Re: Ports for testing UDP
- From: jguthrie@xxxxxxxxxxxxx
- Date: Wed, 21 Dec 2005 23:25:21 -0600
Sam of California <samuel@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
> <jguthrie@xxxxxxxxxxxxx> wrote in message
> news:5ipb73-66j.ln1@xxxxxxxxxxxxxxxxxxxxxxxxx
>>
>> I think that your question is confused and, therefore, confusing.
> My question might be confusing to you, but I don't understand how a question
> can be confused. A question asks for information, it does not get
> information. Also, a question does not have any intellignece to get
> confused.
I mean that the questioner appears to be confused. In my opinion, your
question lacks precision and polish, and it is, therefore, difficult to
answer. As evidence supporting my conclusion I offer this: I tried to
answer it by guessing what you likely meant to ask but all my answers
did was make you mad. Nobody else seems to have taken a stab at
answering your question, so I conclude that I'm not alone in thinking
that the question is not particularly well phrased.
> I think you are saying that my question is confused because you are being
> excessively critical.
No, I'm trying to give a reason why nobody is attempting to answer your
question. If you ask a better question, then you'll likely get more and
better answers. It's been thirty years since I figured out the quality
of answer you get depends strongly on the quality of the question that
you ask (and I started to ask better questions when I got answers that
didn't give me the answers that I wanted.)
The question that you asked (as I recall "how do I know what ports are
going to be used") didn't appear to make sense because there is no way
to answer that question. People are free to have their programs listen
on whatever ports they want and it is not, in general, possible to know
which ports are going to be used. A variety of techniques are used to
deal with the possibility of collisions, but the most common one is
configurability. Heck, even programs that use well-known ports are
usually made configurable because it allows greater flexibilty of
operation.
Perhaps you're asking how to determine what programs might be used.
That's still a little broad to give a reasonable answer to, but
answering that question is why I talked about netstat and looking for
errors at startup. Most of the computers I set up services on run those
services from the time they're started until the time they're shut down
so looking at netstat will tell me all the ports that it's ever going to
listen on unless I run a program that listens on a different one.
Perhaps you're asking about how to have a port assigned to you by IANA.
If that's the case, then Googling is probably what you want to do.
Search for "assigned numbers" and "RFC" and see what it gets you.
However, you'll likely find that a tough row to hoe. So to speak.
Perhaps not, I've not attempted to get a port assigned to a protocol so
I don't have a clue what the process is.
In any case, I still don't understand your question. I thought I made
that clear in my intial response. Apparently, I did not so I will be
more explicit: I do not understand your question. Instead of
berating me for criticism, please clarify: What do you hope this
technique will be able to accomplish? Can you give examples of what
you're hoping to avoid? Maybe that will help me understand you.
> My question is valid, since I have written a program for which the question
> is relevant to. You are assuming I don't know enough about UDP to know how
> ports are used by UDP. You should not be so quick to assume such things and
> criticize accordingly.
I'm sorry that my manner of speaking offended you. I'm not criticizing,
but asking for clarification. Perhaps if you were to go into more
detail I would understand. Port collisions are bad, but they aren't
very likely. I've done a half-dozen or so UDP-based protocols and have
never had any problems in my applications by simply using a port in the
nonprivileged range that didn't appear in /etc/services and which didn't
show up in a netstat on a server running a lot of services.
>> When I'm interested in seeing what ports are known to be used, and for
>> that, I normally look in /etc/services on one of my computers.
> Huh?
The "that" should be a "what". That's a typo. Is this any clearer?
When I'm interested in seeing what ports are known to be used, and for
what, I normally look in /etc/services on one of my computers.
If you know what the /etc/services file is for, I'm sorry, but I've got
to assume you don't know what it is because that seems likely. (If you
had said something like "Huh? That sentence doesn't parse" or "Huh? I
don't know why you would look in /etc/services" or "Huh? What's an
/etc/services file?" I would know how to change what I said to make it
more clear.) If you do Windows, then perhaps it would help to say it's
a Unix-y thing. Although your apparent familiary with netstat implies
that you're likely not a Windows only user and, in any case, I don't
think that would be what your question is because I think that
mentioning a file in that context would at least imply some sort of
Unix-y thing.
Anyway, the /etc/services file on my computers lists a bunch of ports,
both UDP and TCP, and what they're commonly used for. If it's not
listed in /etc/services, a particular UDP port is not likely to be used
for much of anything. In particular, I would expect every UDP port
listed in various standards documents to be in /etc/services, although
I wouldn't be surprised if that expectation proves false. I sometimes
have to look some of the ports I see in my firewall logs up in various
places because they aren't listed in /etc/services.
>> My
>> experience suggests that ports above 8000 are rarely used by much of
>> anything and UDP isn't used much at all.
> Isn't that what I said?
Maybe. If so, then you can consider that confirmation.
--
Jonathan Guthrie (jguthrie@xxxxxxxxxxxxx)
Sto pro veritate
.
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