Slow Network Issues - Old FreeNAS KB - Archived

[ldkraemer]

Slow Network Issues - Copied from the Old FreeNAS Knowledge Base - So it is archived!

Posted on Tuesday, December 19, 2006 by Tim Fehlman

I had deployed a new network with a server and a number of workstations. Everything worked fine and the network connectivity was there but everything
was painfully slow. All the network applications took forever to come up and file transfers were ridiculous. After about two weeks, I finally discovered the problem.

When I created the images for the workstations, I built the image with the network card set to a speed of 100 Mbits and full duplex. At the last minute, we switched from a managed switch to an unmanaged switch. Most unmanaged switches have their speed duplexing set to autonegotiation. It was at this point that I made a bad assumption.

And I assumed that since the network cards on each workstations were hard coded to 100/full, the switch would automatically recognize this and set each port to 100/full as well. In reality, I had created a duplex mismatch. Essentially, the network cards were looking for a 100/full link on the other end of their patch cable
while the switch was expecting an autonegotiation session. Neither got what they were looking for and trouble ensued!

The long and the short of it is that you have to be sure that what is on one end of a patch cable is the same on the other end of the patch cable. That also goes
for autonegotiation. Both devices need to be set to autonegotiation. If only one is set that way, then you will experience all types of network slowdowns!

So remember:
10 to 10
100 to 100
1000 to 1000
half to half
full to full
auto to auto

Make sure that all of your speed and duplex match on all of your devices.

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From: Ethernet auto-sensing and auto-negotiating Written by Jay Kreibich


Quick Summary:

* Auto-negotiation is not 100% reliable, but it does generally work.

* Links with a duplex mismatch will operate, but will generate large numbers of errors, and can slow down busy networks.

* For most interfaces, both speed and duplex need to be set to auto for full auto-negotiation to work.

* Forcing a Catalyst switch port to a specific speed disables auto-negotiation for the duplex setting.

* Full-duplex mode can be achieved only if both sides of the link are either set to auto-negotiate or manually configured to use full-duplex.

* Full-duplex will work only if a host is connected directly to a switch or other device, with no repeaters or hubs in-between.

* If auto-negotiation is enabled on only one side of the link, it will always default to half-duplex, regardless of what the other side of the link is forced to.

* If one side of a link is forced to full duplex and the other is set to auto-negotiation, a duplex mismatch will occur.

* You can force a new auto-negotiation by simply unplugging a host cable for 10 seconds.

* Most 10 Mb interfaces can run only in 10Mb half-duplex mode.

* Most 10/100 Mb interfaces can do auto-negotiation. Most 10/100 Mb interfaces with RJ-45 twisted pair jacks can run in full-duplex mode.

* Any network connected via an AUI port (with an external transceiver, for example) can run only in 10Mb half-duplex mode.


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Comments:

by Peter Heginbotham:

I think the common wisdom now is to use Autonegotiation unless you have a legacy device.

Some light reading
http://www.cisco.com/warp/public/473/46 ... _tr_10_100 & http://www.sun.com/blueprints/0704/817-7526.pdf


by Bob Jaggard

There have been instances where different vendors, and in one case the same vendor's, products that don't fully and correctly implement Autonegotiation
between themseleves. The impact of this is that even though both ends are configured for Autonegotiation, you may still experience a duplex mismatch.
The absolutley safest way to go is to 'lock and load', that is fix the speed and duplex to be the same at both ends. Where you have one or both ends as
unmanaged hubs or switches, you will usually not have control to be able to do this and Autonegotiation is therefore you only option.


Copied from the Old FreeNAS Knowledge Base so it's archived.


Thanks.

Larry Kraemer