Questions tagged [ethernet]

For questions relating to Ethernet networking, as defined by the IEEE 802.3 standards.

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What does the naming convention for ethernet standards mean: 1000BASE-T , BASE-TX, BASE-SX, etc.? What is the meaning of the components of the name?

I understand the number in the naming convention. The number represents how many Megabits per second can the standard support. However, I do not understand the rest of the naming convention. What do "...
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2answers
3k views

Extend MACSec encryption over provider bridge

I already asked this question on SF, but figured it might be a better fit here. Is it at all possible to extend MACSec encryption over a provider bridge? Will the typical 802.1ad implementation be ...
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4answers
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speed/duplex mismatch

How do mismatches occur; what is the impact of a mismatch on network connectivity; is resolution of mismatches really worth the effort; what are some ways to detect mismatches on a large scale?
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How does a switch know where to route packet, when there is another switch in front of the destination?

I am just wondering how a switch does know how to route packets to destinations "hidden" behind another switch. In my understanding a switch has a table that maps each of its hardware ports to exactly ...
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2answers
621 views

Why is adapter ARPing something it already knows?

I don't get why a machine on the network is asking the gateway for its MAC address when it already knows its MAC address: So here you can see the machine MAC ***80 (IP ..*.115) asks the gateway (...
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4answers
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Raw-Ethernet Frames

Recently I was puzzled by the following articles about Raw-Ethernet frames: RAW ethernet vs. UDP Message Passing Using Raw Ethernet Frames Briefly, both of them discusses that it is possible to ...
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1answer
7k views

If two NICs are bonded and connected to different switches how does a router decide which switch to forward the packets to?

I am trying to understand how the architecture works in case of NIC Bonding. The scenario is: There are 2 NICs on the same system. Both are bonded to support failover and load balancing. Hence the IP ...
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3answers
10k views

Why don't switches rewrite mac-addresses?

Is there any particular reason why Ethernet switches don't change the MAC address of a packet? Is it for end host identification using the MAC address, or anything else?
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Do Bluetooth Devices have MAC address with the same specification as the MAC addresses of the Ethernet and Wi-Fi Network cards?

I recently found out that ZigBee devices have MAC addresses. ZigBee is more related to Bluetooth from what I know rather than Ethernet or Wi-Fi. Do Bluetooth devices such as phones, headphones, ...
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Can a switch that does not support VLAN process traffic from a Trunk that is not the native VLAN

Recently encountered a setup where the engineer had a Multilayer Cisco switch with a trunk carrying VLAN 41 to an HP switch that did not support VLANs. What should the HP switch do with the 802.1q ...
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What can cause “FastEthernet is up, line protocol is down” on a Cisco Switch?

I wonder what can cause the first line output of the command show interfaces to be: FastEthernet is up, line protocol is down. In other words, Is the cable that is connected to the local interface, ...
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578 views

Ultra-Fast Querying Using UDP Packets

I am implementing a system where one device on a network queries at a very high frequency (hundreds or thousands of queries per second) through sending a small UDP packet with 8 or so bytes of data. ...
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6answers
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Do network adapters read incoming bits in a single stream?

When a Gigabit network adapter is receiving data, how is it receiving the bits? Is it seeing it all in one stream of 0's and 1's? Or is there somehow multiple streams of 0's and 1's coming in at the ...
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1answer
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How can a TCP window size be allowed to be larger than the maximum size of an ethernet packet?

I know that TCP window sizes can be scaled to over 64KB, but looking at an ethernet packet datagram, such as this one: it looks like a layer 2 packet is limited in size to be much smaller than that. ...
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What purpose is the Uplink port in layman's terms and do I need it?

I have an old Linksys switch (EZXS55W) and it has worked fine for many years now, but I tried to hook something up today to the last open port and noticed the device didn't work when I did this. When ...
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AP3602 with rcvk9w8 image throws “%CDP_PD-2-POWER_LOW: All radios disabled”

We recently bought some new AP3602Es from Cisco. I'm trying to understand why this AP will not turn on the radio when we are sending enough power to the AP. I'm using inline power from the switch, ...
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3answers
24k views

What is the purpose of an Ethernet magnetic transformer, and how are they used?

I have been told that Ethernet magnetic transformers are used for base-t Ethernet when transmission is sent over a lengthy cable. What is the purpose of the transformer? (is it for signal filtering or ...
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3answers
21k views

Assign an IP address based on switch port

Short: I want DHCP server to assign a preconfigured IP address based on a port (on a switch, ideally) a device is connected to. Long: My situation: I am building an automated indoor farm (for ...
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3answers
5k views

Why one of the pairs on Ethernet is not adjacent?

I know that Ethernet over twisted pairs have two standards as the figure below: The pairs are twisted to avoid cross-talk. But why in both standards there is one pair that is not adjacent (pin 3 ...
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1answer
221 views

How sensitive is TDMoE to BER?

We are currently looking at connecting two Asterisk servers across a Metro Ethernet. This leads to a couple of questions I haven't been able to find answers to elsewhere. The first involves bit ...
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2answers
734 views

Multi-drop Cat5e/6 Cable?

I'm looking to install ethernet ports in a small business. There are 7-8 groups of cubicles each with 4 desks. Ideally I'd like to run a cable to each desk but if my math is correct I'm looking at ...
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1answer
228 views

Extra long ethernet, or similar technology, for kite

I just need to have a webcam and some equipment on a kite, running on Ethernet. But unfortunately the string will be more than 200 meters long so Ethernet will not work, (as far as I know). Transfer ...
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1answer
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Is 'switchport protected' supposed to block unicast flooding?

Does having switchport protected configured on an interface prevent unicast flooding for a MAC address the switch hasn't learned? The information that I'm seeing conflicts -- the wikipedia page on ...
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8answers
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Can Ethernet frames only be transmitted in a LAN?

In the LAN depicted in the picture below, am I correct in saying that devices do not have IP addresses? There is no router and also only Ethernet frames (with source and destination mac address would ...
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4answers
17k views

The maximum length of CAT6 for intranet network?

Recently I purchased CAT6 cable with a length of 150 meter. I bought another CAT6 with a length of 148 meter. I joined both the cables using RJ45 cable coupler. I tested it using LAN TESTER, and ...
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2answers
12k views

Difference between LLDP and LLDP-MED

What is the difference between LLDP and LLDP-MED? Is LLDP-MED an add-on to LLDP or something completely different?
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4answers
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NMap: Failed to open device eth1

EDIT: I Have found that Nmap can work in unprivileged mode. A question related to that can be found here. I recently installed NMap 6.49BETA4, and the ZenMap GUI, on my Windows 7 Home Premium x64. ...
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3answers
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MTU vs MSS? When to change MTU and when to change MSS?

Here is the question. When and Why do we decrease MSS instead of MTU. In the router that we can configure can configure both of them separately. Suppose I have kept MSS as 1260.I have not made any ...
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3answers
10k views

Network Byte Order

According to big endian byte ordering or network byte order the bits are transmitted in this order: bits 0-7 first, then bits 8-15, then 16-23 and bits 24-31 last. Does this means that bits from ...
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2answers
17k views

Why is the ethernet payload fixed between 46 and 1500 bytes?

Can anyone explain why the ethernet payload size is fixed between 46 and 1500 bytes ? I read so many articles never get the clarification?
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1answer
645 views

Is ADSL's UDP packet forwarding rate strictly linear to packet size?

Suppose an ADSL2 Annex A device had a upload speed of 300kbps; tested using a TCP connection. Now suppose I want to send 8-byte UDP keep-alive packets at the maximum possible rate*. Would the ...
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1answer
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Remote sniffing with ERSPAN to the desktop

I know how to use both SPAN and RSPAN. If I'm not wrong, ERSPAN leads us to the possibility of remotely monitoring a router through an IP network and a GRE tunnel. However a tunnel end-point is needed....
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137 views

TDMoE and QoS considerations

As mentioned in the previous question I am looking at sending voice communications over a Metro Ethernet connection shared also by data connections. In addition to the previous question I have this ...
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2answers
5k views

How is IEEE 802.1ad (aka VLAN Tagging, QinQ) valid, when the packets are too large?

Recently i've been dealing with MTU issues. And it all seems to stem from the fact that the ethernet adapter on newer computers default of a frame size of 1504 bytes: >netsh interface ipv4 show ...
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4answers
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How do I set up a VLAN between an ESXi VM and Physical Hardware? [closed]

First of all, I am a total noob. The extent of my VLAN experience is setting up a guest network on a wireless router. I have recently gotten a request to set up a public network requiring filtering ...
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1answer
1k views

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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1answer
2k views

Something is filling my force10 ARP table

I have 2 force10 s25 switches that are used for a dark fiber link between two school buildings. One of my switches is filling its ARP table to the brim and then failing. This can happen as often as ...
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3answers
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1000Base-T Ethernet limited to 100 m, why?

In 1000Base-T Ethernet connection, why is there a 100 m link length limit? CSMA/CD links normally are limited to a few hundred meters because of the limitations that CSMA/CD implies (collision domain ...
8
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1answer
279 views

Upgrading our Network to Managed Switch with Internet Routing

I am a business owner with multiple BT Buisness Broadband lines. We have two sets of VOIP lines and two sets of PC's, each with there own switch board. The problem that we have is that our lines go ...
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4answers
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Why is the Ethernet Connection Symmetric?

I know that cable connection (DSL) is asymmetric, there is a certain bandwidth on the channel, and for a better user experience, they allocate a bigger portion to the downstream. I suppose Ethernet ...
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3answers
4k views

Why can a packet sniffer in an Ethernet LAN obtain all packets sent over the LAN?

Why can a packet sniffer in an Ethernet LAN obtain all packets sent over the LAN? In a limited broadcast environment, such as in many Ethernet LANs, a packet sniffer can obtain all packets sent ...
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4answers
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Are multiple links with different VLANs between two switches possible?

I'm not considering Etherchannel or LACP. Given 2 Ethernet switches A and B, where both switches have port 0 configured as a tagged trunk for VLAN 100 and 101 and port 1 configured as a tagged trunk ...
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4answers
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Minimum ethernet frame is 64 bytes, Why the payload must be padded to at least 46 bytes

What is reason to pad payload to mininum 46bytes, to form a ethernet frame of 64 bytes. Following says min would be 41 bytes. https://stackoverflow.com/questions/14526139/what-is-the-minimum-packet-...
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Why preamble is not considered a part of the Ethernet Header?

If I search where does my data start in an Ethernet frame, I get a common answer which says TCP header( 20 bytes) + IP header ( 20 bytes) + Ethernet header( SA + DA + Type) i.e 14 bytes. So, in short ...
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2answers
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What exactly is IPoE?

I am familiar with PPPoE but getting confused with the term IPoE. Is this same as usual ethernet with DHCP server? Does this have any auth built-in? How do I get authenticated? What can a client ...
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1answer
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Mixing Cisco STP Features: BPDU Guard, BPDU Filter, PortFast and PortFast Trunk

I have two switches (Cisco 2960's) with a trunk between them (two ports in an ether-channel) and each has a trunk up to a separate router, all other switch ports are access ports to end devices; R1 ...
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2answers
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Why does 1000BASE-T need Auto-MDIX?

A 100BASE-TX PC interface sends out its frames on pins 1,2 and receives frames on pins 3,6. If we connect this PC's NIC with that of another PC we cannot use a straightout cable, because the frames ...
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2answers
6k views

What's the difference between Ethernet link and Serial link?

Sometimes we see router connected use Ethernet link, sometimes use Serial link, what's the difference between them? and in what scenario we use them?
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2answers
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Why are ethernet / mac -addresses in hex and ip numbers in decimals?

Why are ethernet- / mac-addresses in hex (and have 48 bits) and ip numbers in decimals (and have 32 bits)? Does that have historical or practical reasons?
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3answers
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How does Ethernet detect a collision in the CSMA/CD method?

I understand that Carrier Sense is essentially the NIC "listening" to the medium for any transmissions, Multiple Access means that multiple devices on the network can "listen" to the medium, and ...

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