Thank you, Comcast.

David Bass davidbass570 at
Fri Feb 26 15:54:26 UTC 2016

I agree with this...from a customer perspective.  I've seen ISPs block other traffic as well...even on "business" accounts, and break their customers networks.  

It's the Internet not a private network...

I've never been a typical user though...maybe one of the "dozen" Mike refers to that runs a email server, web server, dns server, etc, etc, etc out of their house. 

> On Feb 26, 2016, at 9:31 AM, Keith Medcalf <kmedcalf at> wrote:
> ISP's should block nothing, to or from the customer, unless they make it clear *before* selling the service (and include it in the Terms and Conditions of Service Contract), that they are not selling an Internet connection but are selling a partially functional Internet connection (or a limited Internet Service), and specifying exactly what the built-in deficiencies are.
> Deficiencies may include:
>  port/protocol blockage toward the customer (destination blocks)
>  port/protocol blockage toward the internet (source blocks)
>  DNS diddling (filtering of responses, NXDOMAIN redirection/wildcards, etc)
>  Traffic Shaping/Policing/Congestion policies, inbound and outbound
> Some ISPs are good at this and provide opt-in/out methods for at least the first three on the list.  Others not so much.
>> -----Original Message-----
>> From: NANOG [mailto:nanog-bounces at] On Behalf Of Maxwell Cole
>> Sent: Friday, 26 February, 2016 07:19
>> To: Mikael Abrahamsson
>> Cc: NANOG list
>> Subject: Re: Thank you, Comcast.
>> I agree,
>> At the very least things like SNMP/NTP should be blocked. I mean how many
>> people actually run a legit NTP server out of their home? Dozens? And the
>> people who run SNMP devices with the default/common communities aren’t the
>> ones using it.
>> If the argument is that you need a Business class account to run a mail
>> server then I have no problem extending that to DNS servers also.
>> Cheers,
>> Max
>>>> On Feb 26, 2016, at 8:55 AM, Mikael Abrahamsson <swmike at>
>>> wrote:
>>>> On Fri, 26 Feb 2016, Nick Hilliard wrote:
>>>> Traffic from dns-spoofing attacks generally has src port = 53 and dst
>> port = random.  If you block packets with udp src port=53 towards
>> customers, you will also block legitimate return traffic if the customers
>> run their own DNS servers or use opendns / google dns / etc.
>>> Sure, it's a very interesting discussion what ports should be blocked or
>> not.
>>> This mentions on page 3.1, TCP(UDP)/25,135,139 and 445. They've been
>> blocked for a very long time to fix some issues, even though there is
>> legitimate use for these ports.
>>> So if you're blocking these ports, it seems like a small step to block
>> UDP/TCP/53 towards customers as well. I can't come up with an argument
>> that makes sense to block TCP/25 and then not block port UDP/TCP/53 as
>> well. If you're protecting the Internet from your customers
>> misconfiguraiton by blocking port 25 and the MS ports, why not 53 as well?
>>> This is a slippery slope of course, and judgement calls are not easy to
>> make.
>>> --
>>> Mikael Abrahamsson    email: swmike at

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