Questions tagged [ethernet]

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

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602 views

Long Reach Ethernet

In our corporate headquarters we are looking at replacing a 20+ year old phone system and making the switch to VoIP. This is a high rise where we have some limits around options for cabling. ...
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1answer
9k views

Calculate the FCS number from a frame ethernet

I've the following frame ethernet: 08 00 20 0A 70 66 08 00 20 0A AC 96 08 00 45 00 00 28 A6 F5 00 00 1A 06 75 94 C0 5D 02 01 84 E3 3D 05 00 15 0F 87 9C CB 7E 01 27 E3 EA 01 50 12 10 00 DF 3D 00 00 20 ...
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2answers
3k views

Full Duplex and Collision Domain

I have a very basic query on Collision Domain and Full Duplex Mode. There are two types of logical topology: Ethernet and Token Ring . Whenever we read about Ethernet the first thing that we are ...
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1answer
4k views

What is the effect of SVI MTU on Catalyst 6509?

I have some ports on a Catalyst 6509 set to MTU 9216. Some of these ports belong to port channels with a displayed MTU of 1500. I also have a great number of VLANs set to 1500 and not 9216. This is ...
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1answer
4k views

What is the correct way to determine SFP+ Direct Attach cable compatibility between switches and NICs?

I'm contemplating a 10 Gigabit link between an Intel x520 NIC and a Cisco SG500X switch. These two would be within 5m of one another, so using one of the Cisco SFP+ passive Direct Attach cables like ...
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1answer
203 views

What functionality does 802.3bd-2011 actually add to 802.3 Ethernet?

Looking for various documents and the IEEE standards, I can see that 802.3bd-2011 adds a MAC control frame for priority-based flow control. How does priority-based flow control differ from IEEE 802.1P/...
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1answer
197 views

Industrial machines lose connectivity when one is powered off

I am working with 2 identical industrial machines with multiple Ethernet switches per machine. The basic layout looks like this: Switch 1 Machine A -> Switch 2 Machine A -> Switch 4 Machine A ...
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2answers
4k views

How does a layer-2 switch work with UDP?

If UDP and/or TCP send packets via IP to an Internet Protocol Address, how can a layer-2 switch forward these? Is this possible or do you need a layer-3 switch?
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1answer
17k views

What is the voltage used in ethernet lines (UTP Cables)?

I am asking this because after doing some research I found some conflicting information. First, on Wikipedia page on Ethernet physical layer I found that the voltage on the lines is 2.5V. https://en....
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206 views

I need the functionality of a pair of patch panels but I don't want to run one cable per port

My needs will be met by two patch panels with dedicated copper running between them for each port. But I'm looking at a few hundred ports and I'd rather not have to run a few hundred cables. ...
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1answer
6k views

UDLD state: tx/rx loop detected

Relevant Log messages Feb 1 03:39:08.338 EST: %IPV6-4-DUPLICATE: Duplicate address FE80::212:44FF:FE4D:4400 on GigabitEthernet8/20 Feb 1 03:39:08.904 EST: %UDLD-SP-4-UDLD_PORT_DISABLED: UDLD ...
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Physical layer errors in Ethernet

What happens if an error is detected at the lowest possible layer of the stack ISO/OSI for Ethernet? For example, considering 100BASE-TX, it is implemented with a 4B5B coding this means that there ...
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1answer
1k views

How does the preamble synchronize other devices receiving clocks?

As I know the preamble of an Ethernet packet consists of a 56-bit pattern of alternating 1 and 0 bits. But how exactly it helps the other devices to be synced?
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1answer
507 views

Is it acceptable to run Cat 6 along the top of lighting trunking?

In our factory, we have lighting trunking running above the factory floor, which contains electrical cables and has fluorescent lights hung off the underside. It goes everywhere and could potentially ...
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1answer
156 views

Will using phone lines (RJ-11) in place of ethernet (RJ-45), in this case, be detrimental to performance?

My company has begun leasing new office space, and our modem was installed in a room without ethernet, a little ways from the router. There is a bundle of unused telephone lines (RJ-11) which run ...
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1answer
983 views

IGMP snooping in iptv

Host1 wants to join Multicast group as IGMPv3 include (G,S). The same group and source Host2 send as Exclude(G,S) report. what process done in switch?
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2answers
310 views

Bridging LAN networks privately in office environment

I've begun looking into network bridging, must most of it is witchcraft for me so far. I currently have the following setup: I use PC 1 as my development station and PC 2 as a deployment/test station....
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2k views

How does a host in one subnet know to forward the packet to the router MAC, when trying to send a packet to another subnet

I am trying to understand the ARP protocol and I could not understand the above. Consider the topology as follows: H1(1.1.1.1) - (1.1.1.0)R(2.2.2.0) - H2(2.2.2.2) My understanding is that if the ...
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3answers
1k views

How is data sent from multiple different sources (computers) to the same destination host (computer) on a local network is handled by switch?

Let us say I have switch S, to which I have connected 4 hosts (A, B, C and D). Now let us say hosts A and B both want to send a series of data to the same host D at the same time. So here, A and B are ...
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2answers
1k views

How many pps (64Byte each) i can receive in 1Gbps throughput modem / firewall

I need help with this: If i have 1Gb/s throughput. I can receive how many pps in 64Byte each packet / s? Let's say I can send (Packet / Second - 64Byte) 450,000, meaning I would not only have 230.4 ...
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4answers
380 views

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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3answers
191 views

The recommended settings for giga ethernet connected to Ethernet port

What is the recommended duplex and speed configuration for giga ethernet port connected to legacy ethernet (10 mbps) port and there is no available duplex command available on the ethernet side? If ...
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2answers
2k views

May frame reordering occur on Ethernet connection through switches/bridges?

Assumption for flow: Ethernet connection between two nodes through switches/bridges only Either of: No VLAN (802.1Q) header VLAN having same ID and priority (same PCP, DEI, and VID) May frame ...
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2answers
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How does Ethernet Switch ensures the validity of the MAC address table?

Let us say I have switch S with 4 ports, PA, PB, PC, and PD, to which I have connected 4 hosts, A, B, C and D with the MAC addresses AA:AA:AA:AA:AA:AA, BB:BB:BB:BB:BB:BB, CC:CC:CC:CC:CC:CC and DD:DD:...
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3answers
18k views

Whats the difference between VTP and DTP

I am preparing for CCNA and i came across both VTP and DTP. It seems confusing. Are they both trunking protocols to trunk interfaces? But the modes are different for each. Can someone explain how they ...
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3answers
473 views

Flow control in networks

Why is flow control implemented in both transport and data link layer? If it is already implemented in the data link layer then what is the need to implement it again in the transport layer.
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19k views

Do I need a 10GbE router to provide 10Gbps LAN speed?

We're planning on creating a 10GbE network for our office. I've got a list of hardware that all support 10GbE, only the router isn't 10GbE: Synology DS3612+ - 12 Drive NAS Intel X540-T1 - 10GbE ...
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2answers
482 views

Is a datagram from an upper network layer converted 1:1 to one of the lower layer?

I know datagrams from upper layers are converted to those of lower layers by adding metadata, but I cannot seem to find this information anywhere. Which one of the below is correct? A single TCP ...
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2answers
16k views

RJ45 Cable only has 4 wires

The cable that connects to my rj45 only has 4 cables, blue, orange, blue stripe, orange stripe. When I connect them to their corresponding ports, there is no internet connection.(Blue = 4, Orange = 6, ...
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550 views

IPv6 Multicast vs Unicast

I'm currently learning IPv6 and they mentioned broadcast is gone in IPv6 and replaced with multicast and unicast. Are there some situations where multicast or unicast is better over the other in ...
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How do the different types of materials used in Ethernet cables affect reliability?

There are many metals used in different types of network cables, such as aluminum and copper. Some are expensive and some are cheap. What scenarios constitute the use of these types of different wire ...
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1answer
2k views

Do we send ack frames in ethernet? if not then how does a router know if its neighbors are down or not?

So first off, do ethernet sends ack frames or not? if it doesn't : then how does a router know whether its neighbors are down or not? if it does : then is it cumulative ack with an ack timer or one ...
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1answer
515 views

How do data packets travel without merging?

I have been very interested in networking for quite a while, and I have been wondering this question. I've been thinking about this in complete binary, meaning how does a 0 of a data packet not get ...
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4answers
9k views

How is TCP duplex if Ethernet is half-duplex?

If I understand correctly, TCP is a full-duplex birectional protocol. However, Ethernet is half-duplex. Does this mean that eventhough TCP supports full-duplex, it only operates in half-duplex mode ...
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1answer
443 views

Lost Ethertype in encrypted MACsec frames

MACsec uses an Ethertype of 88E5. This presents an obvious problem when encrypting frames which already have, or should have, another Ethertype. This RedHat blog, for example, states "[MACsec] can ...
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2answers
3k views

Does Ethernet still use CSMA/CD?

So considering that CSMA/CD is for detecting collisions, mostly in a bus scenario with a lot of stations, then is CSMA/CD still used? Because right now most of the connections are point to point (for ...
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5answers
11k views

Is there a difference between using a cat 6 wall jack vs using a female-to-female connector?

I am running new cat 6 cable from my router to my office so I can get my computer hardwired instead of using WiFi. When looking at what I need to get to connect the cable to a wall plate, I'm seeing 2 ...
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1answer
416 views

Why does 10BASE-T and 1000BASE-TX Ethernet have two Tx signals?

In 10BASE-T and 100BASE-TX Ethernet over twisted-pair cable(for example Cat5e, Cat6a) on PHY level the signals of two endpoints are connected as follows: Tx+ <--> Rx+ Tx- <--> Rx- Rx+ <...
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4answers
2k views

CPU Impact of “debug ip packet” on Cisco Switches

in terms of CPU consumption and possible traffic disruption, what should I generally expect when I run the command: Switch#debug ip packet on a Cisco device in a large ISP network? Cisco devices in ...
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3answers
578 views

A reason why Ethernet has maximum cable length confuses me

The answer in this post suggests that it has two reasons. While the impedance characteristics of a transmission line become less favorable for high speed data as the line gets longer (resistance ...
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1answer
2k views

LACP and how to configure switches correctly

I want to set up a fast network and am considering options. I want a backbone switch that connects all my switches together. I can see options for SFP / SFP+ ports. Some SFP ports are 1 or 2 Gb from ...
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1answer
2k views

Why do we need a crossover cable for 1000BASE-T?

I'm doing course for CCNA and in one lecture teacher showed how to make a crossover cable for Gigabit Ethernet. But as I know Gigabit Ethernet uses all wires of twisted pair cable and each pair is ...
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3answers
828 views

What practices/ mechanisms/ protocols can be used to secure communication on physically exposed Ethernet links?

Given that Ethernet cables are everywhere and use for all kinds of links and it is assumed they are physically guarded, hence typical installations do not leverage any "secure" mechanisms. Let's say ...
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731 views

Cannot access certain web page. Ping succeded traceroute didn't

This is my first question on forums at all. I work as a network support engineer and I have a little issue at work and I would really appreciate advice from you. Cannot access the url www.reach2.org ...
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PPPoE interface doesn't use ARP

LAN border routers often use PPPoE protocol to communicate with ISPs and to access the Internet through ADSL. This link provides an example of output of ifconfig about an interface using PPPoE (page ...
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2answers
10k views

Help optimize a LAG with LACP and two different algorithms on each side

We have a 4Gb (4x1G) LAG trunk with LACP between two cisco switches (c3850<--->c4948) and i am noticing that it is not doing proper load-balancing. I found SW1 using src-dst-ip algorithm and SW2 ...
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2answers
214 views

One ethernet plug, one floor ( 30 workstations )

Got a question about ethernet capacity that I'm unsure of. Moving into a new office, and a problem I phase is that there is only 1 ethernet wall plug on the complete floor. So only way would be to ...
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1answer
999 views

What is Packet Slicing when it comes to Ethernet Switches

I don't think it is a standardized term in the industry and hence different people have different interpretation. When folks in Ethernet Switch world refer to packet slicing, what do they really mean? ...
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1answer
5k views

What is the difference between RJ45 connection standards WE/SS and TE-AMP and when and where are they used?

I recently decided to run some CAT6 cabling and wanted to ensure that my Crimpmaster RJ45 die would work fine for the CAT6A shielded connectors. I noticed that several people had trouble using the ...
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2answers
471 views

Does it work to use CAT6 cable between two CAT5 cables?

I have two Cat 5 cables pre-installed in the walls. I need to connect two rooms, in which each room has its own set of in-wall Cat 5 cables and a slots. Does it work to use a Cat 6 cable to connect ...

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