Switches - speed and duplex negotiation with NICs

Billybob,

I hope you don't mind me moving this to a new thread - but I am a little concerned that this is going off subject which will lead to joezep1 not getting his original query answered.

OK - this may confuse the matter further, but as you seem to have quite an enquirying mind , and we'll probably end here any way.....:

Networks are layered. They build up in a strict heirarchy. TCP/IP is about half way up. At the very bottom is the cable passing electrical signals. This electrical signalls are organised into groups and sent from one PC to another. Therefore, before any communication can start the lowest layers have to sort themselves out.

One of the first things to sort out is how fast the electrical signals will be passed from the switch to the computers and which mode will be used. This settings can be set manually, but almost always nowadays these settings are negotiated automatically by the network devices. Basically when you connect a computer to a switch, the first thing the computer will do is see how fast it can talk to the switch and which mode it will use. So it will connect at the slowest connection speed (10Mb/s half duplex), and see if the switch (or other device) will talk to it at that speed. Then the network card will step up a speed and try again until it gets to the maximum speed it can connect at (with a small modern switch this is usually 100Mb/s full duplex, however, if there is a problem on the line {faulty cable for example} you may only get to 10Mb/s full duplex or 100Mb/s half duplex if you get a connection at all. With the latest enterpise switches maximum speed can be 1000Mb/s full duplex).

However, this negotiation process can go wrong. In your case you may well have turned the PC on before the switch had time to complete its start up routines, and in that way it came on line half way through the PCs speed negotiations. This caused the system to hang and you get the problem you describe.

I have seen networks where initial speed negotiations cause problems. A network cards would not negotiate reliably with the switch even though they were from the same manufacturer. It causes all sorts of problems and took a while for me to track it down. We had to swap out the switch in the end - for one from a different manufacturer - bizarre.

Truth of the matter is that really networks are very reliable once you get the configured correctly. They work so well that it is easy to over look just how complicated all the communications are under lying it all.

 

No problem from here.

BillyBob

 

I believe you hit the nail SQUARELY on the head.

I should have known better as I have run into a problem before when my Wife and I would turn both machines on at about the same time. ( had to shut both down and start over )

Another thing I have learned that may mess up the LAN ( but often forget ) just because the HD light shows no action after you turn the machine on DO NOT get in a hurry to do anything. It may well still be working in the background.

This is why I usually turn the machine on as I walk by to get my first cup of AM coffee. By the time I get back it is ready to go.

BTW. It also seems to boot up much quicker that way.

BillyBob

 

BB - in that case, you will probably do yourself a favor by stopping as much of the speed negotiation as possible.

Your network cards will have a setting for speed and depending on the card, may have another for duplexing or it may be combined with speed. The default is 'auto' which leads to the discussion between NIC and switch that Reggie speaks of.

I'd suggest settting each card for the fastest speed/duplex it will run. Try 100Mbps Full-Duplex. If it works, the PC will stay on the network. If not, it will give you a disconnect notice (probably mentioning cable problems) and you can back off to 100Mbps half-duplex, 10Mbps full-duplex, 10Mbps half-duplex in that order until one works.

This will prevent much of the initial conversation and streamline your startup.

High end switches also allow for setting the switch port but most of the home switches we use don't. If yours does, once you have a card speed set, put the switch port to the same speed from auto.

More explanation on terms

- speed is pretty simple and will be either 10Mbps (mega bits per second) or 100Mbps for equipment you are likely to use at home. The giga-bit stuff (1000Mbps) is expensive and serious overkill for a home network.

- duplexing sets for one way or two way data streams at any given time. Half-duplex means the card is either transmitting or receiving but never both at the same time. Full-duplex means the card can both send and receive at the same time.

Thus 10Mbps half-duplex is the slowest option for modern networks, 10Mbps full-duplex is slightly over twice as fast, and so on. I say 'slightly over twice as fast' since with half-duplex transmissions, there is additional info sent saying when a transmit is done so the other party can switch from receive mode to transmit mode.

Additional note for anyone using a hub for their network - replace it with a switch if possible because:
- low end hubs (most you will be likely to have) can only run at 10Mbps half-duplex so that's the fastest your NIC can be set. Switches can easily run 100Mbps full-duplex.
- low end hubs can offer a maximum bandwidth of 10Mbps and will divide it among the connected devices so it is possible with a 10 port hub, all ports in use, all devices trying to transmit or receive for each device to only be given 1Mbps to work with. Switches can provide a full 100Mbps to each connected device.

It is possible for a switched network to run at over 200 times the speed of a network that uses hubs because of the speed/bandwidth pieces mentioned above and also because a switch is 'smarter' and there will be fewer collisions on the switched network but that would be a discussion for another time. In practice, just expect a loaded switched network to run at least 10-20 times faster, at a minimum, than one that uses hubs.

 

WOW WOW WOW !!

I can say nothing other than " I appreciate the time and effort that you folks have put in. "

Newt
I may very well have a go at your suggestion about setting the NIC speed. ( just gotta find out where to do it ) I am printing out your reply as I write as I have not digested all of it yet.

I will start with the 3rd machine which is the oldest and slowest. If that one works out the other two sure should.

As to the Hub vs Switch. Thanks for posting the great info.

I have a Linksys 5 port Switch Model EZXS55W . I am liking it better than just the Router because it does provided more info ( via the lights ) as to what is going on. I was just going to plug the Printer into it but I am gald that I changed my mind.

To Quote my Dad

And I have gotten some very good and very welcome answers.

BillyBob

 

I have been looking around and I need to ask. ( before I mess up 4 a change )

Are the suggested changes for the card settings made in the Properties for the card in Device Manager ?

It looks to me as if it is when I see the various settings available under the Advanced tab.

And they are for the card itself and have nothing to do with IP addressing.

BillyBob

 

And also.

If I do make a mistake the only thing that will happen is that I will not be able to get to the Network or the Internet ?

BB

 

I checked out the NICs on the 2 98SE machines. ( in Device Manager ) and there are no choices to make.

On this XP Pro SP2 there are choices to make. It is the only one that has the advanced Tab. The others only have General, Driver & Resources.

Is this due to an older card ? A driver Problem ? Or the OS ?

I am not too awfully worried as all it working quite well, And the Switch ( according to the lights ) says they are running 100mps Full Duplex.

BillyBob

 

The speed settings are via properties on the NIC.

 

Well right wrong or indifferent I have set the NIC in this XP Pro machine to 100Mbps Full-Duplex. It stayed on.

Both LAN & Internet seem to be just fine.

Again I say thank you.

OH BTW. What about changing the title of this thread to make it point more toward the subject and not make it look as if it related to just me.

I think overall it may help more users because it does contain A lot of very good info and explainations as to how things works.

BillyBob

 

All three machines now have their NIC set to 100Mbps Full-Duplex. Just had to find where to make the changes. In XP I could do it from Device manager. On the 98SE nachines I had to go though Network in Control Panel. And believe me all three were a bit different.

But overall it seems to have improved the speed and smoothed things out a bit.

BillyBob

 

Nice straight forward description of half-duplex and full-duplex. And I thoroughly agree with you that giga-bit kit is over the top for most networks. Perhaps a gigabit connection from your main server to the core switch, or a gigabit back bone on a large network, but for most networks it's over the top.

However....

Haven't we had this argument before ?

I disagree. I would contend that the majority of people looking for advice here are running very small networks. Commonly three or four computers at most. For them a switch is no faster than an equivalent hub. Whereas it is a general rule of thumb that a switch is better than a hub, on a small quiet network you will not see any speed improvement by changing from a 100Mb/s hub to a 100Mb/s switch. In fact you may even get a loss in performance.

A switch has to take in a large part of the network packet and then make a decision on the information it reads in that packet before it starts transmitting the packet to the destination computer. A hub starts transmitting as soon as it starts receiving the packet. A hub latency is significantly lower than that of a switch.

It is only when the network starts to get busy that the advantages of a switch come into play. On a SOHO (small office/Home office) network for the vast majority of time the network will not be busy enough for you to see the advantage of a switch.

I've been burnt by this. Going into a company and advising them to replace their huds with switches, only to find the network was slower with the new switches. It turned out that network traffice was low, and latency was a more significant factor on network performance than bandwidth.

If you are buying new, buy a switch - you'll find it hard not to as few manufacturers sell hubs, and they do a very good job. If your network performance is an issue and when you analyse the traffic it is regularly greater than 5%, look to replace the hubs with switches.

But if you have a network that is working perfectly well with hubs - DO NOT replace them with switches just for the sake of it.

Also if you are on a very tight budget, and you get the chance to buy a cheap 10Mb/s hub (significantly less than a cheap switch) buy it. It will do the job perfectly well. If you have a small network and most of your network use is connection to the internet, your broadband connection is the bottle neck (2Mb/s at most) not the 10Mb/s hub.

Switches are good. But that does not mean hubs are bad. Hubs are good. Switches are better in many circumastances.

Oh and before I forget - if you are installing a business network, invest in managed switches. The fault finding tools they provide are well worth the additional cost.

 

Done

 

Glad to hear it.

The speed improvement is not just confined to start up. The connection speed will be better every time you initiate a new communication over the network.

However, for general use I'd leave auto-negotiation on. Why you may ask! This type of tweak means more work for the network administrator. If you put an old machine on the network, you are going to have to remember to change the speed of the port at the switch if the old machine only has a 10Mb/s NIC. If the line gets noisy -cable starts to fail, or you move a noisy (electrical noise) device near the cable - the system will not be able to cope automatically by dropping the network speed. If you swap your cable ports around, you have to remember to change the switch configuration to match. If your switch fails and you have to get the network back up in a hurry and all you can get hold of is a hub, you'll have to remember to reset all the network cards to half duplex (or back to auto).

So Billybob, for you switching the manual speed and duplex is right, but generally the increase does not warrant the increased administation overhead of doing the tweak IMHO.

 

First off. I believe this post is well worth the space it takes up.

And thanks for renaming it.

I think we have found that out already. My Wife and I played Cribbage between the two machines. Some of the first words she spoke were " WHAT DID YOU DO ?" When I asked why she said. " This has NEVER played this fast. "

But I may have ( note I said MAY have ) a problem. When testing things out I had problems getting the Printer to print from the other two machines. But that may not be due to the change I made. I have had the problem before.

Or could it be that the Printer just had to adjust to the new settings ?

ReggieB
If I read ( interpet ) correctly what you write you are syaing that even though at the time things are working great, there could be times when the change to the Manual setting could create a problem by not being able to adjust ?

Or ( indirectly ) that if I do run into problems I should know were to look first.

BillyBob

 

Yup ReggieB - we have had the switch vs. hub discussion before and as always, your points are well taken.

Truthfully, I'm not sure how a person would go about finding a new low-end (low-cost) hub in the US these days.

 

I agree with both your points - always enjoy our discussions and your points, and it would be hard to find hubs nowadays except for some very cheap second user bargins.

My main point was that I don't think people should rip out their existing hubs just for the sake of it. Golden rule of networking - if it ain't broke, don't fix it.

 

With further testing I find that the printer works just fine on a freshly booted machine. ( A fully powered off boot that is not just a Windows Restart. ) HMMMM !! I believe that is telling me that there may be some miss-behaving, or corrupted in some way or even incompatable software on that machine. Which is possible because some of it goes way back to the days of Win95. And maybe even before. Can't blame the NIC or the change I made for that.

I also had some Internet problems last evening. Both connecting and staying connected. But I can not fully blame the NIC change for that either as it also is nothing new.

But overall I believe that NIC setting change has made a great improvement in both WWW and LAN usage.

Normally I fully agree. But I saw a chance to experiment with something new and report the results of same. Hopefully not only to gain knowledge for myself ( which has been done BIG TIME ) but to help others also. ( which I hope will be).

Networking is getting to be a bigger and bigger thing.

BillyBob

 

Perhaps that is the paradox of the Network Administrator: If you don't experiment, you don't learn, but experimenting causes unforseen problems. The more you fiddle, the more likely you are to mess it all up, but if you have learnt from fiddling you won't be able to sort out the mess ups.

And as much as you experiment with "test" systems, it's not until they go live that you really learn who good they will be.

Perhaps that is the measure of a good Network Administrator - they learn what they can play with, and what to leave well alone.

 

I have a media server that stores MPEG2 files that average 1 Gigibyte in size.
I edit these videos on my desktop with Pinicle Studio 9 so I have to move the file over to my desktop for editing.
I had a 10/100 hub between the machines and it was horribly slow.
I changed it to a 10/100 switch and it was better but still slow.
Both PCs have the Asus P4P800 motherboard with intigrated Marvel gigabit NIC.
I ordered a DLink 5 port gigibit switch and replaced the 10/100 switch.
The diffrence in speed was night and day!

This switch was 60 bucks (us dollars)
http://www.newegg.com/app/ViewProductDesc.asp?description=17-111-020&depa=0