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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What happens if the layer 2 destination MAC address mismatches?

I was wondering, what happens if I send a packet with layer 2 destination (say 1ebf) different that what will receive it, lets say a router (mac 22ff) recieves it. Will it drop the packet? Or ...
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3 votes
2 answers
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Show port on Cisco switch that mac address is being dropped on

We use ISE to handle port security on our switches. When I see that there is a mac address being dropped by the switch it doesnt show what interface this mac is patched into. #show mac address-table (#...
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Do the source MAC address and the destination MAC address change on each router? [duplicate]

I know that when a device sends a packet in a LAN, the packet source MAC address must be the MAC address of the device sending the packet, and the destination MAC address must be the MAC address of ...
3 votes
3 answers
120 views

Can you send data in LAN without an IP?

From What I know, IPs are used to communicate b/w two different networks say LAN1 and LAN2... and MACs are used to communicate within a LAN.. I think this because my instructor says that Hubs and ...
0 votes
0 answers
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Access point MAC addresses shows up in Floorplan deployment instead of the access point names

I have about 5 Aruba access points assigned to a site called storage that I have configured in the mobility conductor to have names based on the rooms they are placed in. When these are later on going ...
1 vote
1 answer
53 views

Does RSTP also maintain correct mac table entries?

I've got 4 switches connected in a circle and they all run RSTP. Lets assume the following: switch A (root bridge) ------- switch D | | | ...
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21 views

What is the difference between a private IP and a MAC address? [duplicate]

I am taking a course preparing me for the Network+ certification. I wanted to know what the purpose of a private IP is when a MAC address exists. From what I understand, the MAC address is used to ...
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1 answer
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What are the IP/MAC addresses of requests between 2 different subnets? [closed]

Assume that networks 172.15.10.0/24 and 172.15.11.0/24 are connected through a router with interfaces 172.15.10.254 (MAC3) and 172.15.11.253 (MAC4). If host A sends a packet through its network ...
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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1 vote
3 answers
132 views

Why switch uses Mac address during implementation of spanning tree protocol (STP)?

We know that layer2 switch doesn't use Mac address ,uses only certain port number to accept the frame. But I have been read on book as well as internet that uses Mac address to find spanning tree for ...
1 vote
0 answers
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MACsec encryption feature on Cisco NX-OSv 9000 Virtual Software?

https://www.cisco.com/c/en/us/td/docs/switches/datacenter/nexus9000/sw/7-x/nx-osv/configuration/guide/b_NX-OSv_9000/b_NX-OSv_chapter_01.html The above link only stated some examples of features which ...
3 votes
1 answer
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How are IP broadcasts handled at lower levels

When I use a broadcast IP address, for example 198.255.255.255, what will happen when it gets passed down to the link-layer which will then look for the corresponding MAC address in your ARP table. ...
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2 answers
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How PPPoE uses addressing to know destination Mac address?

Case.1 We know that when router connected via point to point(PPP) protocol then ARP isn't used to know the destination Mac address. Case.2 When two router connected via PPP as well as Ethernet which ...
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1 answer
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Understand router Ip address and Mac address, Switch Mac address

Scenario:1 Suppose external Router R1 has interface a connected with interface b of the site Router R2. And Router R1 using IP address 80.0.0.0/8 for a. Router R2 has 4 subnets 80.0.0.0/10, 80.64.0....
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2 answers
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using Cisco WIC-4ESW 4PORT ETHERNET WIC Card (L2 switching card) on a 1700 Cisco router, where the router stores the MAC address of connected devices?

Router is an L3 device, but some models (such as Cisco 1700 router), we can attach the WIC-4ESW which is L2 switching card. as per the offical Cisco datasheet: The WIC-4ESW interface card is a Layer 2 ...
3 votes
2 answers
824 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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-1 votes
2 answers
74 views

Multicast MAC using destination MACs

I am working on a routing algorithm which involves multicasts, my question is: Is there a possible way to convert a list of MAC addresses to a single multicast MAC address for configuration purposes? ...
5 votes
1 answer
2k views

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 ...
5 votes
1 answer
162 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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4 votes
1 answer
485 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?
0 votes
1 answer
181 views

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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3 answers
138 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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1 answer
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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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2 votes
1 answer
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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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2 answers
151 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, ...
0 votes
2 answers
64 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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1 vote
2 answers
59 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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3 votes
4 answers
228 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 ...
0 votes
2 answers
46 views

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 ...
0 votes
1 answer
151 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 ...
0 votes
4 answers
566 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 ...
0 votes
1 answer
249 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: ...
0 votes
1 answer
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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 ...
1 vote
2 answers
89 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 ...
1 vote
4 answers
343 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 ...
0 votes
1 answer
97 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 ...
0 votes
2 answers
59 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 ...
0 votes
1 answer
59 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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1 vote
2 answers
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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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1 answer
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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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1 vote
2 answers
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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 ...
1 vote
1 answer
93 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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1 vote
1 answer
149 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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1 vote
2 answers
398 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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2 votes
2 answers
1k 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 ...
0 votes
1 answer
91 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 ...
0 votes
1 answer
55 views

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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1 answer
455 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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