Re: Sendmail Five Second Greeting Delay



On 4/2/10 8:33 AM, David Allen wrote:

Secondly, it seems the cause of the OP's problem was a delay associated
with an IDENT query. Specificially

confTO_IDENT Timeout.ident [5s] The timeout waiting for a
response to an IDENT query.

If he had local DNS configured, there would be no query, and therefore no
issue, but setting the timeout to 0 seconds using

define(`confTO_IDENT', 0s)

does remove the delay, but not the underlying problem.

You sure? IDENT has nothing to do with DNS, and I don't know of any program that does an IDENT query solely if DNS data is not available. I can't see why that would make any sense.

What is most likely the OP's root problem is that he's sending e-mail from a machine that's on the other side of a firewall that blocks IDENT traffic but doesn't actively reject it. So sendmail has to sit around and wait for the query to time out.

This is why there's a school of thought that even if your default for firewall configuration is to quietly drop unwanted packets, IDENT is a protocol that you should actively reject. It makes things move along more quickly.


Put another way, I'm wondering why IDENT queries are made? My knowledge
of that protocol is superficial, but my understanding is that running an
identity service is widely considered a security problem. FreeBSD doesn't
run identd by default, for example, but it's possible that some Linux
distros do. The Wikipedia article suggests "It's an IRC thing", but that
doesn't address the default sendmail behavior.

Things can make more sense when you realize that TCP/IP networks have changed over the years. Long ago, when dinosaurs roamed the earth, and timesharing servers were big things with professional admins and lots of users, it could be helpful to know that if you got an irritating connection from the Math Dept. server using source port X, and IDENT said the owner of the process that was using port X was a user called Jimbob, that you could go to the admin of that server and tell him to slap Jimbob upside the head. After all, if his IDENT server had been subverted, he would have mentioned it when you had a beer with him last night.

These days, when so much traffic comes from individual workstations where the user can frequently arrange for an IDENT server to return any fool information they want, if they have it running at all, the value added is much less.

Do remember that some of these things date from back when Linus was still in diapers (well, actually, he was about 15 when the earliest RFC with the genesis of IDENT was published), so trying to figure out why they make sense based solely on what Linux does can be futile. ;-)

--

--Jon Radel
jon@xxxxxxxxx



Relevant Pages

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