Slow Speed over Comcast 50 Mb using Cisco 2951

[pkpatel]

Hello,

We have 50 Mb Comcast cable conencted to 2951.  There is another conenction to AT&T 20 Mb circuit which goes thru' an ASA 5510.  Path to Internet is as below.

3750 Stack------Barracuda---------2951------------Comcast

                                                               |

                                                               |

                                                               |

                                                           ASA 5510--------------AT&T

As long as Comcast is up, 2951 sends Internet traffic out to Comcast and uses AT&T via ASA for backup.

When traffic goes over Comcast, users complain about slow speed out to Internet.  If we force traffic to AT&T via ASA, speed issue goes away.

We don't see any issue on 2951 router in terms of CPU or memory util.

WHat can cause slow speed despite the fact that router resources are not maxed out and Comcast circuit has 150% more capacity than AT&T?

Thanks,
Paresh

[jigardavenm]

Is there any CIR configuration exist on your WAN port?

could you paste your 2951 ISR configuration for our further review to help you?

Thanks.

jd

[pkpatel]

Hello Jigar - there is o CIR on router.  I will post config later.

Thanks,
Paresh

[paolo bevilacqua]

You may have a faulty config on the 2951.

[pkpatel]

Hello Paolo,

I dont believe that the config might be at fault here but will post it later tonight.

Thanks,

Paresh

[Joseph W. Doherty]

Disclaimer

The  Author of this posting offers the information contained within this  posting without consideration and with the reader's understanding that  there's no implied or expressed suitability or fitness for any purpose.  Information provided is for informational purposes only and should not  be construed as rendering professional advice of any kind. Usage of this  posting's information is solely at reader's own risk.

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Posting

Normally Comcast modems offer asymmetrical bandwidth, i.e. something like 50 down and 10 up.  Do you know what your down/up values are? Do you shape for up bandwidth?  Is the AT&T 20 symmetrical?

[mavespig]

I agree with Joseph, broadband cable offers on the market are 99% of the time asymmetric.

If your Comcast subscription is Comcast Extreme, it's 50 DS and 12 US.

Perhaps you can double check both links by doing a speed test (e.g. speedtest.net)

Marco

[pkpatel]

Hello Joseph and Marco - you guys are correct.  Comcast is 50 Down/10 Up.  AT&T is 20/20.  The problem reported however is during course of normal Internet browsing.

[Joseph W. Doherty]

Disclaimer

The   Author of this posting offers the information contained within this   posting without consideration and with the reader's understanding that   there's no implied or expressed suitability or fitness for any purpose.   Information provided is for informational purposes only and should not   be construed as rendering professional advice of any kind. Usage of  this  posting's information is solely at reader's own risk.

Liability Disclaimer

In   no event shall Author be liable for any damages whatsoever (including,   without limitation, damages for loss of use, data or profit) arising  out  of the use or inability to use the posting's information even if  Author  has been advised of the possibility of such damage.

Posting

On the Comcast side, is this a Business Class connection?  If residential (or commercial?), bandwidth is shared to your modem and there are special traffic markers if you use a lots of bandwidth.  I.e. "up to" is often the adjective with cable modems.  On AT&T your 20 Mbps might be guaranteed.  This might account for your difference.  One way to tell is graph bandwidth usage when using the Comcast modem and see what it shows "when it's slow".

Could be other issues too, which is why I asked about traffic shaping for upstream.