Want to protect your cyber security and still get fast solutions? Ask a secure question today.Go Premium

x
?
Solved

Flow control question

Posted on 2012-09-07
16
Medium Priority
?
958 Views
Last Modified: 2012-09-13
I have different brand managed switch in my network, some of them are gigabyte switch and come are fast Ethernet switches. I am wondering if I should enable flow control on each switch? And for the workstations, many don't have gigabyte nic. can I just leave the nic setting as default? and what else I need to do?
0
Comment
Question by:okamon
  • 7
  • 7
15 Comments
 
LVL 10

Expert Comment

by:Gajendra Rathod
ID: 38377773
Flow control has two disadvantages

1. Congestion Spreading

2. External Head of Line Blocking

Network administrator use TCP retransmission as it allows utilization of the full network bandwidth.

I think, it is better to disable this feature and use TCP retransmission.

In case you need to enable Flow control, it must be configure at machine NIC and switch port used by the machine.
0
 

Author Comment

by:okamon
ID: 38378252
so in my environment I should disable flow control on all the switches and devies? I think the nic default setting are either auto or disabled (so if's auto, do I still need to change it to disabled?)

and where is "TCP retransmission"? I don't see this in my switch setting...
0
 
LVL 30

Assisted Solution

by:pgm554
pgm554 earned 1600 total points
ID: 38384841
Whenever there is gigE involved,set everything to auto period.

Switches and NIC's.

Leave nothing set to manual.

And unless you have ancient switches and NIC's with little or no buffering,not even worth it.
0
VIDEO: THE CONCERTO CLOUD FOR HEALTHCARE

Modern healthcare requires a modern cloud. View this brief video to understand how the Concerto Cloud for Healthcare can help your organization.

 

Author Comment

by:okamon
ID: 38387490
thanks, >>Whenever there is gigE involved,set everything to auto period.
I have all the switches set to AUTO for the speed, but for Flow control, there is only 2 options, either ON or OFF. So I should disable it in my mix environment right?

If I set flow control to disable on switch port, and the connected workstation set to enable, what's going to happen? the switch take precedence?

And for the speed, if I set it to AUTO on switch, but the workstation set to full duplex 100, will the switch use fd100 or it will become half duplex?
0
 
LVL 30

Assisted Solution

by:pgm554
pgm554 earned 1600 total points
ID: 38387592
Do not set the ws nics to manual.
Auto only for EVERYTHING!
It will screw things up royally.

I would turn flow control off.

http://www.smallnetbuilder.com/content/view/30212/54/
0
 

Author Comment

by:okamon
ID: 38389535
ok, so you are suggesting me to set all switches and NIC on each workstaions to AUTO and disable Flow control on both switches and NIC on each workstations.

I think you missed some of my questiosns above, can you still tell me what's goign to happen in the situation?

>>
If I set flow control to disable on switch port, and the connected workstation set to enable, what's going to happen? the switch take precedence?

And for the speed, if I set it to AUTO on switch, but the workstation set to full duplex 100, will the switch use fd100 or it will become half duplex?
0
 
LVL 30

Expert Comment

by:pgm554
ID: 38389588
auto used with  manual duplex fd will cause packet loss(collisions)

This is a bad thing.


http://en.wikipedia.org/wiki/Duplex_mismatch
0
 

Author Comment

by:okamon
ID: 38389595
ok, so basically you are saying they always have to be identical otherwise there will be problem right? ex: auto and auto, full duplex and full duplex, so on...

and how about flow control? same apply?
0
 
LVL 30

Accepted Solution

by:
pgm554 earned 1600 total points
ID: 38389613
Yes

But gig only works correctly when set to auto.

So manually setting the duplex on a gig switch breaks a number of things,so don't do it.

There really is no point in messing with flow control unless you have old hardware,and even then,chances are you won't need it enabled.
0
 

Author Comment

by:okamon
ID: 38389742
thanks. I checked all my switches, the flow control is set to disabled. But I see some hp windows 7 workstations have default flow control set to enabled (see the screenshot)
So should I go aroudn all workstations and make sure they are all set to disabled? will there be any issue if I leave it like this?

flow control
0
 
LVL 30

Expert Comment

by:pgm554
ID: 38391149
If it's not enabled on the switches,shouldn't be an issue.
0
 

Author Comment

by:okamon
ID: 38393363
so the flow control is not the same manner as duplex setting you are saying? so as long as the switch has it diabled, it will ignore the setting on workstation correct?
0
 
LVL 30

Assisted Solution

by:pgm554
pgm554 earned 1600 total points
ID: 38393390
Yes.
It's the switch that controls that protocol,just like jumbo frames.
If it's not enabled,it's ignored by the switch.
0
 

Author Comment

by:okamon
ID: 38397366
pgm554, may I ask you one more question? if the device connected to port 3 is generating excessice CRC/alignment error, will that impact the whole network? or just the performance between the device and its destination? I believe if it's generating broadcast error, then for sure it will impact the whole network... not sure in this case..
0
 
LVL 30

Expert Comment

by:pgm554
ID: 38397393
If this is a switch.that port is it's own collision domain,so all that should be affected is the connection between the two devices.

http://en.wikipedia.org/wiki/Collision_domain

But a CRC on a switch is not a good thing and needs to be looked at.

It's usually a duplex mismatch,but it could be cables too.
0

Featured Post

Free Tool: IP Lookup

Get more info about an IP address or domain name, such as organization, abuse contacts and geolocation.

One of a set of tools we are providing to everyone as a way of saying thank you for being a part of the community.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Make the most of your online learning experience.
This article will show you step-by-step instructions to build your own NTP CentOS server.  The network diagram shows the best practice to setup the NTP server farm for redundancy.  This article also serves as your NTP server documentation.
After creating this article (http://www.experts-exchange.com/articles/23699/Setup-Mikrotik-routers-with-OSPF.html), I decided to make a video (no audio) to show you how to configure the routers and run some trace routes and pings between the 7 sites…
Here's a very brief overview of the methods PRTG Network Monitor (https://www.paessler.com/prtg) offers for monitoring bandwidth, to help you decide which methods you´d like to investigate in more detail.  The methods are covered in more detail in o…

579 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question