rDNS might not work on latest macos

[richstokes]

sudo bandwhich                                                            
Password:
Error: Could not initialize the DNS resolver. Are you offline?

bandwhich                                                                         
Error:

 lo0: No such file or directory (os error 2)
 en5: No such file or directory (os error 2)
 en0: No such file or directory (os error 2)
 awdl0: No such file or directory (os error 2)
 llw0: No such file or directory (os error 2)
 utun0: No such file or directory (os error 2)
 utun1: No such file or directory (os error 2)
 utun2: No such file or directory (os error 2)
 utun3: No such file or directory (os error 2)

uname -a                                                                                    
Darwin RMBP.local 19.4.0 Darwin Kernel Version 19.4.0: Wed Mar  4 22:28:40 PST 2020; root:xnu-6153.101.6~15/RELEASE_X86_64 x86_64

bandwhich -V                                                                     
bandwhich 0.13.0

Installed via homebrew

[imsnif]

Hey, thanks for reporting this. That's quite odd. Would you mind helping me out with a little bit of debugging to find the issue? (I don't have access to a mac)

If you run bandwhich with the -n flag like this sudo bandwhich -n does it work? Do you see traffic? (This turns off the reverse DNS resolution, which is what's failing here).

[richstokes]

That works!

[imsnif]

Hey @richstokes, so if you use the same terminal window from which you run bandwhich (when it doesn't work, without the -n flag) in order to do a ping github.com, does it work for you? This error essentially means that bandwhich failed to contact your DNS server, and I'm wondering why?

[richstokes]

Yep, DNS works fine for other apps;

sudo bandwhich                                      
Password:
Error: Could not initialize the DNS resolver. Are you offline?

nslookup google.com                                       
Server:		9.9.9.9
Address:	9.9.9.9#53

Non-authoritative answer:
Name:	google.com
Address: 172.217.0.46

[imsnif]

Hum... just for debugging, would you be willing to try setting your dns server to 1.1.1.1 and seeing if it works out (with both bandwhich and nslookup)?

[richstokes]

Sure. Switched DNS to 1.1.1.1, cleared cache, retried, same error.

[imsnif]

Thanks! I'd like to give you a debug branch that'll give us a more verbose error in this case with a quick hack. Would you be comfortable running such a branch from this repo? I can provide some instructions if you're unfamiliar with rust.

[richstokes]

Can do when I have a few moments spare - not used Rust so would need info on how to compile/run

[DianaNites]

Same error here on Arch Linux, Could not initialize the DNS resolver, using systemd-resolved and googles DNS, 8.8.8.8, the -n flag works tho.

[Ma27]

@richstokes @DianaNites any chance you're running systemd-networkd at v246? It seems as the resolv-conf doesn't support the trust-ad option in /etc/resolv.conf at version 0.6.2 (which is the one we're using here).

The problem gets fixed on master (https://github.com/tailhook/resolv-conf/commit/83c0f25ebcb0615550488692c5213ca1ae4acd8f), so it should be possible to fix this issue by updating the resolv-conf crate to this revision.

I stumbled upon this issue after my latest OS update (which included systemd-246) which uses options trust-ad in their /etc/resolv.conf-stub for resolvectl. See https://github.com/systemd/systemd/commit/a742f9828ea73d9c2c9bafe701c10fe60f058012.

@imsnif I only confirmed that resolv-conf master fixes the issue. I'll try to fix the dependency for bandwhich and open a PR then :)

[imsnif]

Thanks very much for finding this @Ma27, and for the quick fix. My apologies for not finding the time for debugging this myself.

[Ma27]

Hmm I'm actually realizing now that the reporter has the issue on macos, so I don't if they have the same issue. However my patch fixes the issue for me.

[imsnif]

At the very least we'll get clearer errors after your patch on this.

[black-puppydog]

FWIW I was seeing this on an ubuntu install (rolling rhino, thieir kinda rolling release) and installing from git with the patch for resolv.conf actually did fix it for me

[DianaNites]

@Ma27 I'm on Arch Linux, which indeed uses systemd-networkd 246.

The latest bandwhich version, 0.19.0, does not fix it for me, though the error is now more detailed.

Error: Could not initialize the DNS resolver. Are you offline?

Reason: ResolveError { inner: Custom { kind: Other, error: "Error parsing resolv.conf: InvalidOption(17)" }

io error }

/etc/resolv.conf looks like this

nameserver 127.0.0.53
options edns0 trust-ad

[imsnif]

Hey @DianaNites (and others experiencing this issue),

I added a feature that would allow users to explicitly specify a dns server to use for the rDNS lookups as a workaround. Something like bandwhich --dns-server 1.1.1.1

I'm going to release a new version with it in the next few days (I'm waiting on another fix I'd like to see in that version too). Thanks for your patience. :)

[imsnif]

New version released. Starting from version 0.20.0, you can now use the --dns-server flag eg. bandwhich -d 1.1.1.1 to manually specify a DNS server as a workaround for this issue.

[cyqsimon]

Closing this issue as completed. If you disagree please comment/reopen.