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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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Why are ARP entries on my computer missing when hosts leave the LAN? [on hold]

From my understanding, an ARP entry occurs when you communicate with a device on your LAN. This ARP entry resolves the I.P. address and caches it for your host the next time it needs to communicate ...
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2answers
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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 ...
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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....
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1answer
48 views

MAC Table vs ARP

I understand that for a switch to learn a MAC address, if host A wanted to send data to Host B the switch learns host A MAC and places it in the MAC table. If it doesn't know where the MAC (for Host B)...
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3answers
234 views

Switch and mac address table

I thought that a switch learnt the mac addresses by the computers sending out packets. However when I configured 2 switches, and 2 pc's, 1 pc connected to 1 switch, the other pc connected to the other ...
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3answers
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Is an IP address assigned only to something with a Mac address?

From https://en.wikipedia.org/wiki/IP_address An Internet Protocol address (IP address) is a numerical label assigned to each device connected to a computer network that uses the Internet Protocol ...
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1answer
58 views

Port security on a cisco switch - predefined source MAC address and maximum number of MAC addresses

With port security on a Cisco switch, if you configure 1 source MAC address, does that also set the maximum MAC addresses to only one?
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2answers
51 views

How does a router know the destination mac?

so if I send a packet from a host to another from the same network we know the mac address of both the source and destination. However if the receiver is in a remote network the destination mac ...
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2answers
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What is the bridging decision when getting ARP request?

Setup: Assume I have 3 VMs. VM1 VM2 and VM3. VM2 has two interfaces, say eth1 and eth3. eth1 is connected to VM1 physically and eth3 to VM3. I create a bridge on VM2 using brctl with eth1 and eth3. ...
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3answers
67 views

Is it possible to perform a Layer 2 (MAC address) traceroute?

I understand the difference between layer2 & layer3 and MAC & IP. I understand address resolution protocol, etc. But is there any way to do a traceroute that will show Layer 2 information? For ...
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2answers
72 views

Why we need ARP when each device has its own IP address?

I don't really understand Address Resolution Protocol (ARP). Why we need ARP when each device has its own IP address?
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1answer
27 views

locally vs universally administered MAC address? [duplicate]

Difference between locally and universally administered MAC address? What is the purpose of locally administered MAC address?
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If ARP uses broadcast, can I find out MAC-Address AND IP with it?

I have a peripheral device, connected via Ethernet to my Ubuntu. I would like to find out its IP, and untofetunately no it is not cached in my ARP table. ARP broadcasts the messages to every ...
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1answer
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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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2answers
32 views

LANs with no router,just a switch(or hub)

Can a LAN be implemented just with a switch? If so,how is the communication completed?just by MAC addresses? When sending a frame from the source to the destination,and inbetween there is a switch,...
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1answer
130 views

Cisco ARP cache rewrites?

I know that the Cisco's default ARP entry expiration is 240 minutes, however how does the ARP table mechanism work when a different MAC address is seen using the same IP? In other words, if I move ...
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1answer
70 views

Changing MAC Address

On learning about MAC addresses i came across U/L bit in the first octet. Further on i learned that MAC address could be spoofed. If U/L bit switches according to MAC address modification , how ...
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3answers
554 views

What is responsible for dropping Layer 2 frames that's not addressed to it?

It's my understanding that if a network interface card (NIC) receives a Layer 1 packet, it will extract the Layer 2 frame from it, checks its destination MAC address, and if it is not addressed to it (...
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1answer
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will wireless devices' MAC address be saved on layer 2 switch?

So I know that basically switches work like this (assuming 2 PCs are connected via Ethernet port) - the switch will store the mapping of the 2 PCs' MAC address and the switch ports in which they ...
4
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1answer
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What are the various standard and industry practice ways to express a 48-bit MAC address?

My team builds software that allows MAC Addresses as user input. These addresses are often copy and pasted from various platforms in a variety of formats. Wikipedia documents MAC Address Notational ...
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1answer
23 views

Global Unicast in IPv6 Neighbor Discovery

I have a very small pcap file in which Neighbor Discovery is performed for Global Unicast Addresses. That is, IPv6 addresses of both neighbors as I can see in Wireshark start from 2001:. Both IPv6 ...
6
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2answers
382 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, ...
4
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3answers
160 views

Is there any relation between MAC addresses of a dual band (2.4 and 5 GHz) router?

I have a use case where I need to determine whether two MAC addresses belong to the same router with dual band connection 2.4 GHz and 5 GHz. When I did some study, I found that the MAC address of ...
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2answers
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Reliable “Decentralized” approaches for MAC spoofing?

Among all techniques proposed to detect MAC spoofing, is there a reliable and decentralized approach such that we can detect this type of attack strongly? Some of proposed approaches are as follows: ...
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2answers
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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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1answer
55 views

What's the `CPU Interface` of Switch?

What's the CPU Interface of Switch? in the 2960-24TT Switch, there is a CPU Interface in it. Switch#show interfaces | begin CPU Hardware is CPU Interface, address is 0002.1669.5897 (bia 0002.1669....
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2answers
217 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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1answer
35 views

Is it a protocol of flooding to find the MAC address?

Is it a protocol of flooding to find the MAC address? As we know, if the switch can not find a MAC address, it will flooding to every switchport except the entry port to find the corresponding MAC ...
3
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1answer
317 views

Port Security Or 802.1X Authentication On Non-Server Network

I have a closed network of 3 switches and 40 computers. 35 of those computers (Windows 7 x64 Professional) need to be plugged into any of the 24 ports on 2 of the switches at any time depending on the ...
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3answers
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How did one go from IP to MAC in classful networks?

This is more of a question asked out of curiosity than for practical reasons, but it's bugging me, because it might point to a lack of understanding elsewhere. Back when classful IP addresses were ...
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3answers
669 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 ...
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3answers
222 views

Cisco Switch ports and MAC addresses

Good morning, How do I find out which port on a Cisco switch is connected to a particular MAC address? I recently took over Network Administrator position and trying to clean up and organize. Thank ...
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2answers
96 views

Why two hexadecimal digit can only stand 8 bits in MAC address?

This is one of my network adapter, the MAC address is: a0:99:9b:17:52:07: en0: flags=8863<UP,BROADCAST,SMART,RUNNING,SIMPLEX,MULTICAST> mtu 1500 ether a0:99:9b:17:52:07 inet6 fe80::c48:...
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3answers
189 views

Dynamically learned MAC address seems to never expire

I have a user getting error "No logon servers available" at login on a Windows machine. Topology is this: R1--SW1--IP phone--PC1 I cannot ping PC1 neither from its gateway R1 nor from SW1 (access ...
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3answers
2k 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), ...
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1answer
244 views

Finding the source MAC address in Router Advertisements [closed]

What is the source MAC address in the Router Advertisement packets received on the interface eth1? -i have ran tcpdump -i eth1 and tcpdump -n -i eth0 icmp6 -ifconfig eth1 and tried using the HWaddr ...
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1answer
315 views

Is there a way to “Pass through” a MAC address on a Cisco Switch?

We have two systems connected together, and the end system (system 2) relies on differentiating packets via MAC address from system 1 (it has two routes). For testing purposes, we want to put a ...
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2answers
68 views

Possibility of using Cisco “port security” in sensor networks?

Is it possible to use Cisco port security (to prevent a host changing its Mac address) in sensor networks? In a more general question, is Cisco port security platform independent? Meaning that it is ...
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1answer
66 views

Possibility of recognising a computer in the network that has changed its mac address?

Consider a computer with Mac address (physical address) A, joins a network, and then it changes its Mac address to B. So, the network is able to recognise such a computer?
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2answers
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Determine whether the MAC address is of a router or the destination computer?

In a given Ethernet frame containing the HTTP GET message can we tell apart whether the MAC address of the destination is of a router or end host? The link to ethernet-ethereal trace :: https://drive....
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2answers
59 views

Why don't switch MAC addresses conflict

Switches apparently have a base MAC and self-generate MAC value for each port from that base. If a company that makes both switches and processor boards builds a switch and assigns it MAC "N" and ...
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3answers
85 views

Why do we need an ethernet MAC address? [duplicate]

Don't think it's a duplicate. I've searched really many articles and couldn't find the satisfying answer. I understand : how ARP works MAC address is an unique address for each NIC IP is network ...
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1answer
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switch filter a frame

I was reading a text book, it says suppose a host A sends a frame with destination address DD-DD-DD-DD-DD-DD arrives at the switch on interface x. The switch indexes its table with the MAC address DD-...
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1answer
34 views

How does MAC spoofing happen? [closed]

I know how to change my MAC address, but I want to know how does this happen, or how the programs that do so work.
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1answer
238 views

Setting MAC source address to broadcast

How would a network behave if one were to set the source address of an Ethernet frame to the broadcast address FF:FF:FF:FF:FF:FF? Obviously, one would have to manually alter the relevant field in the ...
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2answers
84 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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2answers
55 views

Why router interface need IP addresses while IP is constant during the journey?

A beginner question, I've recently read in Cisco CCNA R&S 200-125 official cert guide that the packet leaves the PC with a destination IP of PC2 (the target) but with the MAC of PC2 in case of PC2 ...
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0answers
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Same mac addresses for all the IPs [closed]

So I'm on a public wifi network and I'm trying to do intrusive testing. The issue is that while doing arp scan all the IPs are returning the same mac addresse.
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2answers
112 views

How does a wireless repeater ascertain the destination MAC address of a wireless client?

While diving into the depths of wireless networks I have come across the different address fields in the MAC header of 802.11 network frames. A few thought experiments later I was confused about a ...
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5answers
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Is there a Layer 2 address advertising protocol?

I needed help in understanding if LLDP/CDP is the Layer 2 equivalent to RIP or say any Layer 3 route advertising protocol. If not,is there a protocol that advertises the MAC Address Tables among ...