Comcast Ethernet Feed

Brielle Bruns bruns at
Thu Mar 29 20:06:59 CDT 2012

On 3/29/12 6:53 PM, Jon Lewis wrote:
> On Thu, 29 Mar 2012, Brielle Bruns wrote:
>> From my own experience here with our 7200s, some of the PA based
>> 100BaseT interfaces (ie: not on the IO module) can not negotiate
>> 100-full, but rather only half.  This leaves one end diff then the
>> other and creates issues with performance.  Try forcing both the
>> laptop and router to 100-full and see if it helps.
> Those interfaces don't to auto-negotiation at all.  That's why they
> default to 100 half.  OP said they were using a Gig interface though.
> Maybe a copper 10/100/1000 port on an NPE-G<1|2>?  I haven't used those,
> but I'd bet they support auto-negotiation.  1000baseT requires it.

I'm pretty sure the PA-FE-TX boards can do auto neg, just not 100 full 
(just tested with a 7507 with a VIP4 w a PA-FE-TX and a cheap 10BT hub - 
my 7206VXR is not powered up ATM).

Believe it has something to do with the DEC ethernet chip they use (I 
have an older desktop that just happens to have the same DEC chipset 
that those do and has exactly the same problem).

Based on what he said, I read his setup as having a G1 or G2 NPE, using 
the on-NPE gig to hook to comcast, and a PA-FE-TX in one of the PA slots.

At least, that's how it sounded to me - why else use 100BaseT on a gige 
as most laptops and desktops in the past... 4-5 years or so have onboard 

Brielle Bruns
The Summit Open Source Development Group    /

More information about the NANOG mailing list