Questions tagged [mac]

Not to be confused with mac-address tag, Media Access Control is a sublayer of the OSI data link layer that provides addressing and channel access control mechanisms. It resides between the LLC sublayer and the physical layer.

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Mechanism/purpose of the NAV and its relation to the exposed node problem in 802.11

802.11 uses csma/ca as the mac protocol. Every station senses the medium, if something is being sent, then they will set their NAV to the duration ID from the packet being sent weather RTS, CTS, DATA, ...
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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 ...
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How FDB (Filtering Database) is filled out

I would like to understand what is used as a VLAN column in the FDB. For ACCESS port it is PVID if frame untagged or frame VID if frame is tagged, for TRUNK it is allowed VLANs? We can represent the ...
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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 ...
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Does MAC replace CSMA/CD in Ethernet?

We now that in old days Ethernet use CSMA/CD for collision domain. However, with the advent of Switches now MAC addresses are used to identify the source and destination machine. But still when I read ...
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Slotted ALOHA probability and efficiency

Given: There are two active nodes, A and B, in a slotted ALOHA network. Node A transmit in each slot with probability a while Node B transmit with probability b. The first slot is numbered Slot 1, the ...
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Duplicate IP in one LAN

I have a small LAN. there are: One linux PC with IP x.x.x.10 an unmanaged switch two different devices that share the same IP (x.x.x.1) (lets call them device 1 and device 2). The idea is to power ...
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Cisco MAC ACL loop holes

I know this is not a new topic but need to clarify a couple things. I have a typical office with hosts connected to a Cisco 3560-X in same VLAN. My goal is to prevent unauthorised hosts ever accessing ...
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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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IP_PHONE_POWER_ADAPTER IN CISCO PACKET TRACER FOR MAC

I'm using Cisco Packet Tracer v8.0.0 for Mac, and I'm having trouble connecting the ip_phone_power_adapter module of the "7960 ip phone" device. According to several tutorials, you just drag ...
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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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How do switches learn the neighbour MAC address? [duplicate]

According to the CCNA Official Guide a switch learns the new MAC address by checking the source MAC address of a new frame. Here is the quote: Switches build the address table by listening to ...
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How does a switch know when and how to forward traffic to a router

I generally understand how L2 switching works. I want to understand how a switch and router work together to send traffic to a device off the L2 network. For example. Computer A tries to send ...
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Do all devices which use Wi-Fi (802.11) use CSMA/CA?

I know this is quite trivial, but I just want to know if all devices which support Wi-Fi through interface cards/hardware (like laptops/PCs/phones..etc) use CSMA/CA irrespective of their router/...
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What flow control mechanism does ethernet uses?

Datalink layer is basically responsible for 3 major functions - Error detection/correction - CRC is used by ethernet Collision detection - CSMA/CD is used by ethernet But I couldn't find what flow ...
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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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IP datagram route through a network utilizing ARP

Suppose I want to send an IP datagram from node D to node C . Each step I also want to list the MAC addresses of the source and the destination , as well as the source and the destination of the IP ...
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MAC flooding for new host in L2 domain [duplicate]

This hypothetical network has one dumb L2 switch and two hosts A and B connected to it. CAM table entries on the switch are all populated and both hosts have ARP entries for each other. Now if a ...
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Slotted ALOHA efficiency

In slotted ALOHA, the maximum efficiency is 36.8% when only one station transmits in one time slot . My question is, if only one station is transmitting in one time slot, then there will be no ...
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Layering unicast addressing over multicasts

My question has to do with layering of unicast over multicast and has two parts. Part 1. IP unicast over MAC multicast First part of the question is whether there is a standard that prohibits use of ...
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How do hosts filter broadcast signals in wireless network?

In bus/hub network, hosts check the destination address of every broadcasted packet they receive and accept it if they are the destination, otherwise they ignore it. Do we use the same principle in ...
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what's the usage of jamming signal in CSMA/CD?

Take the coxial cable for example, I already understand in CSMA/CD all stations use the same channel to transit data,and if two stations transit data at the same time,a collision occurs and once the ...
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Is TCP aware of MAC adress

lets say I would like to make connection between client and server on port 80. Is 3 way handshake aware of server MAC address? I mean: client send SYN data packet to specific IP:port and MAC. In ...
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Is there any fixed version of CSMA/CA?

I was trying to understand exact algorithm for Carrier Sense Multiple Access / Collision Avoidance mechanism from Forouzan's book. The book gives very detail explanation of topics. However explanation ...
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How to trace the MAC route? [duplicate]

If there have several Switches, they are connected using trunk, and in the end switch there is server on it. So, if there is a controller server on the other end. if the controller trace to the end ...
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Cisco switch SVI MAC address strange problem [closed]

I am having the SVI MAC address problem on my switch (3850) The MAC address of the SVI (VLAN2) is currently conflicting with another switch. Why did this switch decide to use 7018.xxx.xxx MAC ...
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Broadcast Timer [duplicate]

This question is regarding in the process of L2 MAC Address learning. As we know, if a sender sends a packet to some receiver host which switch doesn't know, it will broadcast for learning. Assume an ...
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3 votes
1 answer
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Why the ARP packet contains values like "Physical Address length" etc?

From what i know,MAC addresses are made of 48 bits,while IPv4 addresses are 32 bits Why are there these header fields? Are there MAC addresses with more or less 48 bits?
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Is IP an abstraction

If packets "hop" from network device to network device across networks using MAC addresses, resolved by ARP, does this suggest that IP is essentially an abstraction? By abstraction, I mean, the ...
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What actually is EIFS?

There are a couple of things on the Internet about EIFS intervals. One way I've found to help people understand EIFS is the following: When a station receives a corrupted frame, it has no way of ...
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1 vote
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What is the use of Phy and MAC chip?

Is it mandatory to have a MAC and PHY chip? Are these two chips within a NIC CARD? As I understand, these two chips are connected using RGMII or SGMII or xaui.
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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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To what address does ARP reply in the presence of MAC masquerading

The ARP packet has a duplicate of the sender/destination hardware address. Theoretically, you could have a case where a device sent Layer2: From AA:BB:CC:DD:EE:FF To FF:FF:FF:FF:FF:FF Layer3: ARP ...
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Does MACsec (IEEE 802.1AE) support multicast / broadcast?

In general, Ethernet supports both multicast and broadcast. However, once you start encrypting the payload, you need a key management. I am wondering if IEEE 802.1AE supports multicast and broadcast? ...
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Packet with wrong source MAC address

When I send a UDP packet with wrong source MAC address but with right source IP address, assuming a reply is sent, will I get the reply because I have right source IP address, or I will not get the ...
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7 votes
3 answers
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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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8 votes
1 answer
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Run MACsec and VLAN in parallel?

MACsec (IEEE 802.1ae) adds a security tag to an Ethernet frame and encrypts the IEEE 802.1Q field, the EtherType and the payload field. If you want to use VLAN, you need the 802.1Q field to announce ...
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BGP with x2 sessions and x2 L3 VLANs - Please Explain

I am learning about Cisco BGP networking now and came across an interesting situation. In my examples, there was one which suggested that two VLANs were configured on Layer 3 in order to run two BGP ...
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6 votes
2 answers
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Why is RTS/CTS optional for IEEE 802.11?

In wikipedia it is stated: Request to Send (RTS) frame: The RTS and CTS frames provide an optional collision reduction scheme for access points with hidden stations. A station sends a RTS frame as ...
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Connect to the switch console port, type the keyboard I will get messy code

I follow the Tutorial to connect a switch, use ls *usb* I can find the usb: $ ls *usb* cu.wchusbserial1410 tty.wchusbserial1410 I connect to it: screen tty.wchusbserial1410 9600 but I get the ...
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How might I test layer2 latency over ethernet without a target IP address? [closed]

Is there a way, via standard ethernet layer2 protocols, to test latency to a device without using it's IP address? Background: I have a fibre "box" provided by my ISP physically connected to my ...
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4 votes
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MAC ACL to prevent access to unauthorized computers

My company wanted to prevent rogue PCs from being connected to our network. Network access must be allowed only for our company users and specifically for PCs, Printers.. that are provided by the ...
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How do I send a request to a router knowing the IP address, but not knowing the MAC address?

And what protocol should be used? Thanks.
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MAC address table [duplicate]

I believe this is a very simple question for you, but a interesting one for me, so I hope I don't mind you with my first question here, noob question. We have two switches. SW1 and SW2. First of all:...
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Sending packet through LAN cable to another PC having ip of another network

What happens if, say PC A(192.168.2.2) tries to send a packet to PC B(10.0.2.3) connected through LAN(only 2 computers are connected in this case PC A and PC B) as there is no router or a switch ...
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Cisco Asr1001 not able to receive 2048 macs (arps) in a sub-interface

I´m Brasilian, so excuse me any gramar error. I have a cisco router ASR1001 (IOS XE Version: 03.08.01.S) and I need to connect it to a service provider running BGP ipv4. This service provider gave me ...
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2 votes
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How often does it happen that at the Layer 2 (MAC) an error goes undetected?

I know there are certain error detecting and correcting codes added at the Layer 2. However is it still possible to have errors go undetected eve with the addition of these codes? What type of ...
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In the MAC acronym what do the words Media, Access and Control refer to independently?

I am not a native English speaker and I know what MAC addresses are and how are they used in networks. However what I do not understand is where this words came from independently. What does Media ...
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Is the MAC address pool from which Bluetooth, Wi-Fi, GSM cards etc take their addresses from the same address pool as the ethernet MAC address pool?

I know that most wireless communication devices have a MAC address. I wonder if the pool from which their MAC addresses are assigned is the same address pool from which physical Ethernet devices also ...
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Why do we have to connect through a default gateway in a LAN?

I'm a beginner in networking and I'm looking for answers for these questions: Why do we have to connect through a default gateway when we are connected to a LAN and want to connect to another devices ...
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