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Slow internet

Posted on 2011-10-04
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Last Modified: 2012-05-12
I have a problem where my Internet is really slow. If I bypass the firewall and plug my computer directly in it works fine. I have had a problem in the past caused by a chattering nix but that slows down network traffic as well. Network traffic is fine. Any suggestions?
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Question by:jamiebehl
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Expert Comment

by:owner66
ID: 36912061
What type of firewall?
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by:Sid_F
ID: 36912082
I had an issue with my home internet access, I changed the mtu size on the firewall and this did the trick. A good tool to use is mturoute.exe. run this when the pc is directly connected to the web, it will tell you the max mtu size then set your firewall to same value http://www.elifulkerson.com/projects/mturoute.php
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Author Comment

by:jamiebehl
ID: 36912238
It is a Cisco Firewall.  If I plug directly into the firewall the internet is fine.  I have over 100 devices on the network.  I don't have managed switches so I can't determine speeds.  I was looking at using some product such as Wireshark to try and determine the problem.  
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Expert Comment

by:Rob Williams
ID: 36912512
Slow how? Is it slow opening web pages or slow downloading a file? If the former your internal DNS server may be using DNS forwarders that are not current. If so update them with the ones issue to the PC when connected directly.
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Author Comment

by:jamiebehl
ID: 36912531
It is slow doing both of those.  I ran a speed test and we are getting .10 mbps when we usually get 10mbps.

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by:Rob Williams
ID: 36912551
Wireshark would be your best bet then, but to use it you need to have a managed switch and be able to do port mirroring so that you can see the traffic and capture it. Thinks like streaming media by a few users can really "chew up" a lot of bandwidth. It can be time consuming to pinpoint.
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Author Comment

by:jamiebehl
ID: 36912554
I don't have any managed switches on my network.  Do I not have any other options?
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by:Rob Williams
ID: 36912621
One option is to find an old hub (not switch) and put it between the firewall and your users. You can then plug your monitoring PC into the hub and see the traffic. Hubs broadcast all traffic to all ports, where switches are much more efficient and send the traffic only to the port to which it is destined.

You can also by a network tap as another possibility:
http://www.barracudanetworks.com/tap/overview/

Might your Cisco support port mirroring?
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by:owner66
ID: 36913103
You could get into the cisco firewall and see if any particular ip address(s) are using alot of connections.
Also could unplug patch cables for all machines, test internet, plug in a machine, test internet, plug in 2nd machine etc.
You will get to a machine that slows it down.
Tedious i know.
ds
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by:ddiazp
ID: 36913123
go into the firewall and do:

show interface ethernet0
show interface ethernet1

(or whatever interfaces you use for inside/outside)

make sure speed, duplex look good, make sure there are no drops, CRC errors, runts, etc.

If all looks good, check:

show traffic
show xlate count

and look for suspicious behavior
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by:IT-Monkey-Dave
ID: 36913195
Make sure every interface in the path to the Internet under your control is running Full Duplex.  Don't trust the duplex indicator lights on the hardware to be correct (assuming there are any visual Duplex indicators).  I've seen this happen repeatedly where the duplex LED is on and the devices say they're running Full Duplex, but they aren't really.  Sometimes this happens when you've hard-configured for Full.  Try Auto-Negotiation of speed and duplexing instead.
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Expert Comment

by:Rob Williams
ID: 36913437
Please do not lock any NIC's speed or duplex. You do not have managed switches and switch ports and NICs must be the same. Your switch only has auto, so the NICs must remain at auto.
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by:ChiefIT
ID: 36933796
That may be the problem Rob:

I know that Cisco has a problem if the duplex settings don't match, it can't negotiate the duplex settings well. Maybe going to the router and changing it to Auto negotiate the duplex settings will fix this issue.
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by:ChiefIT
ID: 36933813
I know we had a problem with the cisco switch duplex settings and the router duplex settings mismatching, (or was it our access and core switches that mismatched)? Nevertheless, I would see five minute disruptions and timeouts in internet connectivity.
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Author Comment

by:jamiebehl
ID: 36933818
The network here is not labeled at all.  The previous IT staff didn't label anything.  :(  I have narrowed it down to 1 port in the Comm closet but when I unplug it from the switch it controls 6 different rooms and 20 plus computers throughout the building.  ?!?!?  I don't think it is a chattering NIC because it just affects the internet traffic.  I'm not sure how to determine which computer is the culprit.

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by:IT-Monkey-Dave
ID: 36933851
I've run into this duplexing headache with Cisco and SonicWALL hardware.  Check this carefully.
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Author Comment

by:jamiebehl
ID: 36933868
I've eliminated the Cisco Firewall from the equation.  I bypassed it and still had the problem.  I'm assuming it is an infected machine that I can't pin point.  There must be a switch in the ceiling or something connecting all of these sporadic rooms.
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Expert Comment

by:Rob Williams
ID: 36934390
My background is in network cabling infrastructure testing. 80% of network perfomance isssues are cabling related. Network cables are not like a phonne cable where if you have connectivity it works. Poorly terminated ends, untwisted pairs, stretched or kinked cables, or proximity to EMI can take a network segment to its knees and yet still show as connected.
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Author Comment

by:jamiebehl
ID: 36945911
I have installed a managed switch where I believe the problem is.  I also traced the cable to where I think the problem is.  It is happening at 9:30 everyday and then stops at some point.  I will update the status tomorrow or the next day when I pin point the problem.
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Expert Comment

by:ChiefIT
ID: 36977091
I believe Rob's original advice was valid and warranted. I think it's a DNS problem. On the server, run DCdiag /test:DNS and post any errors.

NOTE: DCdiag is a member of the server support tools and you can either download it from the internet or install it from the OS install CD's..

http://technet.microsoft.com/en-us/library/cc776854%28WS.10%29.aspx

This advice is, of course, assuming you have a WIN server for domain functions of your 100+ computers...

You are probably using outdated root hints servers..

Since I am only agreeing with ROBWILL, please don't credit me for his solution.
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Author Comment

by:jamiebehl
ID: 36977117
We have a content management server that had a corrupt configuration. We removed it and created a config from scratch. It worked great on Friday. We will see ifi t works tomorrow.
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Expert Comment

by:Rob Williams
ID: 36979627
You are suggesting the content management server was generating a lot of Internet Traffic?
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jamiebehl earned 0 total points
ID: 36981181
The configuration was corrupt.  It is a 3rd party software that has a special configuration.  About 2 weeks ago there was an update.  The update caused some corruption in the configuration.  Once the config was removed and created from scratch all has worked fine.  
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Author Closing Comment

by:jamiebehl
ID: 37010554
I worked with the 3rd party vendor to fix this problem
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