Network problem

[Stephen Ingham]

A repeater is more complicated than a "line amplifier" as Chris described it
below.



The following is a quote from "Cabletron Systems - Ethernet Technology
Guide" Page 7-4.


"Auto Partition

When the repeater detects 32 consecutive collisions on one port it will
logically turn off or segment the port that it detected the problem on, thus
allowing the rest of the network to function properly. When the repeater
detects a collision on the segmented port, the collision will not be
forwarded to the other segments of the network, leaving the port in
segmented condition. When the repeater receives a packet on a good port, it
attempts to transmit the packet to the segmented port. If the packet
transmits successfully, the repeater will turn the segmented port back on,
bring it out of segmentation."



-----Original Message-----
From: gnhlug-discuss-admin at mail.gnhlug.org
[mailto:gnhlug-discuss-admin at mail.gnhlug.org] On Behalf Of Chris Brenton
Sent: Thursday, August 28, 2003 8:57 PM
To: Stephen Ingham
Cc: 'Neal Richardson'; discuss at gnhlug.org
Subject: Re: Network problem

Stephen Ingham wrote:
> 
> A good repeater hub will automatically turn off a port when 32 consecutive
> collisions are detected.

Humm. A collision is defined as a system following the Ethernet CSMA/CD 
rules that detects a different bit pattern on the receive pair Vs. what 
it is currently sending out on the transmit pair. Since a hub is little 
more than a line amplifier, it does not "transmit" per CSMA/CD, and thus 
has no way of detecting collisions. If a hub had this type capability, 
we really would not need switching as it would be trivial to retime the 
circuit as well. My guess is you are thinking of a switch or perhaps a 
dual speed hub (which is still a form of a bridge).

> A switch or bridge will also stop all collisions and other errors from
> propagating over the entire network.

Collisions yes, as it resets the transmission timing. Errors, maybe. It 
depends on the switch. Some filter out runts, bad CRC's, etc. Some do 
not. If the switch runs in cut through mode rather than store and 
forward, chances are its not error checking. Most modern switches 
support store and forward, but I doubt the proverbial "everyone" does.


and Neal wrote:

>  My question is this:  Is this normal behavior to have the whole network 
> go down due to a mis wired cable. I can understand the hub not working 
> but to cause the whole thing to crash seams bizarre to me

Seen this as well. It usually only effects all systems located off of 
the same switch and/or router port. Effectively what you did is change 
your ground reference by 5 volts which tends to bum out electrical 
circuits. Lucky you are not swapping a lot of NIC cards. ;-)

HTH,
Chris

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