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Slow Internet On Network

Posted on 2011-10-15
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Last Modified: 2012-06-21
Greetings!

I have inherited a very messy and un-maintained Windows network.

Several servers and workstations are routed through a Cisco PIX 501 which is bridged to a DSL connection.

A brand new DSL modem was installed last week.  Bandwidth at the modem tests just under 10Mbps for downloads and around 800Kbps for upload.  Both are within the expected range.

On the network we experience bandwidth speed tests with downloads consistently around 800Kbps and uploads around 700Kbps.  Up is acceptable, but down is horrible.

I have only recently gained dministrative access to all servers and the PIX as well.  A single (2003) domain controller handles both DHCP and DNS and the network is 10/100.

Short of disconnecting the entire network and moving in component by component, I'm short of ideas.

Thoughts?

Regards,

.adam.
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Question by:akerrigan
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12 Comments
 
LVL 6

Expert Comment

by:Gugro
ID: 36975598
I would recommend to have a look at: "Cisco PIX 500 Series Security Appliances
PIX/ASA: Monitor and Troubleshoot Performance Issues"
http://www.cisco.com/en/US/products/hw/vpndevc/ps2030/products_tech_note09186a008009491c.shtml
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LVL 11

Expert Comment

by:Snibborg
ID: 36975637
Swap your external DNS to OpenDNS.  If you are using the old ISP's DNS with your new ISP connection, this could have an effect on traffic speed.  

Snibborg
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LVL 5

Expert Comment

by:mlchelp
ID: 36976263
make sure proxy arp is turned off on the pix, I have seen this cause this issue in the past. also determin the MTU size of your ISP and set this on the PIX.
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Author Comment

by:akerrigan
ID: 36976316
@ Gugro

Thanks for the article; I've skimmed over it and feel it will be useful.  I'll know more on Monday when I return to the office.

@Snibborg

I've suspected DNS problems.  Internal DNS is generating errors in Event Log.  (I'm getting things cleaned up slow, but sure.)  However, once DNS is established, why would it continue to slow things down?  I'm partial to Google DNS myself and plan to implement it at the Cisco on Monday.

@mlchelp

I'll investigate both of these Monday.

@All

I'm not entirely convinced of the necessity of the Cisco.  I may remove it and put a simple Netgear or Linksys router in place.  We don't VPN, etc. and the configuration of the Cisco seems pretty plain and basic.  I keep thinking of how to simplify the network.  Make sense?

Regards,

.adam.
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LVL 5

Accepted Solution

by:
mlchelp earned 2000 total points
ID: 36976354
adam, that pix 501 is kind of old and yes you can do the same thing with a netgear or linksys but they are not as reliable as the pix. If I were you and didnt want to spend allot of money then yes go with the Netgear or Linksys especially if your only using your internet connection for internet access and your not using vpn or publihing web sites etc. I would buy 2 of them thought and make sure they are configured exactly the same , this wat if one fails you can swap it out without allot of down time. If your company has cash to spend then I would buy a ASA5505, its super simple to configure and rock solid and will perform better than the linksys or netgear.
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LVL 9

Expert Comment

by:gavving
ID: 36977667
Check that you don't have a duplex mismatch problem.  If you look at the config of your PIX, the first couple of lines might look something like:

interface ethernet0 100full
interface ethernet1 100full

Or they may say "auto".  Try changing them to "auto" if they're not already set to "auto".  Check the output of 'show int' to confirm that you're not getting errors on the interface.

But even so, the PIX 501 really isn't a good solution for links over 5mbit or so.  It just doesn't have the horsepower for it.  I'd recommend replacing it with a Cisco ASA 5505.
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LVL 11

Expert Comment

by:Snibborg
ID: 36979592
DNS problems can manifest themselves in less than obvious ways as they can be causing routing issues as they are not operating from a optimal location, especially if you are using the old ISP's DNS servers.

Snibborg
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Author Comment

by:akerrigan
ID: 36980670
@All

Progress!

I've removed the PIX from the mix and installed a fresh Linksys WRT54G router.

Speed at the router is nice: 10Mbps down and 700Kbps up.

However, the slowness on the rest of the network is continuing.  I've verified the IP and MTU numbers with our ISP.  Now I know for certain the slowness is internal and not part of the router.

From my laptop plugged directly into the Linksys, I am pulling DHCP info from our Domain Controller, with DNS also coming from the same server.

I need to now look at the internal network for speed issues.

Thoughts?

.adam.
0
 
LVL 5

Expert Comment

by:mlchelp
ID: 36980877
can you provide more detail, layout, switches etc.
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Author Comment

by:akerrigan
ID: 36980894
@All

Scratch that.

I just found I was testing from the wrong server.

After performing multiple tests from the correct server, as well as a workstation, I'm happy to report our bandwidth experience is top notch!

I consolidated some backbone switches as well, removing a 24 port switch from the network.  (I'm wondering if this contributed as well...)

The problem is solved!

Thank you all for input.

Regards,

.adam.
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Author Closing Comment

by:akerrigan
ID: 36980908
Removed the PIX and added a Linksys router.  Problem solved.
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LVL 5

Expert Comment

by:mlchelp
ID: 36981031
its always the proxy arp or mtu with those devices, it slows down everything
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