The Book of PF, 4th Edition: It's Here, It's Real

In case you missed it earlier,

The Book of PF, 4th Edition: It's Here, It's Real nxdomain.no/~peter/its_r...

And I will have copies with me to upcoming events #openbsd #freebsd #bsd #pf #packetfilter #bookofpf #4thedition #asiabsdcon #bsdcan #eurobsdcon

The Book of PF, 4th Edition: It's Here, It's Real

In case you missed it earlier,

The Book of PF, 4th Edition: It's Here, It's Real https://nxdomain.no/~peter/its_real_its_here.html

And I will have copies with me to upcoming events #openbsd #freebsd #bsd #pf #packetfilter #bookofpf #4thedition #asiabsdcon #bsdcan #eurobsdcon

The Book of PF, 4th Edition: It's Here, It's Real

The Book of PF, 4th Edition: It's Here, It's Real nxdomain.no/~peter/its_r... - now that I have physical copies, I'll bring some to the upcoming conferences such as #asiabsdcon #bsdcan #eurobsdcon #freebsd #openbsd #pf #packetfilter #networking #networktrickery #freesoftware #libresoftware #bookofpf

Original post on mastodon.social

The Book of PF, 4th Edition: It's Here, It's Real https://nxdomain.no/~peter/its_real_its_here.html - now that I have physical copies, I'll bring some to the upcoming conferences such as #asiabsdcon #bsdcan #eurobsdcon #freebsd #openbsd #pf #packetfilter #networking #networktrickery […]

The Book of PF, 4th Edition: It’s Here, It’s Real © 2026 Peter N. M. Hansteen

The Book of PF, 4th Edition: It's Here, It's Real medium.com/@peter.hanst... #bookofpf #openbsd #freebsd #pf #packetfilter #networking #firewall #networktrickery @nostarchpress.bsky.social

Original post on mastodon.social

Yes, You Too Can Be An Evil Network Overlord - On The Cheap With OpenBSD, pflow And nfsen nxdomain.no/~peter/yes_you_too_can_b...

A story about network metadata and #openbsd, originally from 2014, good for reprising. See The Book of PF for more #nfsen #netflow […]

Original post on mastodon.social

The fresh 4th edition of The Book of PF in physical form has reached Europe (Ireland), www.linkedin.com/posts/tomsmythconnect_th... - so my stack of author copies are hopefully on the way too.

The book home page is at […]

Valuable News – 2026/02/09 The Valuable News weekly series is dedicated to provide summary about news, articles and other interesting stuff mostly but not always related to the UNIX/BSD/Linux systems. Whenever I stumble upon…

The latest Valuable News by @vermaden.bsky.social vermaden.wordpress.com/2026/02/09/v... notes that The Book of PF, 4th edition nostarch.com/book-of-pf-4... has been released #bookofpf #openbsd #freebsd #networking #pf @nostarchpress.bsky.social

Valuable News – 2026/02/09 The Valuable News weekly series is dedicated to provide summary about news, articles and other interesting stuff mostly but not always related to the UNIX/BSD/Linux systems. Whenever I stumble upon something worth mentioning on the Internet I just put it here. Today the amount information that we get using various information streams is at massive […]

The latest Valuable News by @vermaden vermaden.wordpress.com/2026/02/09/valuable-news... notes that The Book of PF, 4th edition https://nostarch.com/book-of-pf-4th-edition has been released #bookofpf #openbsd #freebsd #networking #pf @nostarch

Original post on mastodon.social

Upcoming "Network Management with the OpenBSD Packet Filter Toolset" tutorials (covering #freebsd and #openbsd):

2026-03-19 AsiaBSDCob https://www.asiabsdcon.org
2026-06-18 BSDCan https://www.bsdcan.org

See nxdomain.no/~peter/pf_tutorial_upcom... ( […]

girl studies the ancient tome of PF

acquired - tome of pf

(this is not sponsored content, I just like the book)

thank you @pitrh

https://nostarch.com/book-of-pf-4th-edition

#unix_surrealism #comic #technomage #openbsd #pf #bookofpf

The Book of PF, 4th Edition Build a more secure network with PF.

I suppose I forgot to tell you that if you order The Book of PF, 4th ed nostarch.com/book-of-pf-4... now, you'll get the *final version* ebook (print soon) #bookofpf #openbsd #freebsd #networking #firewalls #pf #networktrickery #freesoftware #libresoftware @nostarch
Also nxdomain.no/~peter/yes_t...

Original post on mastodon.social

Oh, I suppose I have been slacking and not telling you that if you order The Book of PF, 4th ed https://nostarch.com/book-of-pf-4th-edition now, you will get the *final version* ebook (print is still in progress) #bookofpf #openbsd #freebsd #networking #firewalls #pf #networktrickery […]

The recording from NYC*BUG Saturday January 10th, 2026 session "The Book of PF 4th ed + EU CRA: It's time to Engineer up" is now available:
Youtube: youtu.be/HOCsvcCm1Ec
Peertube: toobnix.org/w/bQPtKXKqJM...
#bookofpf #OpenBSD #freebsd #packetfilter #CRA #SBOMS #dependency #supplychain #security

Why 451 is Good for You - Greylisting Perspectives From the Early Noughties

Why 451 is Good for You - Greylisting Perspectives From the Early Noughties nxdomain.no/~peter/why_4... (tracked bsdly.blogspot.com/2025/12/why-...) @nostarch #greytrapping #greylisting #smtp #email #spam #antispam #bookofpf

Why 451 is Good for You - Greylisting Perspectives From the Early Noughties © 2025 Peter N. M. Hansteen _A software vendor was using SMTP spamware to send license keys customers had paid thousands for. A measured rant was in order, and turned out to be quite enlightening._ While looking thrugh directories of old material, I stumbled upon what was most likely the main part of a complaint sent to a software vendor for failing to deliver a license key file the company I worked for then had paid some thousands of dollars for. The file as I found it was dated August 2010, but was likely a preserved copy of a draft that was written some time before the first edition of _The Book of PF_ (now in its _fourth edition_) was published, in response to the non-delivery incident. A quick investigation had me conclude from my `spamd` logs that their side did not play well with _greylisting_. * * * **Note:** This piece is also available _without_ trackers but _classic_ formatting only here. * * * I have revisited the _handling sites that do not play well with greylisting_ theme a number of times, such as the 2018 piece _Goodness, Enumerated by Robots. Or, Handling Those Who Do Not Play Well With Greylisting_ (also _here_). But I found these early notes interesting enough that I include them here, with only minor redactions to protect the (relatively) innocent: ` SWCrafters' reaction to finding out that their messages do not get through, essentially blaming "inaccurate spam filtering" was not unexpected, but I will take the opportunity to explain a few things about how Internet email works and how this makes their position at odds with reality. Even though Internet services are offered with no guarantees, usually described as 'best effort' services, a significant amount of effort has been put into making essential services such as SMTP email transmission fault tolerant, making the 'best effort' one with as close as does not matter to having a perfect record for delivering messages. The EXECUTIVE SUMMARY of this message is that the matter which trips up the delivery of SWCrafters' license-carrying emails is the fact that their email sending software's best effort at delivery falls significantly short of what current Internet standards require. The current standard for Internet email transmission is defined in RFC2821, which in section 4.5.4.1, "Sending Strategy", states > "In a typical system, the program that composes a message has some method for requesting immediate attention for a new piece of outgoing mail, while mail that cannot be transmitted immediately MUST be queued and periodically retried by the sender." and > "The sender MUST delay retrying a particular destination after one attempt has failed. In general, the retry interval SHOULD be at least 30 minutes; however, more sophisticated and variable strategies will be beneficial when the SMTP client can determine the reason for non-delivery." Contrast this with the application which sends the SWCrafters license information messages, which according to the data I have avaliable opens two SMTP sessions within a second of each other (the time resolution I have in my logs at the moment), apparently discarding the message without delivery afterwards. RFC2821 goes on to state that > "Retries continue until the message is transmitted or the sender gives up; the give-up time generally needs to be at least 4-5 days." After all, delivering email is a collaborative, best effort thing, and he RFC states clearly that if the site you are trying to send mail to reports it can't receive anything at the moment, it is your DUTY (a MUST requirement) to try again later, after an interval which is long enough that your unfortunate communication partner has had a chance to clear up whatever was the problem. A sending strategy which relies on every receiver to be receptive at all times, discarding undelivered messages after only one unsuccessful attempt, possibly makes sense if the data you are sending is unimportant or if your intended targets are unlikely read or even want to receive the messages you send. If on the other hand the data you are sending matter to either you or the intended recipient, it is in everybody's interest that you use the fault tolerance features which a compliant SMTP mail system offers. To put this in context, you need to remember that the SWCrafters license messages are the result of some SWCrafters customer ordering at least a thousand dollars' worth or software licenses, with no real upper limit on the dollar value of a single message. The system used to send these messages apparently does not understand SMTP status messages, discarding undelivered messages without a trace. Essentially, the system you are using treats the data your customers expect to receive in exchange for thousands of dollars paid as discardable. The "greylisting" technique which is in use at justgottahave.faith and other sites means that our systems expect any SMTP sender to understand SMTP status codes and to respect "451 temporary error please try again later" messages. The hows and whys are detailed at https://www.greylisting.org/, with a tutorial which contains a 'close enough' description of how it's done at datadok to be found at https://home.nuug.no/~peter/pf/, with the particulars starting at https://home.nuug.no/~peter/pf/en/spamd.html. We do content filtering as well, but this particular application never managed to get its data sent far enough to encounter content filtering until its IP address got whitelisted (listed as 'known good', or if you will, not having to conform to normal criteria). Greylisting works extremely well, and since it is both standards compliant (essentially insisting on compliance) and simple to implement you should expect it to be deployed at the next site you are trying to send email to. ` If I remember correctly, the other side found a way to send the missing license codes with something that _did_ handle SMTP status codes correctly a short time after the mail that included some version of these notes was sent. I had originally intended to make the URLs in the text here clickable, but changed my mind when I discovered that the current operators of `greylisting.org` have decided that a _large language model_ (the current iteration of what passes for _artificial intelligence_ needed to be included in the processing. That will perhaps serve as a sign that the world does move on, if not necessarily in useful directions at all times. If you want to explore the ins and outs of greylisting and the related phenomenon _greytrapping_ , my recent piece _Eighteen Years of Greytrapping - Is the Weirdness Finally Paying Off?_ (also _here_) is a way to start. For the greylisting part, the notes above capture the main points. * * * _Why 451 is Good for You - Greylisting Perspectives From the Early Noughties_ is © 2025 Peter N. M. Hansteen (published 2025-12-28) * * * You might also be interested in reading selected pieces via _That Grumpy BSD Guy: A Short Reading List_ (also _here_). Separately, pre-orders of _The Book of PF, 4th edition_ are now open. For a little background, see the blog post _Yes, The Book of PF, 4th Edition Is Coming Soon_ (also _here_). The latest information I have is that physical copies should be ready to ship by the end of January 2026. * * *

Why 451 is Good for You - Greylisting Perspectives From the Early Noughties https://nxdomain.no/~peter/why_451_is_good.html (tracked bsdly.blogspot.com/2025/12/why-451-is-good-... @nostarch #greytrapping #greylisting #smtp #email #spam #antispam #bookofpf

Valuable News – 2025/12/08 The Valuable News weekly series is dedicated to provide summary about news, articles and other interesting stuff mostly but not always related to the UNIX/BSD/Linux systems. Whenever I stumble upon…

The latest Valuable News by @vermaden vermaden.wordpress.com/2025/12/08/v... notes that The Book of PF, 4th edition is coming soon (also nxdomain.no/~peter/yes_t..., bsdly.blogspot.com/2025/07/yes-...) @nostarch #freebsd #openbsd #pf #packetfilter #bookofpf #4thedition

Yes, The Book of PF, 4th Edition Is Coming Soon

Long rumored and eagerly anticipated by some, the fourth edition of The Book of PF is now available for preorder

More: nxdomain.no/~peter/yes_t... (bsdly.blogspot.com/2025/07/yes-...), nostarch.com/book-of-pf-4... @nostarch #openbsd #freebsd #pf #networking #bookofpf #freesoftware #firewalls

And I should add -

* we are making final tweaks to labs and slides still
* we will be covering #FreeBSD 14 as well as #OpenBSD, with labs supporting both.

Original post on mastodon.social

My upcoming book, The Book of PF 4th edition, is part of B&N’s pre-order sale Sept 3–5! Use code PREORDER25 for 25% off (35% for Premium members).

www.barnesandnoble.com/w/the-book-of-pf-4th-edi...

#bookofpf #bnpreorder #openbsd #freebsd […]

The Book of PF, 4th Edition: A No-Nonsense Guide to the OpenBSD Firewall|Paperback The Book of PF, 3rd Edition is the essential guide to building a secure network with PF, the OpenBSD packet filtering tool.The OpenBSD packet filter, PF, is central to the OpenBSD and FreeBSD network ...

My upcoming book, The Book of PF 4th edition, is part of B&N’s pre-order sale Sept 3–5! Use code PREORDER25 for 25% off (35% for Premium members).

www.barnesandnoble.com/w/the-book-o...

#bookofpf #bnpreorder #openbsd #freebsd #pf #packetfilter #networking #security #nostarch #barnesandnoble

Yes, The Book of PF, 4th Edition Is Coming Soon

"Yes, The Book of PF, 4th Edition Is Coming Soon" nxdomain.no/~peter/yes_t... (also bsdly.blogspot.com/2025/07/yes-...), title still true, actual publication date TBD, #bookofpf #pf #packetfilter #openbsd #freebsd #networking #security #trickery #hacking

Original post on mastodon.social

"Yes, The Book of PF, 4th Edition Is Coming Soon" nxdomain.no/~peter/yes_the_book_of_p... (also bsdly.blogspot.com/2025/07/yes-book-of-pf-4... title still true, actual publication date TBD, #bookofpf #pf #packetfilter #openbsd #freebsd […]

Original post on mastodon.social

The latest BSD Weekly https://bsdweekly.com/issues/245 features "Eighteen Years of Greytrapping ..." (nxdomain.no/~peter/eighteen_years_of... and bsdly.blogspot.com/2025/08/eighteen-years-o... - a warmup to #bookofpf 4th ed […]

Yes, The Book of PF, 4th Edition Is Coming Soon

Yes, The Book of PF, 4th Edition Is Coming Soon nxdomain.no/~peter/yes_t... (also tracked bsdly.blogspot.com/2025/07/yes-...) #openbsd #freebsd #bookofpf #pf #packetfilter #book #networking #security #freesoftware #libresoftware #shamelessplug

Original post on mastodon.social

Yes, The Book of PF, 4th Edition Is Coming Soon nxdomain.no/~peter/yes_the_book_of_p... (also tracked bsdly.blogspot.com/2025/07/yes-book-of-pf-4... #openbsd #freebsd #bookofpf #pf #packetfilter #book #networking #security #freesoftware […]

The Book of PF, 4th Edition Build a more secure network with PF.

We are still working on The Book of PF 4th ed.
Preorder: nostarch.com/book-of-pf-4..., read about the work nxdomain.no/~peter/yes_t... (also tracked at bsdly.blogspot.com/2025/07/yes-...) #bookofpf #newedition #freebsdd #openbsd #pf #packetfilter #networking #security #freesoftware #libresoftware

Original post on mastodon.social

We are still working on The Book of PF, 4th ed.

Preorders are open at https://nostarch.com/book-of-pf-4th-edition read about the work at nxdomain.no/~peter/yes_the_book_of_p... (also tracked at […]

Yes, The Book of PF, 4th Edition Is Coming Soon © 2025 Peter N. M. Hansteen Long rumored and eagerly anticipated by some, the fourth edition of The Book of PF is now available for p...

oh, my "Yes, The Book of PF, 4th Edition Is Coming Soon" bsdly.blogspot.com/2025/07/yes-... is on hackernews: news.ycombinator.com/item?id=4465... #bookofpf #pf #packetfilter #openbsd #freebsd #networking (non-tracked: nxdomain.no/~peter/yes_t...)

Original post on mastodon.social

oh, my "Yes, The Book of PF, 4th Edition Is Coming Soon" bsdly.blogspot.com/2025/07/yes-book-of-pf-4... is on hackernews: https://news.ycombinator.com/item?id=44657803 #bookofpf #pf #packetfilter #openbsd #freebsd #networking (non-tracked […]