[atlas] RIPE Atlas SMTP Measurement

Hi Michel,

 >Are we monitoring the Internet or monitoring a service using the proposed SMTP measurement?
First of all, we are monitoring the service of a specific target. Same as http or ntp measurements, just another protocol. But we also monitor the Internet. Using an SMTP measurement, we could identify censorship or discover Man-in-the-middle attacks (downgrade attack by suppressing the STARTTLS command).

 >Can we achieve the first 2 items of this measurement by doing a TCP traceroute on port 25?
I would say no. Using TCP Traceroute, you can may check for reachability/responsiveness of the host, but not the actual service (smtp).

 >Does the SSL measurement cover the intended use cases?
I would say no. Correct me if am am wrong. Usually (for example HTTPS or LDAPS) the SSL/TLS encryption starts right after the TCP 3-way Handshake was successfull. For SMTP, that doesn't work. That's because regular SMTP communication starts first, so both sides can negotiate if SSL/TLS encryption is possible (via Enhanced SMTP Status Codes). However, as far as i know, OpenSSL _does_ support SMTP and STARTTLS. So you could probably modify the existing SSL measurement.

Keep in mind that there's also MTA-STS and DANE, which are really enhancing SMTPs security. A dedicated SMTP measurement would be a good thing.

BR,
Simon



On 23.09.22 16:04, Michel Stam wrote:
> Hi everyone,
>
> Great that this request sparked a good discussion on the merits of a measurement, as well as its potential impact on servers around the world. Good to see this!
>
> So I’m going to do a quick recap here, hoping that I capture the intent and the concerns correctly. Please correct me if I err.
>
> The intent of the measurement would be to validate whether an SMTP server is:
>
>   * reachable
>   * responsive
>   * capable of secured transmissions
>
>
> The concern is that such a check would trigger one of a variety of anti spam measures in place around the world, and/or cause undue traffic to SMTP server operators.
>
> With this in mind, I am wondering:
>
>   * Are we monitoring the Internet or monitoring a service using the proposed SMTP measurement?
>   * Can we achieve the first 2 items of this measurement by doing a TCP traceroute on port 25?
>   * Does the SSL measurement cover the intended use cases?
>       o  Is it worth exploring STARTTLS support as an extension and what would the implications be?
>
>
> Have a good weekend!
>
> Best regards,
>
> Michel
>
>> On 21 Sep 2022, at 00:11, Avamander <avamander at gmail.com> wrote:
>>
>> > Making arguments based upon extreme cases, assumptions, or potential-for-collateral-damage is not scientific. "I know one that even [...]" Anecdotal  evidence isn't scientific.
>>
>> From the perspective of your previous sentences that's kinda humorous. "To avoid unnecessary costs incurred from disruption of service, excessive traffic, annoyances using up *my* time, and countless other reasonable rationale from *my* point of view." Because sure, a few (hypothetical RIPE probe) connections are exactly that, zero exaggeration, right?
>>
>> In the end such fail2ban-fueled (or similar) behaviour I initially addressed, is exactly a non-scientific extreme-case assumption-based approach. There are better and even more standard ways.
>>
>> Crutch solutions out in the wild shouldn't be a showstopper for measuring the ecosystem. (That is already quite neglected)
>>
>> > What _objective_ risk/benefit analysis are you basing your opinions upon?
>>
>> And you? What's the implication here about systems being as trigger-happy as previously described?
>>
>> Because sure, at some point rate limits make total sense, but certainly not at the point where it would ban any potential RIPE probes.
>>
>> >  Are you a systems administrator?
>>
>> Let's not get into such measuring contests, even if it is the RIPE Atlas mailing list.
>>
>> On Tue, Sep 20, 2022 at 11:42 PM Paul Theodoropoulos via ripe-atlas <ripe-atlas at ripe.net> wrote:
>>
>>     On 9/20/2022 10:45 AM, Avamander wrote:
>>>     Great to hear it works for you, but the potential unfortunate collateral from such a blanket action is not really RIPE Atlas' problem. There are more fine-grained methods against bruteforce attempts and open relay probes, than triggering on a few connections.
>>     What _objective_ risk/benefit analysis are you basing your opinions upon? Are you a systems administrator? My responsibility is to avoid unnecessary costs incurred from disruption of service, excessive traffic, annoyances using up *my* time, and countless other reasonable rationale from *my* point of view.
>>
>>     You suggest that it is "not really RIPE Atlas' problem". That's very true. And it is not really my problem if I bounce yoinky, pointless probes of my server, and ruthlessly block them from contacting my server ever again. My server, my choice, my wallet, nobody's business but my own.
>>>     Some webmasters ban IP's for simply visiting a domain, I know one that even dispatches an email to your ISP's abuse@ address upon visit. Should RIPE Atlas probes then not probe any HTTP servers? The answer is obviously no, they shouldn't care.
>>     Making arguments based upon extreme cases, assumptions, or potential-for-collateral-damage is not scientific. "I know one that even [...]" Anecdotal  evidence isn't scientific.
>>
>>     Note, I run a probe myself. I don't block any RIPE Atlas traffic on my separate servers hosted on AWS, Oracle, and GCE.
>>
>>     -- 
>>     Paul Theodoropoulos
>>     anastrophe.com <https://www.anastrophe.com/>
>>     -- 
>>     ripe-atlas mailing list
>>     ripe-atlas at ripe.net
>>     https://mailman.ripe.net/
>>
>> -- 
>> ripe-atlas mailing list
>> ripe-atlas at ripe.net
>> https://mailman.ripe.net/
>
>
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