27

Some devices could only run at 10 megabit/s, so the device at the other end would autosense the speed to match. If a device that has a maximum speed of 10 Mbit/s is connected to a 10 Mbit/s / 100 Mbit/s switch, the switch needs to lower its speed on that particular port in order to effectively (efficiently) communicate with the device. These ...


14

Remember 10Mbps came first, then 100Mbps, then 1000Mbps. The advantage of supporting multiple speeds and automatically switching between them is you can upgrade your network gradually without having to worry about what speed each device supports or replacing everything at once. You just plug a device in and it connects at the highest mutually supported ...


14

A hub is really just a powered cable that repeats every signal it receives on one interface to all the other interfaces. If two devices transmit at the same time to the receive of the hub interfaces, the hub repeats both signals at the same time to the transmit of all the other hub interfaces, and both signals received will collide at the transmit of the ...


13

To understand this you need to understand the historical context. Originally Ethernet used a shared coaxial cable. Only one device could successfully transmit on this at a time. If two devices transmitted at the same time it was considered a collision. Then repeaters came along, to extend the distance and increase the number of nodes. A repeater would ...


9

Great question. In full duplex, there is a dedicated channel for traffic from "left to right" and a dedicated channel from traffic from "right to left": Therefore, in full duplex, collisions are impossible -- even if both NIC's transmit at the same time. In half-duplex, however, traffic in either direction is meant to only use the wire, one direction at a ...


7

Autonegotiation should only be disabled where necessary. Properly compliant 802.3 hardware will send and respond to information in link pulses. Only in rare instances -- i.e. metro-ethernet -- are link pulses missing. And it is a violation of 802.3. Setting speed/duplex does not disable negotiation; it limits what is advertised. Note: The Cisco 2960S's at ...


7

A 10 Gb NIC connected directly to a 1 Gb either negotiates a 1 Gb connection, or it doesn't work at all. You cannot have the situation you describe unless you have something like a switch in between, where the 10 Gb NIC connects to a 10 Gb switch port. It is very easy to search and find ethernet speed negotiation on the Internet, such as the Wikipedia ...


6

In reality, the legacy 10 Mbps ethernet interface probably can't negotiate, and it can probably only do half duplex (very few 10 Mbps interfaces can do full duplex). You should let the 1 Gbps interface auto-negotiate. It will try to negotiate, but if the 10 Mbps can't negotiate, it will detect (not negotiate) that the connection is 10 Mbps, and it will set ...


6

Your thought process is based on faulty assumptions. By splicing 1 to 3 and 2 to 6 (which is what you have done), this does not put them in the same collision domain. Nor does this cause the devices to autonegotiate into half-duplex mode. Connect only one side of your main cable to one device and what you have now created is basically a "loopback." Look ...


6

You were closer than you think to getting it working. In fact the problem may have simply been that flow control wasn't enabled on the switch. The ethtool source code (rev 3.18) and a register interface for a part I'm familiar with, reveal an explanation for the behavior you observed. The 802.3x standard defines flow-control, but I haven't looked there in a ...


6

With twisted pair and a repeater hub, the hub is not much more than a digital amplifier. For that it senses a carrier from an incoming signal on one port and switches all other ports to output mode. In this output mode, any additional incoming carrier is a collision. This triggers a jam signal to propagate the collision and make the sender stop transmitting. ...


5

Most of this doesn't matter, ethernet flow control has never been widely supported and most switch devices will respect PAUSE frames, but not send them. That being said, your questions can be addressed fairly easily: Not exactly. You can still send pause frames, but your card won't respect ones sent by the switch (which you will likely never get anyhow). ...


5

Two devices operating at different set speeds will not link. If only one side is auto, they may link, but it depends on the specific device(s) as some require the link-pulse information while others will cycle through speeds to get a link; and in the absence of link-pulse information, they will default to half-duplex. (Note: the non-negotiating side may have ...


5

The very short answer: don't configure anything. Auto negotiation (or the lack thereof as Ron's detailed) works only when it's left alone. Manual settings can very easily cause problems either right away when done incorrectly or later on when hardware is upgraded. For 1000BASE-T, auto negotiation is required - most hardware won't allow you to manually ...


5

For 10BASE-T and 100BASE-TX, the MDI side (NICs, routers) transmits on pairs 1-2 and receives on 3-6. On the MDI-X side (hubs, switches) the pairs are swapped. In general, concentrators use MDI-X pinout while edge devices (from the L2 segment perspective) use MDI pinout. Whether the link uses full or half duplex doesn't matter. Auto negotiation takes only ...


5

If you disable Auto Negotiation (AN) you need to make sure that both sides are configured in exactly the same way. There's isn't any point in doing that manually, actually, so you should have AN active at all times. If the duplex settings of the link partners don't match you've created a duplex mismatch. The half-duplex side detects massive collisions and ...


4

With gigabit endpoints (1000BASE-T) your injector needs to be gigabit capable as well. Cheap injectors insert power on the pairs unused by 10BASE-T and 100BASE-TX while disrupting the data transmission on these pairs. This only works when one of the endpoints falls back to 100BASE-TX - while this is quite common it's not to be taken for granted. The ...


4

By manually setting the speed and duplex on one side with automatic detection on the other side, the side with automatic speed will detect (not negotiate) the correct speed. For the duplex, negotiation will fail. This results in the side with automatic duplex set to the default duplex for the speed. The default duplex for 1 Gb is FULL, and for 10 and 100 ...


3

Auto negotiation is performed on the physical layer - the NIC driver may report what has been negotiated or it may not (only speed). If you want to look deeper into this I see two variants: Use switch ports that can be configured to "Auto-10", "Auto-100" and so on. This setting doesn't deactivate autoneg on the switch but restricts the port to only ...


3

I'm not sure about the IEEE standard, but Avaya switches only support autonegotiation for 10/100/1000 Mpbs. Autonegotiation isn't supported for 10 Gig connections. This guy breaks it down a little bit. http://networkn3rd.wordpress.com/2013/04/15/10g-auto-negotiation/


3

Because it's only for your own use, I guess that a simple hack will work. You can build a regular 4 way tap and bridge the listening ports using an old 100mbps Hub to your laptop.


3

The router/switch you are plugging into should negotiate with the card. If you are plugging into a managed switch, you will likely be able to hard code the port's speed/duplex. In a Cisco device this would look like so: Switch# conf t Switch(config)# int fa0/0 Switch(config)# speed 10 Switch(config)# duplex half


3

Half-duplex mode in Ethernet still uses 2 pairs. The difference to full-duplex is that it only uses one pair at a time. Half-duplex mode with twisted pair cables only exists because of hubs: Reason for half-duplex mode in Ethernet? half-duplex mode support in Ethernet chipsets was crucial in case either a network hub (hub is internally a single wire) or ...


3

Suppose machine A starts sending data to machine B. As the packet begins to be sent, machine C starts sending different data to machine B. There is only one signal path to machine B, so the transmissions from A and C collide and B cannot possibly receive both of them. The fact that a different circuit is used for transmissions from machine B, to machine A, ...


3

You simply cannot mix shielded and unshielded parts in a link. The shield only works if it continuous end-to-end and properly grounded on both ends. The actual wires in shielded cabling cannot meet specifications without working shielding. Having unshielded connectors means that the shielding is broken on the link, and it is not properly grounded. ...


3

With rare exceptions, disabling Auto Negotiation is not a good idea. Auto Negotiation (AN) is mandatory for 1000BASE-T and faster. It should stay enabled generally. Disabling it makes a default node (configured with AN) fall back to half duplex - so forcing 100M full duplex on one side causes a link partner with default configuration to connect using 100M ...


3

It's important to understand that the cases where auto-negotiation should be disabled ARE VERY RARE. Many times study material for tests are a bit out of date. Virtually all equipment manufactured in the last 20 years is fully compatible with auto-negotiation. As @zac67 and others have pointed out, early implementations had some incompatibilities. But ...


3

There's Auto Negotiation and that's it. Both sides advertise the speeds and modes they support and the best mutual mode is chosen. The cable is not tested. If the cable quality doesn't support the chosen speed, transmission errors and even repeated link loss have to be expected. The rare exception are "smart-rate" ports for 2.5/5 Gbit/s (and often ...


2

A network connection has dedicated TX and RX pairs, and so the signals do not "collide" during this process. Collisions occur when the two devices operate in a half-duplex CSMA/CD environment. When one device is transmitting on TX, if it receives any sort of signal on the RX it will register this as a collision, stop transmitting, back off and start the ...


2

Short answer is no. Link speed and duplex negotiation is between a NIC and a port on a network (usually a switch port) not with the network itself. Collisions can only occur once you have established your connection to the network and are attempting to transmit a frame.


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