New Outage Hits Comcast Subscribers

Thu Apr 14 19:03:03 UTC 2005

Do you understand anycast? Do you understand how different operating 
systems react to failures of configured dns servers?

You really need to look into anycast and see why it is used. Perhaps 
the comcast people are as naive as you about dns... Check out:
http://www.net.cmu.edu/pres/anycast/

or my favorite: http://www.net.cmu.edu/pres/lisa03/

This excellent presentation will help you with your understanding:

"In configuring multiple hosts to respond to the same address, 
stateless protocols such as DNS can be easily scaled. Servers can be 
located in closer proximity to clients, providing faster responses to 
queries. In the event of a single host failure, routes can quickly be 
withdrawn and servers in other locations handle the request traffic, 
all without any changes to client configurations.

  Recursive DNS clients built into many of today's operating systems 
deal rather poorly with a failure of their primary recursive server. Of 
eight operating systems evaluated in a recent survey, seven kept no 
history of failed servers, trying each DNS query against the first 
server and waiting for a response before moving to secondary servers. 
Using anycast, service is maintained even in the face of a single or 
multiple host failure. This substantially reduces resolution delays due 
to server failure."

Peter Hill

On Apr 14, 2005, at 11:24 AM, Daniel Senie wrote:

>
> At 02:00 PM 4/14/2005, Peter John Hill wrote:
>
>> I have completely given up on relying on Comcast for dns service... 
>> For now I will continue to use them for "transit"
>>
>> If they are unwilling to implement anycast dns then I cannot trust 
>> them...
>
> It's unclear why anycast would be required. Most or all of their 
> customers use DHCP to obtain address information, including DNS 
> information. It would be just as reasonable for them to install a few 
> small DNS servers along-side the router at the cable head-end at every 
> town. Now it might be simpler for them to manage if they placed those 
> same servers but used Anycast, but the effect should be the same.
>
> The point is, anycast is not the issue. Reliable service is the issue. 
> DNS isn't their only issue, of course (that they're single-homed to 
> AT&T adds to their unreliability, not that they can fix that at 
> present).
>
> Dan
>
>
>