www.doublefourteen.io/content/blog/bgpscanner-backwards-compat.md

title	mobile_menu_title	date	description	series	categories	tags	news_keywords
New bgpscanner backwards compatibility script released!	bgpscanner compatibility script is out!	2021-08-11	Meet the bgpscanner legacy wrapper - The Micro BGP Suite now provides mostly complete backwards compatibility with Isolario bgpscanner. You may use it to learn bgpgrep & peerindex or to run your legacy scripts easily.	ubgpsuite - The Micro BGP Suite	news development	ubgpsuite bgpscanner bgpgrep peerindex Networking BGP	ubgpsuite bgpscanner bgpgrep peerindex

New bgpscanner backwards compatibility script is now available.

Lately I had the pleasure to be in contact with many old time bgpscanner aficionados.

A question popped up frequently during our conversations.

• I used to do X with bgpscanner, can bgpgrep do the same, and how?

That's when the fact hit me, that bgpscanner probably had a larger userbase relying on it for day to day work than I originally anticipated. Unfortunately bgpgrep and peerindex are not exactly backwards compatible. While probably being very convenient to new users, it could throw off the experienced userbase that has been familiar with bgpscanner for years.

Even worse, it could make existing scripts instantly unusable.

This convinced me that providing a backwards compatibility feature might be a good idea to help users familiarize with the new tool while also providing a smoother transition curve.

Coming back to the recurring question, yes, bgpgrep, and peerindex, do anything bgpscanner can do.

To top it off, bgpgrep does what bgpscanner does not.

That was actually the most fundamental reason that encouraged me to break backwards compatibility. bgpgrep provides extreme flexibility in filtering specification, letting the user combine freely multiple conditions and chain them arbitrarily with AND, OR and NOT logic. Something bgpscanner could do only to a very limited extent. This while also being intuitive with its syntax.

But that doesn't eliminate the fact that bgpscanner was already pretty powerful by itself, and it did things in a different way. So what?

Enter the bgpscanner legacy wrapper script. The third tool in µbgpsuite arsenal (they grow so fast ♥).

A somewhat pragmatic, crude, grumpy -- yet fascinating in its own special way, POSIX shell wrapper script capable of converting (almost) any invocation of bgpscanner to an equivalent invocation of bgpgrep or peerindex. Making the bgpscanner legacy wrapper a drop-in replacement for the classic Isolario bgpscanner.

While this is satisfactory by itself, it didn't feel quite alright. In my book bgpscanner is still an obsolete tool (hence the "legacy" in "wrapper script"). Being able to actually learn how to do things with new tools would be much better than relying on the old ways.

This is when it hit me again, the wrapper script already does all the hard work to figure out how to make an equivalent call to µbgpsuite native tools. Why not just print the result, instead of executing it?

$ PRETEND=y bgpscanner -i 192.65.131.1 -p "137 2598$" -u 8.8.8.8/32 data/rib/bview.20181016.0800.gz
bgpgrep -- data/rib/bview.20181016.0800.gz -peer \( 192.65.131.1 \) -supernet \( 8.8.8.8/32 \) -aspath "137 2598$"

Isn't it awesome? With just a tiny PRETEND=y flag, we can now interactively learn how to convert an old invocation to the new format. True, it might not be the best, most expressive, most idiomatic way to write the query, but it is an excellent starting point.

You can install the bgpscanner legacy wrapper script along with other µbgpsuite tools by enabling the bgpscanner-legacy configuration option with meson, just run:

$ meson configure -Dbgpscanner-legacy=true

inside your µbgpsuite build directory and it will be installed along with the other tools upon ninja install.

Obviously, it wouldn't be a true announcement post, if I didn't also mention that the bgpscanner legacy wrapper script is documented in its own fantastic man page. And that you're just one command away from having a beautiful PDF with its contents:

$ sed s/@UTILITY@/bgpscanner/g tools/bgpscanner/bgpscanner.1.in | groffer

Hoping the bgpscanner legacy wrapper tool will be at least as useful to you as it was fun for me to write.

Happy hacking!

Lorenzo Cogotti

P.S. A gigantic and special thank you to Rich's sh (POSIX shell) tricks, for its enlightening list of shell recipes. In my opinion one of the most fundamental reads that anybody writing a shell script should go through.