On 8/21/2014 8:47 AM, Brian Trammell wrote:
hi Joe, all,

okay, I'm convinced for passive FTP (and s/FTP/active-mode FTP/g in
myprevious message).

Now the problem would remain -- how, in an interfaceless
environment, can the tcpinc machinery tell passive from active FTP in
advance?

Why would it want/need to, any more than IPsec over UDP would?

However, a SYN issued from port 20 would tell you it's active.

One possible approach here would be to detect a failed
active FTP transaction, then rely on the application to try again and
remember to disable itself for the second attempt (kind of like
Valery's option 4, but with fallback).

FTP users already know to try passive mode FTP, AFAICT.

Of course this leads to the type of implementation complexity I was
hoping to avoid through deprecation. I still think any pressure we can
exert to speed active-mode FTP's retirement is effort better spent than
effort building fiddly bits into tcpinc (Valery's option 6) for this
corner case.

There's no need tor retire anything. You can just recommend that the default is to use passive mode if you want, though.

Joe


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