Is the Network-Connection "healthy" ?

by Johannes Helmig [Published on 7 Dec. 1997 / Last Updated on 7 Dec. 1997]

One of the Windows95-command-line utilities allows to check, whether the network is "healthy" or not, by analyzing network statistics:

NET DIAG /
STATUS

You are prompted for the computer name , just hit <Enter> for your local system. If you have multiple network boards (and a Dialup-Adapter does count as a network-board) you are prompted to select one of the Network-numbers (in my configuration, 0 is the Dialup-adapter, 7 the NE2000 Ethernet-board):

The report then shows:
- how long was the network adapter operational (in my case: 5 min )
- network packets transmitted and received
- retransmittions (circled in green)
- collisions (circled in red)

Collisions:
Ethernet is often also described as : CSMA/CD network
Carrier Sence - Multipe Access /Collision Detection

Connected stations listen to the network-wire for a valid "carrier Signal".
If there is no communication in progress, station are allowed to access the network, where is can now happen that multiple station try the access at the same time, causing a signal collision, which is then detected and avoided by retrying to transmit after a random delay.
Therefore, there will always be some collisions on a network, as long as more than 1 system is using the network. As long as the ratio of collisions to transmitted packets is just a few percent, don't worry.
However, if that the ratio of collisions to Transmitted packets goes above 10%, then your network cable is simply too busy, you need to rethink your network layout by adding more cable-segments, multiple network boards into your servers and bridges, filtering network traffic between cable-segments.

Retransmittions:
This number should be very low, because retransmittions indicate a problem on the network: that the signal/packets gets damaged during transmission, so that it does not get recognized by the destination system and has to be (after a time-out period) to be retransmitted). This is usually causing a network slow-down (see also The Network is slow !).
Check your network : cable-length, T-connectors, Terminators.

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