Subj : IPv6 only node?
To   : Tommi Koivula
From : Michiel van der Vlist
Date : Wed Apr 26 2017 15:22:43

Hello Tommi,

On Wednesday April 26 2017 11:09, you wrote to me:

 MV>> Some mailers like Frontdoor and Intermail have the option of user
 MV>> configurable flags.

 TK> Every mailer could be configured per node. But my point was if there
 TK> is a mailer that can understand the INO4 flag and try connection only
 TK> by IPv6. Without any custom configuration.

Hmmm... I think you misunderstand the reasoning behind the INO4 flag. It is not meant (although it /may/ probably be used for that) to let mailers connect via IPv6 only. IPv6 capable mailetrs will not have to be told explicitly to connect only via IPv6 when only an IPv6 address is available. They will do that all by themselves.

No, it is different. Strictly speaking -the INO4 flag is about IPv4. It means that the node in question does NOT have incoming IPv4 capability. It so happens that this implies IPv6 only, but that is only because presently we only have IPv4 and IPv6. That may change with te coming of IPv7...

Anyway, the main idea behind the INO4 flag is to prevent mailers from fruitlessly trying to connect via an IPv4 only connection.

With intermail for example I could use:

Hold INO4, !CM, 300

To tell it to put mail on hold for nodes carrying the INO4 flag, not carrying the CM flag and a maximum speed of 300. InterMail knows nothing about IPv4 or IPv6 but it can be told to recognise the INO4 flag and act upon it.

Or I could tell it the following.

Host-Route INO4.

I think that speaks for itself.

 TK> I agree with Alexey, if there is ipv6 address in the nodelist, the
 TK> INO4 flag is useless.

You are only looking at IPv6 capable mailers in your considerations. But what about Netmail routers/trackers and other software? Netmail routers do not know about IPv6, They do not recognsies IPv6 addresess. But they can be trained to act on the INO4 flag. I already menationed "Host-Route INO4". That actaully is a router directive, not a mailer directive.

OT-Ttrack can act on nodelist flags. From the doc:

         /IfFlags="data;data;...;data"

                        The command (e.g. ATTR or SENDER) will only apply
                        on messages, where the DESTINATION address matches
                        "data" in the current nodelist(s). (Note: "data" OR
                        "data" OR "data"!!!)
                        A useful example for this: You want to route all
                        messages but those addressed to nodes with either
                        the ENC of the NEC flag. If a message is destined
                        to an ENC *or* NEC node, you want to send it
                        directly.

This would apply to the INO4 flag as well.

Think out of the box...

 TK> 2:221/10 is up now and binkp.net resolves it ok.

Using binkp.net by the mailer comes down to feeding it a url instead of a literal IPv6 address. The mailer is poresented with the url fx.ny.zz.binkp.net. The mailer does not know in advance that only an IPv6 address will retuern. Just the same as with fido6.ddutch.nl. So if the INO4 flag is useful when the nodelist contains a url, it is also useful for those using binkp.net and a literal address in the nodelist.


Cheers, Michiel

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