Re: [Hampshire] 8% Packet loss due to ethernet cable

2021-03-04 Thread Chris Ellis via Hampshire 
On Thu, Mar 4, 2021 at 6:39 PM Joseph Bennie via Hampshire <
hampshire@mailman.lug.org.uk> wrote:

> Actually the issue is more likely naturally collisions on the network.
>
> I noted that you said ‘hub’ not ‘switch’.
>

It's actually really hard to get hold of a true 'hub' these days.  When
most people say hub they typically mean a switch.


>
> A switch has logic to balance all the traffic, like traffic lights (gross
> simplification).
>
> where as a hub is like all the lights are always green/ no lights at all,
> and you just take your chance crossing.
>
> With a switch when there are more devices on the network it manages a
> controlled degradation, like lights at a roundabout. That leads to slower
> response times but high reliablity.
>
> With a hub : well its pot luck. packets bouce and need to be resent futher
> amplifying the chaos. the more devices. the more chaotic.
>
> so sall that really happened when you changed the cable was the traffic
> settled and the previous collisions cleared.
>

The key difference is a hub electrically copies the incoming data to all
other ports.  It relies on the collision detection of ethernet to deal with
multiple devices trying to talk at the same time.

A switch however is store and forward.  A frame is received, buffered and
forwarded.  With MAC address learning and CAM they can very efficiently
forward frames.  It's also important
to remember that you only get packet loss when links are contended, ie at
100% utilisation.  So all those fancy control features of managed switches
rarely kick in on a well designed network.

An important result of this difference is that it is impossible to have a
gigabit hub, since you cannot electrically copy the signals to all ports
like with fast ethernet.


>
> the other factor might just be old age - simple oxidation of the
> connections
>

I've seen packet loss from an old cable which is straining the connector.
It's good advice not to reuse old cables.

The other thing to be very aware of is most Cat5e cables on Amazon are not
upto spec.  The rating only means something if you can trust the source.
Cheap cables on
Amazon often are CCA (Copper Clad Aluminium) which does awful stuff to high
frequency signals.  You'll find a CCA cable will work for a short run, but
will go out of spec
if longer than about 5m.  It's definitely worth spending the extra 20p and
getting a good cable from a good supplier.


>
> So : a basic switch is probably a wise purchase. :)
>

If anyone genuinely has a hub, not for debugging stuff like LLDP, then I'd
echo replacing it, but I'd be skeptical that any 'hub' brought in the last
10 years is really a hub.

Regards,
Chris
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Re: [Hampshire] 8% Packet loss due to ethernet cable

2021-03-04 Thread Keith Edmunds via Hampshire 
On Thu, 4 Mar 2021 18:39:04 +, hampshire@mailman.lug.org.uk said:

> Actually the issue is more likely naturally collisions on the network.

Changing a cable wouldn't fix that (although I agree with your post in
general).
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Re: [Hampshire] 8% Packet loss due to ethernet cable

2021-03-04 Thread James Courtier-Dutton via Hampshire 
On Thu, 4 Mar 2021 at 12:09, rmluglist2--- via Hampshire
 wrote:
>
> Hi all
>
> I’ve been experiencing some network issues I’ve never seen before (in 20 
> years of (admittedly home LAN) experience).   One of my machines was showing 
> 8% packet loss when pinging the same site as another machine on the same hub 
> at the same time which was reporting 0%.   This proves it had to be a local 
> fault and sure enough – swapping the 8% machine’s cable for a new one 
> resulted in 0% loss.
>
> What I find odd though is why not 0% or 100%?   Surely the wires inside the 
> cable can only break – it wasn’t as if the cable was being moved around – it 
> was stationary.  To lose one packet every 12 or so seems very odd for a cable 
> issue.
>

This can be any number of things.
I have seen intermittent faults on cables that are not moved around.
Or Link lights saying everything is OK, but no packets passing.
As you say, 8% packet loss seems strange, why no 0% or 100%.
You do not say what spec cable and whether you were expecting
10Mbps/100Mbps or 1000Mbps
1000Mbps cable has 8 wires in it. It uses all 8 wires for 1000.
If one of the wires is broken, it might fall back to 100 or 10Mbps.
If you were sending a lot of data across the link, you might start to
see packet loss due to congestion if you were only getting 100Mbps
when you expected 1000Mbps.

Ethernet cable testers are not expensive. You could find out what was
wrong with the cable if you are interested.

Kind Regards

James

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Re: [Hampshire] 8% Packet loss due to ethernet cable

2021-03-04 Thread Joseph Bennie via Hampshire 
Actually the issue is more likely naturally collisions on the network.

I noted that you said ‘hub’ not ‘switch’.

A switch has logic to balance all the traffic, like traffic lights (gross 
simplification).

where as a hub is like all the lights are always green/ no lights at all, and 
you just take your chance crossing.

With a switch when there are more devices on the network it manages a 
controlled degradation, like lights at a roundabout. That leads to slower 
response times but high reliablity.

With a hub : well its pot luck. packets bouce and need to be resent futher 
amplifying the chaos. the more devices. the more chaotic.

so sall that really happened when you changed the cable was the traffic settled 
and the previous collisions cleared.

the other factor might just be old age - simple oxidation of the connections

So : a basic switch is probably a wise purchase. :)

Sent from my iPhone

On 4 Mar 2021, at 14:49, Marc Loftus via Hampshire 
 wrote:


Hi Rob

Ethernet cables should have a quality rating on them. You may have been using a 
Cat 5 cable. Cat 5 have a certain bandwidth and can support 10 or 100 Mbps 
speed. Older cables may work depending on length and interference as you have 
experienced.

Shielding is another concern. If the cable runs near a power cable, some of the 
traffic can be interfered with hence the 8% loss.

I try to use Cat6 or Cat6e cables.   With cat6E you are also future proofing a 
little as well as home routers and network interfaces improve.

Marc

On Thu, 4 Mar 2021 at 12:09, rmluglist2--- via Hampshire 
mailto:hampshire@mailman.lug.org.uk>> wrote:
Hi all

I’ve been experiencing some network issues I’ve never seen before (in 20 years 
of (admittedly home LAN) experience).   One of my machines was showing 8% 
packet loss when pinging the same site as another machine on the same hub at 
the same time which was reporting 0%.   This proves it had to be a local fault 
and sure enough – swapping the 8% machine’s cable for a new one resulted in 0% 
loss.

What I find odd though is why not 0% or 100%?   Surely the wires inside the 
cable can only break – it wasn’t as if the cable was being moved around – it 
was stationary.  To lose one packet every 12 or so seems very odd for a cable 
issue.

As I say, with new cable installed, it’s now at 0% packet loss so all is well 
that ends well but would the issue have been to do with:
a) the length of the cable or
b) the quality of the cable or
c) both?

Cheers
Rob
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Re: [Hampshire] 8% Packet loss due to ethernet cable

2021-03-04 Thread Keith Edmunds via Hampshire 
On Thu, 4 Mar 2021 14:49:03 +, hampshire@mailman.lug.org.uk said:

> With cat6E you are also future
> proofing a little as well as home routers and network interfaces improve.

With the caveat that CAT6e is not a recognised standard, so there's no
guarantee what you're getting.
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Re: [Hampshire] 8% Packet loss due to ethernet cable

2021-03-04 Thread Marc Loftus via Hampshire 
Hi Rob

Ethernet cables should have a quality rating on them. You may have been
using a Cat 5 cable. Cat 5 have a certain bandwidth and can support 10 or
100 Mbps speed. Older cables may work depending on length and
interference as you have experienced.

Shielding is another concern. If the cable runs near a power cable, some of
the traffic can be interfered with hence the 8% loss.

I try to use Cat6 or Cat6e cables.   With cat6E you are also future
proofing a little as well as home routers and network interfaces improve.

Marc

On Thu, 4 Mar 2021 at 12:09, rmluglist2--- via Hampshire <
hampshire@mailman.lug.org.uk> wrote:

> Hi all
>
>
>
> I’ve been experiencing some network issues I’ve never seen before (in 20
> years of (admittedly home LAN) experience).   One of my machines was
> showing 8% packet loss when pinging the same site as another machine on the
> same hub at the same time which was reporting 0%.   This proves it had to
> be a local fault and sure enough – swapping the 8% machine’s cable for a
> new one resulted in 0% loss.
>
>
>
> What I find odd though is why not 0% or 100%?   Surely the wires inside
> the cable can only break – it wasn’t as if the cable was being moved around
> – it was stationary.  To lose one packet every 12 or so seems very odd for
> a cable issue.
>
>
>
> As I say, with new cable installed, it’s now at 0% packet loss so all is
> well that ends well but would the issue have been to do with:
>
> a) the length of the cable or
>
> b) the quality of the cable or
>
> c) both?
>
>
>
> Cheers
>
> Rob
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> Please post to: Hampshire@mailman.lug.org.uk
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www.webmarcit.com
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Re: [Hampshire] 8% Packet loss due to ethernet cable

2021-03-04 Thread Nick Chalk via Hampshire 
Hello Rob.

On Thursday, 04 March, 2021, you wrote
> One of my machines was showing 8% packet loss
> when pinging the same site as another machine on
> the same hub at the same time which was
> reporting 0%. 
...
> What I find odd though is why not 0% or 100%?
> Surely the wires inside the cable can only break

"All signals are analogue, even if they're
digital."

The ethernet cable is a transmission line,
carrying high-frequency signals from the
transmitter to the receiver. Although 100BaseTx/
1GBaseT use twisted-pair, it's little different
from the coaxial cable connecting a television or
radio to its antenna.

Without attaching the cable to a time-domain
reflectometry scope, it's not possible to say what
caused the packet loss. However:

- A fracture in the cable or in an RJ-45/conductor
  joint will block DC, but not the high-frequency
  AC of the ethernet signal. To the latter, the
  fracture will look like a low-value capacitor;
  the signal will be degraded, but not blocked
  completely.

- Ethernet uses forward error correction (FEC).
  Extra bits are added to the transmitted data
  stream, adding redundancy to the data. At the
  receiver, these bits are used to detect
  corrupted data and, if there are not too many,
  recover lost bits. This means that ethernet can
  tolerate a certain amount of interference before
  you start seeing packet loss at the ICMP layer.
  Damage to the cable can make it more susceptible
  to interference - you will not notice until the
  bit errors exceed the ability of the FEC to
  correct it.

For information on how this sort of problem is
measured, have a look at:
   https://en.wikipedia.org/wiki/Eye_diagram

> it wasn't as if the cable was being moved
> around - it was stationary.  To lose one packet
> every 12 or so seems very odd for a cable issue.   

Even if the cable wasn't being moved deliberately,
it was still being influenced by temperature
changes. The resulting expansion and contraction
of the copper and PVC can cause a dodgy joint to
break, or a weak point to fracture.

> would the issue have been to do with:
> 
> a) the length of the cable or 
> b) the quality of the cable or 
> c) both?

Most likely (b). Well-manufactured cables with
good strain relief will still fail eventually, but
they will last longer.

For a short while, I worked for an ISP. A regular
task was to check the ethernet interface
statistics on the routers and switches for rapidly
increasing FEC or CRC errors. That information
would allow us to detect dodgy cables and
interfaces that were on their last legs.

Nick.

-- 
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 Confidence is failing to understand the problem.


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Re: [Hampshire] 8% Packet loss due to ethernet cable

2021-03-04 Thread Brad Rogers via Hampshire 
On Thu, 4 Mar 2021 12:09:21 -
rmluglist2--- via Hampshire  wrote:

Hello rmluglist2---,

>a) the length of the cable or 

Unlikely;  Cable runs of up to 100m should be okay.  Difficult to reach
in a domestic setting.

>b) the quality of the cable or 

More likely.

You also mentioned (lack of) cable movement.  Don't be so sure -
expansion/contraction as temperature changes may play a part.

To say nothing of routing.  Esp. if the cable ever goes under floor or
via the loft.  Then rodents and all sorts of other critters might enter
the mix.

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[Hampshire] 8% Packet loss due to ethernet cable

2021-03-04 Thread rmluglist2--- via Hampshire 
Hi all

 

I've been experiencing some network issues I've never seen before (in 20
years of (admittedly home LAN) experience).   One of my machines was showing
8% packet loss when pinging the same site as another machine on the same hub
at the same time which was reporting 0%.   This proves it had to be a local
fault and sure enough - swapping the 8% machine's cable for a new one
resulted in 0% loss.

 

What I find odd though is why not 0% or 100%?   Surely the wires inside the
cable can only break - it wasn't as if the cable was being moved around - it
was stationary.  To lose one packet every 12 or so seems very odd for a
cable issue.   

 

As I say, with new cable installed, it's now at 0% packet loss so all is
well that ends well but would the issue have been to do with:

a) the length of the cable or 

b) the quality of the cable or 

c) both?

 

Cheers

Rob

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