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Port Squatting


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Port Squatting, illustration

back to top  Dear KV

A few years ago you upbraided some developers for not following the correct process when requesting a reserved network port from IETF (Internet Engineering Task Force). While I get that squatting a used port is poor practice, I wonder if you, yourself, have ever tried to get IETF to allocate a port. We recently went through this with a new protocol on an open source project, and it was a nontrivial and frustrating exercise. While I would not encourage your readers to squat ports, I can see why they might just look for unallocated ports on their own and simply start using those, with the expectation that if their protocols proved popular, they would be granted the allocations later.

Frankly Frustrated

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Dear Frankly

Funny you should ask this question at this point. This summer I, too, requested not one, but two ports for a service I had been working on (Conductor: https://github.com/gvnn3/conductor). I have always been annoyed there is not a simple, distributed, automation system for orchestrating network tests, so I sat down and wrote one. The easiest way to implement the system was to have two reserved portsone for the conductor and one for the playersso that each could contact the others independently without have to pass ephemeral qports around after they were allocated by the operating system during process startup.

Simple enough, you might think. It is not actually IETF to which one appliesit is IANA (Internet Assigned Numbers Authority). It has a form you fill out on its Web site, detailing your request (https://www.iana.org/form/ports-services), which asks fairly reasonable questions about who you are, which transport protocol your protocol uses (UDP, TCP, SCTP, and so forth), and how the protocol is used. Because there are only 16 bits in the port field for UDP, TCP, and SCTP, space is limited, so you can see why IANA would want to be careful in its port allocations. Looking over the current assignments, we can see that nearly 10% of the space has already been allocated for TCP, with more than 6,100 assigned ports for TCP.

I submitted my request for a pair of ports over TCP and SCTP on July 7. I applied for both because it made sense to address both of the currently available, reliable, transport protocols. As I write this, it is September 6, and I am assured that by September 8 I will have a single port assigned; I finally got the port assignment on September 18. Let's look at the process.

Once you submit your port request, it goes into a ticketing system, RT (request tracker), which is looked after by someone whom I will call a secretary. The secretary seems to do some form of triage on the ticket and then passes it along to someone else. For the past two months, the secretary asked clarifying questions about the use of the two port numbers. It was plain from the interaction that the secretary did not have any significant networking knowledge but acted as a pass-through for the experts reviewing the case. As might be expected with any sort of overly bureaucratic process and with this form of telephone game, information was often lost or duplicated, requiring me to explain at length how I was going to use the ports. In the end, I was contacted by an expertsomeone actually knowledgeable about networking technologyand we agreed the service could be built with one port number. I say "agreed," but mostly I relented, because I was going to do this right, even if I put my fist through a whiteboardand let me tell you, I came very close to doing just that.


Systems administrators are often the busiest and most harried people at any IT site.


This brings me to a few statistics about the assigned numbers. Many of the assignments for TCP are not for a single port, but for multiple ports, meaning the number of services is fewer than the 6,100-plus assigned ports. Not only are there many services with more than one port, but it would also seem that dead assignments are not garbage collected, which means that although only 10% of the space is used, there is no way to reclaim ports when protocols or the companies that created them die. Looking through the list of assigned ports is a walk down the memory lane of failed companies.

All of which is not to encourage people to squat numbers, but it is pretty clear that IANA could do some work to streamline the process, as well as reclaim some of the used space. The biggest problem actually exists in the first 1,024 ports, which most operating systems consider to be "system" ports. A system port is usable only by a service running as root, and this is considered privileged. The domain name system, for example, runs on port 53. It is in this low space that IANA needs to get its collective act together and kill off a few services. Although I am sure all of you are using port 222Berkeley rshd with SPX autheach and every day.

KV

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Dear KV

I have been revising the logging output for a large project, and it seems every time I propose a change, our systems admins start screaming at me to revert what I have done. They seem to think the format of our log output was set in stone at version 1 of the product and that I should not actually touch anything, even though the productnow at version 3does quite a bit more than it did in version 1. I understand that changing the output means they will have to change some scripts, but I cannot help it if there are new features that need to log new information.

Log Rolled

* Dear Logged

I do not know if you know this, but systems administrators are simply lazy layabouts who spend all their days slacking off work, putting their feet up the desk, and sipping single malts while the boss is not looking. Actuallyin point of factsystems administrators are often the busiest and most harried people at any IT site, and they are the people responsible for knowing if all the systems are UP or DOWN. If you capriciously change the logging output on their systems, the tools they have lovingly crafted to track the performance of your system will indicate things are DOWN when they are probably not, and this will result in a lot of screaming. I like coding in a quiet environment; I do not like screaming so do not make the sysadmins scream.

There are good ways and bad ways to update log output. Inserting a new column at the beginning of each line, thereby throwing off all the following columns, is an incredibly bad way of updating a log file. In fact, the first columns of any log output should always be the date and timewith seconds. Using the date for the first column makes writing analysis scripts far easier. Just like extending a programming API, unless you have a very good reason, you should always add new information at the end of the line. Extra columns are the easiest to ignore and the least likely to cause the sysadmin tools to go nutty. That therefore reduces the amount and volume of screaming in the office (see my previous mention of offices and quiet).

Another less offensive way of updating log output is to add whole new lines of information, so that scripts can look at the old lines correctly and, for as long as possible, ignore the new information. Allowing the script authors some time to update their scripts is just the kind of thing you would want to encourage.

Finally, you might simply add an option to the program to output the old log format so the people running your software have time, again, to update their scripts, or, perhaps, they really do not need the new information and would like the chance to use your system without touching their pristine and beautiful scripts. Think first before forcing new information on the user.

KV

q stamp of ACM QueueRelated articles
on queue.acm.org

Error Messages: What's the Problem?
Paul P. Maglio, Eser Kandogan
http://queue.acm.org/detail.cfm?id=1036499

Collaboration in System Administration
Eben M. Haber, Eser Kandogan, Paul Maglio
http://queue.acm.org/detail.cfm?id=1898149

Advances and Challenges in Log Analysis
Adam Oliner, Archana Ganapathi, Wei Xu
http://queue.acm.org/detail.cfm?id=2082137

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Author

George V. Neville-Neil (kv@acm.org) is the proprietor of Neville-Neil Consulting and co-chair of the ACM Queue editorial board. He works on networking and operating systems code for fun and profit, teaches courses on various programming-related subjects, and encourages your comments, quips, and code snips pertaining to his Communications column.


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The Digital Library is published by the Association for Computing Machinery. Copyright © 2014 ACM, Inc.


 

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