Comcast Ethernet Feed

Randy randy_94108 at
Thu Mar 29 20:49:48 CDT 2012

--- On Thu, 3/29/12, Brian R. Watters <brwatters at> wrote:

> From: Brian R. Watters <brwatters at>
> Subject: Comcast Ethernet Feed
> To: "NANOG list" <nanog at>
> Date: Thursday, March 29, 2012, 5:36 PM
> We are about to accept a 20MEG
> Ethernet feed via Comcast and their fiber plant as well as a
> BGP feed across the same link.
> I have a space GIGE interface on a 7206VXR and would like to
> know best practice for deploying for optimal performance
> across this interface.
> Any ideas and or direction would be extremely helpful as we
> are seeing some real issues such as.
> Direct connect (without BGP) to the CPE from Comcast (Fiber
> to Ethernet) via a laptop gives the level of performance we
> would expect, However as soon as we terminate to our router
> via the GIGE which is set to 100MB full duplex and all flow
> control turned off (Negotiation auto) per Comcast and
> connect up via a 100MB fast Ethernet interface directly
> connected we get a fraction of the speed when direct
> connected.
> Ideas?

A couple of questions - 

1) What flavor of NPE are you using?
2) Is the GigE interface on the NPE-G1/G2  OR is this a PA?
3) Is the FaE ethernet interface that you appear to be connecting your laptop to, on a separate PA in chassis?
4) Have you verified you that "bandwidth-points" have not been exceeded for bus-1 and/or 2: slots 1,3,5 for bus1 and 2,4,6; also 0(if I/O controller is present. It is 600 points for bus1 and 600 for bus2.
(A sh ver will provice the info)

You can google:
"Cisco 7200 Series Port Adapter Hardware Configuration Guidelines"
for additional info.


Have you *hard-coded* speed and duplex on any of you eth ints? Please don't!

Let both ints auto-negotiate speed&duplex.

after having done so, post the output of:

sh int gi x/y and sh int fa x/y

(hardcoding speed/duplex is sometimes required when dealing with brain-dead CPE. I have also seen other flavors of brain-dead CPE that *only* work when speed/duplex are set to auto)


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