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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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
87 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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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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1answer
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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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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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2answers
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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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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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3answers
9k views

Does Switch need its own MAC address?

I saw a post say Switch do not need its MAC address, unless it's an administrable Switch for managing. but I found the spanning-tree protocol need a MAC address of Switch to form STP Root Bridge ID. ...
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2answers
54 views

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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54 views

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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4answers
184 views

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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3answers
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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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MAC Address cloning. Why and when is it required?

REF: https://superuser.com/questions/932293/motorola-sbg6580-cable-modem-into-bridge-mode-on-bright-house-networks-does-not Question being, with cable based connections where your incoming cable can ...
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1answer
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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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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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4answers
136 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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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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1answer
103 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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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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1answer
51 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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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
95 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
63 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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4answers
2k views

How to detect the presence of a known MAC address on the .local ? (and get IP)

I would like to make a presence detection application which would be able to detect when a known device connects to the local Wifi network. So basically I would know the MAC address of the device, but ...
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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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527 views

Distributed Trunking Inconsistent MAC table

I've recently faced a problem in an HPE Distributed-Trunking Switch-to-Switch Square-Topology. Image 1 (shows the essential part of the architecture that consists of 4 switches working in pairs, ...
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2answers
39 views

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
1k views

Do typical Ethernet switches have timeout for MAC table entries?

Ethernet switches have a learning process through which they gradually begin to understand the network topology -- which MAC address is behind which port. When seeing a port to send a frame with a ...
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1answer
34 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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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
57 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
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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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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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Private IP vs MAC

What I know is that when we connect to another IP, our Public IP gets shared to the outside world, and when they address us they use our Public IP (gateway), and then the gateway directs the ...
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4answers
7k 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? ...
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2answers
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Why does a switch have different MAC addresses?

I am working with Cisco Nexus 3000 switch. I was under the assumption that a switch will always have a single MAC address but when I ran the following command, it displayed two different MAC addresses ...
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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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2answers
170 views

Basic understanding of network operation

Assume two stations, A and B, are connected by two intermediate routers. A----R1-----R2----B Now, when A sends a packet to B, then the OSI model will come into the picture. Like, A's TCP layer will ...
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2answers
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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2answers
152 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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2answers
2k views

Strange router's MAC address from ICMP Echo Reply?

Using Wireshark to capture ICMP packets (Windows) using ping to google.com, I can see the source-MACAddr of the ICMP Echo replies is not the same as the MAC address of my direct router (which is the ...
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1answer
314 views

Juniper EX4300 / MAC limiting SNMP trap

I have the following device and configuration: Model: ex4300-32f Junos: 17.3R3-S3.3 show configuration groups GLOBAL-SNMP { snmp { client-list MANAGERS { 10.8.9.0/28; } community TEST-COMMUNITY ...
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Endpoint MAC address change detection [closed]

A question regarding a host behavior when gateway mac address has changed (although it deals with Windows, I think it's the best forum). Assuming a windows host sending trafic to a destination IP, ...
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3answers
65k 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 ...
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1answer
89 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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3answers
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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2answers
177 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
913 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
54 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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