Cisco 870 router seems to be swallowing bandwidth!

Unanswered Question
Jan 30th, 2008

Hi Folks,

We have just moved into new premises and are using a Cisco 870 router to connect via BT Business Broadband (ADSL) to the Internet.

The line should be able to support up to a 4MB connection but when I run a speed test (e.g. using I'm getting speeds down at the 150K mark! The PC running the speed test is connected directly and exclusively into the back of the router (so there are no other devices conflicting and the PC isn't going via a switch).

The router itself seems to think it has negotiated over 4MB of bandwidth: the result of "router#show dsl int atm 0" yields 5248 kbps.

As a test I set up a Netgear DG834 in place of the Cisco and that was completely happy to supply 3 ~ 4 MB as reported by the speed test site on the same PC connected in the same way.

So ... in my VERY inexperienced view I am fairly confident the BT line is OK but it seems that the Cisco is doing "something". Do you folks have any ideas what that "something" might be? Where do I start looking? What further information do you need to help diagnose this issue? Apologies if this is posted into the wrong forum, could you advise me where I should post it in that case?

My networking / router experience is limited (I'm "comfortable" with the complexity of the Netgear but the Cisco is just another level!) so bear with me if I don't understand any jargon in your answers.

Thanks, Andy

I have this problem too.
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a.cruea1980 Wed, 01/30/2008 - 07:08

A posted config would help greatly.

Did you happen to configure it with SDM or via the CLI?

andygray75 Wed, 01/30/2008 - 07:49

Hi a.cruea1980,

Thanks for your response. The router was configured using SDM.

I've attached a (mildly) filleted config. Let me know if you need some of the filletings put back.

andygray75 Tue, 02/05/2008 - 06:12

This issue has now been resolved. Thanks to all those that responded.

Using the website and using the "port 80" option it was observed that the router was slower when just handling port 80 traffic. This led to an investigation of the firewall but nothing conclusive could be drawn from the configuration. The router was then factory reset and reconfigured from scratch testing the speed at each opportunity. It was eventually observed that the firewall settings were too strict causing it to inspect "too many" packets. This slowed the router down so much that it could not handle legitimate traffic quickly enough. By lowering the overall firewall settings the router could process traffic more quickly and the speed was restored!

Hope someone else finds this useful and doesn't need to reset their router, too!


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