Seeking Comcast Contact: need to troubleshoot packet loss and/or asymmetric routing issue between Comcast & Onvoy

Durand, Alain Alain_Durand at
Thu Aug 2 13:43:35 UTC 2007

I've forwarded your message to the appropriate team within Comcast.

  - Alain. 

> -----Original Message-----
> From: owner-nanog at [mailto:owner-nanog at] On 
> Behalf Of Craig D. Rice
> Sent: Thursday, August 02, 2007 9:30 AM
> To: nanog at
> Subject: Seeking Comcast Contact: need to troubleshoot packet 
> loss and/or asymmetric routing issue between Comcast & Onvoy
> For four months dozens of our users who are Comcast 
> subscribers have had difficulty reaching St. Olaf College's 
> and Carleton College's network services.
> We have worked through everything we can think of with our 
> Onvoy (regional
> ISP) network engineers. We have isolated the problem a couple 
> of Comcast's IP subnets, but need a contact within Comcast to 
> further troubleshoot.
> The behavior in a nutshell:
> --
> User A on Comcast Subnet B browses to (http or 
> https, other web sites on-site and behave the 
> same). Our access_log shows an initial "GET /" of our 
> homepage, then very slow (if any) subsequent requests (for 
> our stylesheet or homepage images). Ping's look fine; 
> traceroute's look as reasonable. Telnet's to port 80 and 
> other services do seem to respond, albeit very slowly.
> User A has the same problem with access but can 
> access everything else (including other Onvoy customers) 
> without any trouble whatsoever.
> If User A then removes his Linksys router and connects his 
> computer directly to the cable modem, he acquires an IP 
> address in Comcast Subnet C. Then, everything works fine, 
> including access to and He 
> puts the Linksys router back in (which still has the IP 
> address in Comcast Subnet B), and the problem returns.
> The problem IP subnets are completely consistent.
>      Known WORKING IP Subnets:, 24.x Known 
> NON-WORKING IP Subnets: 71.x, 73.x
> --
> We have already attempted the usual troubleshooting and have 
> eliminated user problems, computer problems, server problems, 
> cable modem problems, and Linksys router problems. 
> Traceroutes have been somewhat inconclusive since Onvoy 
> blocks ICMP within its network.
> So, why just St. Olaf and Carleton services? We are on a 
> shared physical link from Onvoy, though on different VLANs. 
> Onvoy has verified everything they can (routing, packet loss, 
> etc.) between them and us, and I'm not sure what additional 
> questions I can ask of them to test. Suggestions?
> Maybe Comcast has a broken transparent proxy on part(s) of 
> their network? 
> But they have told us they have nothing like this anywhere on 
> their network.
> Maybe there is some asymmetric routing somewhere, though all 
> the investigation there has come up empty.
> A third possibility is some kind of packet loss, but there is 
> little if any evidence of that.
> So, we are really at a loss and seek any suggestions you all 
> might have. And a contact in Comcast network engineering 
> would be especially useful to continue our troubleshooting.
> With thanks,
> Craig
> -- 
> Craig D. Rice                  Associate Director of 
> Information Systems
> cdr at                Information and Instructional 
> Technologies
> +1 507 786-3631                                         St. 
> Olaf College
> +1 507 786-3096 FAX                                 1510 St. 
> Olaf Avenue
>         Northfield, MN  
> 55057-1097  USA

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