Re: Comcast throttling?

["Justin M. Streiner" <streiner () cluebyfour org>]

On Fri, 31 Oct 2014, Mark Price wrote:

> Similar to another thread on the list today, I'm troubleshooting a problem
> for a customer on Comcast business fiber.
>
> Downloading a file from one of our web servers is very slow (~15KByte/sec).
> mtr looks clean in both directions.  I added an IP address on the same
> server from a different class C on our network, and downloads form this new
> IP are fast (2MByte/sec).
>
> Tracerouting from server to client is the same using both source IPs.  But,
> one IP consistently has the very slow speeds that the other does not.
> Changing our outbound path between different upstreams does not make a
> difference.
>
> It certainly feels like Comcast is throttling one of our IP ranges.  Could
> someone at Comcast please contact me off-list for details?

That's possible, but while a traceroute can help shed some light on 
certain performance problems, this doesn't seem like one where a 
traceroute will help very much.  The slow traceroute hops are more likely 
due to other factors (ICMP rate limiting / control plane policing / etc), 
rather than a direct indicator of Comcast shaping / throttling your 
traffic.

As others have indicated, doing a packet capture of a transfer session 
that shows the behavior you noted is likely to be a lot more telling than 
a traceroute.

jms