More LAN speed issues...

Hi folks,

I posted here some time ago about speed problems I was having with my
LAN. I've done more reseach since, but I still have problems. All
sensible advice gratefully received...

I have slowly been building a domestic 100Mbps wired LAN using donated
hardware. Upstairs there is a twelve port 3Com SuperStack 3000 100Mbps
switch, connected to which is this machine running Windows XP Pro, a
Windows 98SE machine, a Linux server running Samba etc, and an IPCop box
providing WAN firewalling, DHCP/BOOTP services etc.

In turn, the 3Com switch is connected to a 100Mbps, 24 port Netgear
switch downstairs, to which is connected my girlfriend's PC and a box
used for music playback through the hi-fi, both running XP Pro.
Everything works as you'd expect, but *slooooooooooowwwwly*, sometimes,
which is my problem.

Some connections are acceptably fast - 50Mbps is okay, and I've seen as
much as 75Mbps during tests, but as little as 10Kbps is a joke!

I have been using iperf with a 60 second transmission time on both Linux
and Win XP to test various links. Here are a few examples:

My XP Box -> 3Com Switch -> Linux server = 50.1Mbps
Linux server -> 3Com Switch -> My XP Box = 635Kbps

Music XP Box -> Netgear Switch -> 3Com Switch -> Linux Server = 1.44Mbps
Linux Server -> 3Com Switch -> Netgear Switch -> Music XP Box = 294Kbps

Music XP Box -> Netgear Switch -> 3Com Switch -> My XP Box = 2.01Mbps
My XP Box -> 3Com Switch -> Netgear Switch -> Music XP Box = 42Mbps

All the link indicators I can find show a 100Mbps connection. All the
operating systems are pretty much at 'factory default' settings - I
can't be sure about the switches, though. A few simple experiments with
upping the TCP window size to an arbitrary 200KB made no difference one
way or the other on the two slow connections I tried.

These speed issues have shown up some weird behaviour when transfering
files with the SMB protocol - transfering a directory of FLAC files on
the route My XP Box -> 3Com Switch -> Netgear Switch -> Music XP Box,
there will be a 30sec pause, then a file will fly at 40% link speed,
then another 30sec pause, followed by another file at 40%, and so on.
Transfering a large CD image on the route My XP Box -> 3Com Switch ->
Linux Box, goes at rought 5% for the first 30secs, and then blasts along
at 50%. *shrug*

So, can anyone give me a few clues on where to go from here?

I suspect it's a configuration issue I haven't discovered yet, but can
it be something as stupid as a couple of semi-faulty cables?

Does anyone recognise these symptoms - a link roaring along at 50% link
speed in one direction, but the same link crawling at 1% in the other
direction?

Can someone guide me towards a tool that will give me lower-level link
diagnostic information for an ethernet network? How far down through the
layers do I have to go before I discover whether or not communication is
being inhibited at the physical layer?

Any other ideas? I'm not doing anything particularly outlandish here -
the biggest inhibition to a successful outcome is my ignorance...

Many thanks as always,

PJ.

On Fri, 02 Mar 2007 21:27:39 +0000, PJ <(E-Mail Removed)> mused:

>Hi folks,
>
>I posted here some time ago about speed problems I was having with my
>LAN. I've done more reseach since, but I still have problems. All
>sensible advice gratefully received...
>
>I have slowly been building a domestic 100Mbps wired LAN using donated
>hardware. Upstairs there is a twelve port 3Com SuperStack 3000 100Mbps
>switch, connected to which is this machine running Windows XP Pro, a
>Windows 98SE machine, a Linux server running Samba etc, and an IPCop box
>providing WAN firewalling, DHCP/BOOTP services etc.
>
>In turn, the 3Com switch is connected to a 100Mbps, 24 port Netgear
>switch downstairs, to which is connected my girlfriend's PC and a box
>used for music playback through the hi-fi, both running XP Pro.
>Everything works as you'd expect, but *slooooooooooowwwwly*, sometimes,
>which is my problem.
>
I haven't read everything properly yet but why do you need 2 switches?

I'd ditch the 3 com, move the Netgear upstairs and run the 2 machines
downstairs through the 1 cat5 cable, or add another if possible. To
run 2 connections through 1 cable google for 'cable econmiser' or
similar.
--
Regards,
Stuart.

Lurch wrote:
>
> I haven't read everything properly yet but why do you need 2 switches?

Flexibility. Greater scope for future expansion. To cut down on the
number of cables required. Because the guy with the most gear wins...


> I'd ditch the 3 com, move the Netgear upstairs and run the 2 machines
> downstairs through the 1 cat5 cable, or add another if possible. To
> run 2 connections through 1 cable google for 'cable econmiser' or
> similar.

Indeed. Why? There is no reason why my present configuration shouldn't
work, is there? Ditching a switch would definitely be a retrograde step
to my mind - I don't want to do it unless there's a sound technical
reason...

.... and yes, I know a lot of people hate 3Com stuff. I'm not sure that's
a sound reason, though - if the 3Com switch could be proved to be at
fault, and to be incurable, then maybe...

Thanks,

PJ.

On Fri, 02 Mar 2007 22:17:15 +0000, PJ <(E-Mail Removed)> mused:

>Lurch wrote:
>>
>> I haven't read everything properly yet but why do you need 2 switches?
>
>Flexibility. Greater scope for future expansion. To cut down on the
>number of cables required. Because the guy with the most gear wins...
>
Yeah, to a point. You can do as I said though and run 2 machines
through 1 cat5 so that part of the argument falls down.

More equipment = more points of failure.

>> I'd ditch the 3 com, move the Netgear upstairs and run the 2 machines
>> downstairs through the 1 cat5 cable, or add another if possible. To
>> run 2 connections through 1 cable google for 'cable econmiser' or
>> similar.
>
>Indeed. Why? There is no reason why my present configuration shouldn't
>work, is there? Ditching a switch would definitely be a retrograde step
>to my mind - I don't want to do it unless there's a sound technical
>reason...
>
I see no reason to do either, it was just my first thoughts after
glancing throuhg the thread.

>... and yes, I know a lot of people hate 3Com stuff. I'm not sure that's
>a sound reason, though - if the 3Com switch could be proved to be at
>fault, and to be incurable, then maybe...
>
My 3com switch (left over from a job) has the occasional glitch when
negotiating a link speed. IT usually works, but sometmes throws a
wobbly when pluggin a device in\powering equipment off\on.

As you say though, if it works, leave it. There's no need for you to
alter anything for the purposes of testing even, we'll test it all
from inside this group, because we can do that you know.
--
Regards,
Stuart.

Lurch wrote:
>
> Yeah, to a point. You can do as I said though and run 2 machines
> through 1 cat5 so that part of the argument falls down.

Yeah, but only two. When I start building my disc-less Linux
thin-clients for distributed audio in the kitchen and elsewhere, then it
becomes a hurdle I have to deal with...

.... and then there's distributed video. That'd be fun - TV on demand, no
more sticking your head around the living room door when you're working
in the kitchen...

> More equipment = more points of failure.

Indeed. Although, for the time being, I'd rather learn how to manage and
deal with it, rather than shy away from it. There are LANs where my
configuration is the only viable solution - I'd rather learn how to
administer such a system...

>> ... and yes, I know a lot of people hate 3Com stuff. I'm not sure that's
>> a sound reason, though - if the 3Com switch could be proved to be at
>> fault, and to be incurable, then maybe...
>>
> My 3com switch (left over from a job) has the occasional glitch when
> negotiating a link speed. IT usually works, but sometmes throws a
> wobbly when pluggin a device in\powering equipment off\on.

Interesting. How does the wobbly manifest itself? No link? Whole router
seizes? My 3Com is up 24/7, but there's plenty of stuff plugged into it
that gets powered up/down every day, including the Netgear switch...

My 3Com switch can be administered remotely. There's a console port on
the back, but it's also possible to use in-band telnet. I don't know
what the default IP address is, though - the manual says it'll use BOOTP
if there is a service available on the network, which there is, but an
nmap scan of the whole LAN doesn't find it. I will end up having to
obtain a null modem cable to go in via the console port, unless you know
another way of resetting/altering the IP address for 3Com switches...

> As you say though, if it works, leave it.

But it only kinda works. I'm a programmer, not a network administrator -
half the reason I'm building a more elaborate network than I really need
is to learn a little more about network administration and debugging. It
may well be ignorance on my part, but I kinda expected this part of the
project - simply plugging the gear together - to go without a hitch,
given that I'm not try to do anything more elaborate than get a 100Mbps
TCP/IP based LAN up and running. I expected the factory defaults to work
just fine - maybe that's wrong.

Ta.

PJ.

On Sat, 03 Mar 2007 11:29:31 +0000, PJ <(E-Mail Removed)> mused:

>Lurch wrote:
>>
>> Yeah, to a point. You can do as I said though and run 2 machines
>> through 1 cat5 so that part of the argument falls down.
>
>Yeah, but only two. When I start building my disc-less Linux
>thin-clients for distributed audio in the kitchen and elsewhere, then it
>becomes a hurdle I have to deal with...
>
>... and then there's distributed video. That'd be fun - TV on demand, no
>more sticking your head around the living room door when you're working
>in the kitchen...
>
I see. Personally I'd try and run everything back to 1 point and have
1 switch, but there's no reason why it shouldn't work with 2 switches
stacked.

>> More equipment = more points of failure.
>
>Indeed. Although, for the time being, I'd rather learn how to manage and
>deal with it, rather than shy away from it. There are LANs where my
>configuration is the only viable solution - I'd rather learn how to
>administer such a system...
>
>>> ... and yes, I know a lot of people hate 3Com stuff. I'm not sure that's
>>> a sound reason, though - if the 3Com switch could be proved to be at
>>> fault, and to be incurable, then maybe...
>>>
>> My 3com switch (left over from a job) has the occasional glitch when
>> negotiating a link speed. IT usually works, but sometmes throws a
>> wobbly when pluggin a device in\powering equipment off\on.
>
>Interesting. How does the wobbly manifest itself? No link? Whole router
>seizes? My 3Com is up 24/7, but there's plenty of stuff plugged into it
>that gets powered up/down every day, including the Netgear switch...
>
Usually it just doesn't want to connect or works for a bit then drops
the connection\starts losing traffic\throttles itself.

>My 3Com switch can be administered remotely. There's a console port on
>the back, but it's also possible to use in-band telnet. I don't know
>what the default IP address is, though - the manual says it'll use BOOTP
>if there is a service available on the network, which there is, but an
>nmap scan of the whole LAN doesn't find it. I will end up having to
>obtain a null modem cable to go in via the console port, unless you know
>another way of resetting/altering the IP address for 3Com switches...
>
Yours is better than mine then, don't think there's any adminning to
do on mine (can't remember though, it's in a cabinet in the garage).

>> As you say though, if it works, leave it.
>
>But it only kinda works. I'm a programmer, not a network administrator -
>half the reason I'm building a more elaborate network than I really need
>is to learn a little more about network administration and debugging. It
>may well be ignorance on my part, but I kinda expected this part of the
>project - simply plugging the gear together - to go without a hitch,
>given that I'm not try to do anything more elaborate than get a 100Mbps
>TCP/IP based LAN up and running. I expected the factory defaults to work
>just fine - maybe that's wrong.
>
I do neither, I just fit the stuff and leave it for some else to
administer\program everything, unless I'm feeling really bored!
--
Regards,
Stuart.

Lurch wrote:
> On Sat, 03 Mar 2007 11:29:31 +0000, PJ <(E-Mail Removed)> mused:
>>> My 3com switch (left over from a job) has the occasional glitch
>>> when negotiating a link speed. IT usually works, but sometmes
>>> throws a wobbly when pluggin a device in\powering equipment
>>> off\on.
>> Interesting. How does the wobbly manifest itself? No link? Whole
>> router seizes? My 3Com is up 24/7, but there's plenty of stuff
>> plugged into it that gets powered up/down every day, including the
>> Netgear switch...
>>
> Usually it just doesn't want to connect or works for a bit then drops
> the connection\starts losing traffic\throttles itself.

Interesting. That's not too dis-similar to what I'm experiencing.

I've just managed to kick my girlfriend off her PC long enough to
install iperf and run a few tests - on the route XP -> Netgear -> XP, I
got 73.8 Mbits/sec in one direction, and 81.2 Mbits/sec in the other,
which is *much* more like it. Talking to the Linux box upstairs through
both the Netgear and the 3Com, traffic was down to 4.35 Mbits/sec at best...

So the 3Com is starting to look guilty, despite passing 50Mbps
sometimes. Question is, is it the switch, or is it the cable?


> Yours is better than mine then, don't think there's any adminning to
> do on mine (can't remember though, it's in a cabinet in the garage).

Mine is a rackmount job - I was given it by an even worse tech-hoarder
than me, whose wife had finally lost patience...

It is quite a cool bit of kit with a lot of interesting configuration
options, which is why I'm slightly reluctant to let it go. I need to get
into it to see if I can tweek the setup to eliminate the problems...

PJ.

On Sat, 03 Mar 2007 12:19:16 +0000, PJ <(E-Mail Removed)> mused:

>Lurch wrote:
>> On Sat, 03 Mar 2007 11:29:31 +0000, PJ <(E-Mail Removed)> mused:
>>>> My 3com switch (left over from a job) has the occasional glitch
>>>> when negotiating a link speed. IT usually works, but sometmes
>>>> throws a wobbly when pluggin a device in\powering equipment
>>>> off\on.
>>> Interesting. How does the wobbly manifest itself? No link? Whole
>>> router seizes? My 3Com is up 24/7, but there's plenty of stuff
>>> plugged into it that gets powered up/down every day, including the
>>> Netgear switch...
>>>
>> Usually it just doesn't want to connect or works for a bit then drops
>> the connection\starts losing traffic\throttles itself.
>
>Interesting. That's not too dis-similar to what I'm experiencing.
>
>I've just managed to kick my girlfriend off her PC long enough to
>install iperf and run a few tests - on the route XP -> Netgear -> XP, I
>got 73.8 Mbits/sec in one direction, and 81.2 Mbits/sec in the other,
>which is *much* more like it. Talking to the Linux box upstairs through
>both the Netgear and the 3Com, traffic was down to 4.35 Mbits/sec at best...
>
>So the 3Com is starting to look guilty, despite passing 50Mbps
>sometimes. Question is, is it the switch, or is it the cable?
>
If it were me, I'd get some of those cable economisers (I usually have
some in stock anyway) and move the Netgear upstairs and temporarily
ditch the 3com, just to test. See what speeds you get then over a few
days or whatever.

>> Yours is better than mine then, don't think there's any adminning to
>> do on mine (can't remember though, it's in a cabinet in the garage).
>
>Mine is a rackmount job - I was given it by an even worse tech-hoarder
>than me, whose wife had finally lost patience...
>
Mine's rackmount, but just a basic 10\100 switch, no management
capabilities though, AFAICR. I might have to go and have a look now,
you've got me thinking! A short while ago I had the option of fitting
this one or a Netgear one in a rack on a job, kind of glad I didn't
fit this one as it would have been a nightmare for non-chargeable
callouts!

>It is quite a cool bit of kit with a lot of interesting configuration
>options, which is why I'm slightly reluctant to let it go. I need to get
>into it to see if I can tweek the setup to eliminate the problems...

Might be worth a look, if possible I'd try resetting\defaulting it
first of all.
--
Regards,
Stuart.

On Sat, 03 Mar 2007 12:19:16 +0000, PJ <(E-Mail Removed)> wrote:

>Lurch wrote:
>> On Sat, 03 Mar 2007 11:29:31 +0000, PJ <(E-Mail Removed)> mused:
>>>> My 3com switch (left over from a job) has the occasional glitch
>>>> when negotiating a link speed. IT usually works, but sometmes
>>>> throws a wobbly when pluggin a device in\powering equipment
>>>> off\on.
>>> Interesting. How does the wobbly manifest itself? No link? Whole
>>> router seizes? My 3Com is up 24/7, but there's plenty of stuff
>>> plugged into it that gets powered up/down every day, including the
>>> Netgear switch...
>>>
>> Usually it just doesn't want to connect or works for a bit then drops
>> the connection\starts losing traffic\throttles itself.
>
>Interesting. That's not too dis-similar to what I'm experiencing.
>
>I've just managed to kick my girlfriend off her PC long enough to
>install iperf and run a few tests - on the route XP -> Netgear -> XP, I
>got 73.8 Mbits/sec in one direction, and 81.2 Mbits/sec in the other,
>which is *much* more like it. Talking to the Linux box upstairs through
>both the Netgear and the 3Com, traffic was down to 4.35 Mbits/sec at best...
>
>So the 3Com is starting to look guilty, despite passing 50Mbps
>sometimes. Question is, is it the switch, or is it the cable?
>
>
>> Yours is better than mine then, don't think there's any adminning to
>> do on mine (can't remember though, it's in a cabinet in the garage).
>
>Mine is a rackmount job - I was given it by an even worse tech-hoarder
>than me, whose wife had finally lost patience...
>
>It is quite a cool bit of kit with a lot of interesting configuration
>options, which is why I'm slightly reluctant to let it go. I need to get
>into it to see if I can tweek the setup to eliminate the problems...
>
>PJ.
Swapping the switches around might be a useful troubleshooting
exercise.
Robert

"PJ" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> I posted here some time ago about speed problems I was having with my LAN.
> I've done more reseach since, but I still have problems. All sensible
> advice gratefully received...

Have you tried forcing duplex modes (using ethtool on Linux and the network
card properties on Windows)? These are normally automatically negotiated
like the link speed, but with some combinations of equipment this appears to
go wrong. If the device at one end of a cable is half-duplex and the other
end is full-duplex then you get erratic and slow TCP connection speeds.

If a duplex mismatch is the problem then you will be able to see
Ethernet-level error and TCP retransmission counters both increase as you
transfer data, although a cable problem could give the same symptoms. Also,
you might find that pinging is reliable when the network is otherwise idle
but you get significant packet loss during a transfer.

HTH,
Alex