Auto Negotiate vs Fixed Speed and Duplex

This thread helped me with problem I had so I will write my experience for future generations…

I had a system with one Compactlogix L35E, three AENTs, OP and SCADA, all connected via ethernet switch Westermo i-Line.
The system lived happily for a few days after set-up. But, few days later I encountered severe communication problems.

RSLogix5000 software became extremely unstable and slow to operate when online with PLC. Scrolling was laggy and general use of application became very tedious.

Few weeks after, RSLinx started to lose connection to PLC and SCADA would go blind for a few seconds every few hours…later on, every few minutes. In RSLogix5000 became impossible to go online with PLC.

Only solution I found was a restart of PLC. Do I need to say that would fix things only temporarily, for a few days/weeks?

Only thing that could be seen as suspicious on my switch diagnostics was collisions on PLC port (<0.5%) and PLC was getting a few FCS errors every now and then.

After reading this thread I examined port speed/duplex and revealed an interesting thing. Both switch and PLC ports were set to auto negotiate, but switch port ran at half speed. I had to manually set the speed on switch to 100/full and all problems went away.

I have set only a PLC port to fixed speed/duplex. AENTs were very unhappy with it and refused to play along. I was unable to get them going without errors on fixed speed/duplex.

So, thank you, forum guys.

I always hate it when I read a forum thread where someone has an issue and their last post is "never mind, I figured it out". Not a very helpful answer for others looking for solutions to the same problem.

It's the posted solutions found and the reasons it did solve a problem that helps provide the answers for others.

Nice to hear that this thread helped you out VXY.

And thanks for the reply letting us know how your problem was solved.

I'm sure others searching this forum for answers to the same questions will thank you as well.

Dave

DGillen said:

I always hate it when I read a forum thread where someone has an issue and their last post is "never mind, I figured it out". Not a very helpful answer for others looking for solutions to the same problem.

It's the posted solutions found and the reasons it did solve a problem that helps provide the answers for others.

Nice to hear that this thread helped you out VXY.

And thanks for the reply letting us know how your problem was solved.

I'm sure others searching this forum for answers to the same questions will thank you as well.

Dave

Click to expand...

Hear hear! Well stated Dave.

Stu....

So what is the recommended setting for AutoNeg or Fixed?

I've read through this thread and can't seem to see a consistent message about what is best practice. I've got two systems that I've worked on for months without any issues and both of them at totally different sites just in the last week experienced the lockup issue.

Both are very small systems without connection to a corp. network.
1 system is Compactlogix L32E to two iFix PCs via a Stratix 2000 unmanaged switch (1783-US08T), the other system is a Compactlogix L32E to a PC running FTViewME also via Stratix 2000 unmanaged switch. I have my laptop on that system as well for Logix config.

Should I be setting PC's and PLC's to 100/Full? Then what about my laptop, do I need to change that every time I go from a corp. network where Auto is probably best to Fixed before connecting to these systems?

And any idea why these systems can run for months without any issue and then just suddenly start having it? I used to have a lot of trust in CompactLogix, but that's been severely shaken these past few days. Total lockups without PING even working don't do much for the confidence factor.

Any insight greatly appreciated.

-Greg

I would propose the following are valid settings:

1. Both sides auto negotiate
2. Both sides fixed to anything, as long as they match (speed and duplex)

This should work, but I would say is not preferred because there is little reason to run at half duplex on current switched networks:

3. One side auto, the other side HALF duplex

Not recommended:

4. One side auto, the other side FULL duplex
5. Both sides fixed at different settings

These are in order as to what some consider to be preferred, though some would allow to swap 2 in place of 1. Since it's a valid setting, I wouldn't argue if someone chooses this. If auto works, I prefer to stick with that and only move off it if there are issues.

robertkjonesjr said:

I would propose the following are valid settings:

1. Both sides auto negotiate
2. Both sides fixed to anything, as long as they match (speed and duplex)

This should work, but I would say is not preferred because there is little reason to run at half duplex on current switched networks:

3. One side auto, the other side HALF duplex

Not recommended:

4. One side auto, the other side FULL duplex
5. Both sides fixed at different settings

These are in order as to what some consider to be preferred, though some would allow to swap 2 in place of 1. Since it's a valid setting, I wouldn't argue if someone chooses this. If auto works, I prefer to stick with that and only move off it if there are issues.

Click to expand...

This thread divulged why no.4 is "not recommended", and I'm having a small chuckle at no.5 !!

But a good summary of the thread, thanks.