On 11/04/2016 12:58 PM, Michael B Allen wrote: > On Fri, Nov 4, 2016 at 2:36 PM, Rick Stevens <ricks@xxxxxxxxxxxxxx> wrote: >> On 11/04/2016 11:09 AM, Tom Horsley wrote: >>> On Fri, 4 Nov 2016 13:03:41 -0400 >>> Michael B Allen wrote: >>> >>>> Is mDNS supposed to coexist with DNS? >>> >>> I have no idea what is "supposed" to work, but I know >>> I always have to get rid of the mdns [notfound=return] >>> crap that is in my /etc/nsswitch.conf file by default >>> in order to get "normal" dns lookups to work. >> >> Yeah, I've never figured out why they do that. The default action >> for notfound is "continue". Why they abort further lookups by using >> "return" is silly and (IMHO) broken. > > Ok, so this nails it. If I remove [notfound=return] then there is a 3 > second delay for mdns to return but it does fallback to DNS. I have to > completely remove mdns4_minimal [notfound=return] to just use DNS. > > Of course my local network is a .local domain so it seems at least in > my case mdns cannot really be used effectively. By removing [notfound=return], things are behaving as I'd expect. If you're not using Avahi (or Bonjours), there really isn't any valid reason to use mDNS. > I never understood these logical meta languages. Pam is another > example. It's basically just an obscure way of writing code so it's > not obvious to me why this isn't just scripted so that someone has the > option of making them work together (call both mDNS and DNS async and > then return first to respond). Historically, host resolution has never been a multithreaded process so it's never been done async (the API has no non-blocking versions of the function calls). Even without mDNS, the resolver library tries the first nameserver configured. If there's no answer to the query at all (e.g. server is down), it tries the second, then the third (if configured). The first answer received is used. If none of the servers respond at all or if all of the queries come back "not found", then the host isn't resolved. Note that you ARE talking over the Internet to get resolutions so you're stuck with the TCP/IP protocol timeouts along with the timeouts defined for the DNS service itself (60 seconds IIRC). You can shorten those (the original timeouts were chosen to handle slow links like dialup lines and such). Those are fairly rare now, but the timeouts remain. mDNS provides the Avahi protocol, which is the open source version of Apple's Bonjours, which, in turn, is Apple's attempt at something like Microslop's NetBIOS. The whole ".local" suffix is an attempt to wrap non-Internet related things into Internet-appearing parlance so the same libraries can be used. A good example of pushing a paradigm too far, if you ask me (which you aren't, but....) Where both mDNS and real DNS are active, if you parallelize the queries as you suggesting and get different answers, which answer gets credence? mDNS will almost always answer first since it's local to your machine so DNS would never be consulted and you'd just get "not found" out the wazoo. You could try setting publish-resolv-conf-dns-servers=yes in /etc/avahi/avahi-daemon.conf to have DNS results published and this may do what you want. We don't use mDNS here at the office, so my experience with it is limited and I haven't played with a lot of the various options. ---------------------------------------------------------------------- - Rick Stevens, Systems Engineer, AllDigital ricks@xxxxxxxxxxxxxx - - AIM/Skype: therps2 ICQ: 226437340 Yahoo: origrps2 - - - - To err is human. To forgive, a large sum of money is needed. - ---------------------------------------------------------------------- _______________________________________________ users mailing list -- users@xxxxxxxxxxxxxxxxxxxxxxx To unsubscribe send an email to users-leave@xxxxxxxxxxxxxxxxxxxxxxx
