unicast and Multicast MAC address convention

I need help in understanding how Unicast and Multicast MAC address is differentiated as explained in wiki. According to what I understood, when the least significant bit is set as 0 in the first octet ...
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2answers
66 views

Can a host from different subnet bypass the network mask validation of destination host and communicate on layer 2?

I am aware that a host will always check the subnet of the destination node before the transmission in order known if it has to send it to the gatewey for different subnet. However, would it be ...
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3answers
121 views

Forwarding and routing table for host [duplicate]

I'm new to computer networking and from what I've studied, I've understood that Forwarding tables map MAC addresses to ports. So they are used by switches. Routing tables map IP to IP ..they define ...
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2answers
390 views

Why do WiFi bridges replace the source MAC Address with their own?

Ive read quite a bit about the issues i currently have with my Aruba WiFi Bridge 501 and the failure of DHCP going through, and as far as i can tell the issue is that the bridge replaces the MAC of ...
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1answer
44 views

Unknown device mac address listed in switch table on start out

After playing a little bit with a topology randomly created in packet tracer, I figured out that the switch (Switch0) stores a unknown device mac address on start out, wich I think that it belongs to ...
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1answer
68 views

Filter Packet PPPoE Discovery

i have a sw nexus i have a router BGN with vlan 50 is going to sw then mode access to Client 1 and Client 2 BNG ==== SW1 == PORT1 =Client 1 (Mode access vlan 50) PORT2 =Client 2 (...
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1answer
331 views

Multiple mac adrress on one cisco switch interface

How can i config Multiple mac address on one cisco switch interface? (I have 3 laptops and i connect only one laptop every time(I switch between them), and i want to config only one interface with the ...
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0answers
904 views

How to block unknown MAC addresses in OpnSense

I'm dealing with an OPNSense router, at the moment I already configured the DHCP server to provide IPv4 addresses only to a legitimate list of fixed MAC addresses and I want to block every unknown MAC,...
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1answer
26 views

decoupling of network and link layer addresses

can you pls help me understand what the instructor is trying to convey in the following slide. from what I understand:- network address and link address are independent in the protocol layers but ...
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2answers
984 views

How do hosts subscribe to multicast addresses?

So I am having a hard time finding materials online that explains how multicast address are set. I understand what unicast is: Basically one to one communication. In this scenario, an address ...
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2answers
59 views

Will the switch itself interfaces store in the MAC address table?

I have a topology like this: the port and mac address map: Mac address Interface ----------- --------- aa:aa:aa:aa:aa:aa - pc1 bb:bb:bb:bb:bb:bb - pc2 cc:cc:cc:cc:cc:cc - sw1_ac dd:...
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2answers
1k views

Does a PC have a MAC address table?

I have a network topology like this: We know switch has MAC address table, but does the PC have MAC address table? I know PC have ARP table in Windows I can use arp -a display all the arp information ...

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