OPNsense Forum

English Forums => 19.1 Legacy Series => Topic started by: Stilez on February 10, 2019, 05:20:45 pm

Title: I thought I understood mDNS/Airplay, but now having HP dns_sd - how to handle?
Post by: Stilez on February 10, 2019, 05:20:45 pm
I thought that I understood the way that Apple services, HP printers with Airplay implemented, and other such services worked on a segmented LAN.  The LAN here has a transparent WIFI AP that bridges wireless devices to OPT3, and filter rules on OPT3 allow access to the local resolver (Unbound: it's a small LAN with maybe <12 devices needing a static IP) and the LAN itself.

As I've understood it, devices broadcast requests/discovery announcements to their segment (bridged if needed by mdnsrepeater/avahi), and discover other devices on the LAN that way.  Irritating to have to bridge, but okay, doable.

Just now I hit a completely new thing in the zero-config realm, and I'm trying to understand how to integrate that into my LAN. I tried to use my printer from my mobile phone. The HP print service couldn't find the printer, but I could easily reach its built-in web UI from my phone, so TCP/UDP all work fine between the phone and printer. Intrigued, I ran tcpdump and found the HP Android print server plugin was sending odd DNS requests, which I now know are dns-sd packets, to the local LAN resolver, to try and find presumably statically coded or dynamic discovery records of local services.

The domain's it's looking for(initially at least) are: lb._dns-sd._udp.MY.DOMAIN and b._dns-sd._udp.MY.DOMAIN

This has thrown me on many levels. Please help me work out what to do!

I take a guess that it's piggybacking on (or similar to) Apple Airplay, and HP uses this as a kind of subnet-aware zeroconf autodiscovery, where device details are dumped into DNS TXT strings by local dns-sd aware devices, and DNS can be interrogated for them by service users. That leaves me 3 questions:

Title: Re: I thought I understood mDNS/Airplay, but now having HP dns_sd - how to handle?
Post by: newsense on February 10, 2019, 08:32:32 pm
Do you have DHCP Static Mapping and TXT Comment Support checked in Unbound - General ?