[avahi] localhost service discovery in offline mode

Remi Emonet remi-14-ecf2 at heeere.com
Sat Oct 9 13:48:59 PDT 2010

Dear avahi developers,

I would really like to have some feedback on my previous mail.
We are using avahi in the http://omiscid.gforge.inria.fr/ project. We 
want to push the project forward and want to know if we can count on 
avahi for localhost-only (offline) discovery or if we will have to 
duplicate the service discovery (e.g. using dbus) or find an alternative.

I found that my question is to some extent related to 
http://avahi.org/ticket/92 . I could also see some possible elements of 
"solution" in the patches from http://avahi.org/ticket/198 .

Also, now I can better reformulate my request for enhancement:
     When using for AvahiIfIndex: AVAHI_IF_UNSPEC = -1       /**< 
Unspecified/all interface(s) */,
     discovery through the local "lo" network interface should be enabled.

Thanks in advance for any feedback (even negative).

Le 30/09/2010 21:34, Remi Emonet a écrit :
> Hi all,
> I started using avahi more that 2 or 3 years back, mainly exploiting 
> the dns-sd aspect (service discovery). Avahi is working pretty well 
> but I have one case where it has a behavior that I do not expect. I 
> hope this mailing list is the right place for this (or should I rather 
> use the bug tracker even for non-bugs?).
> Here is the "problem": the computer is connected to a local network, 
> it publishes some services and is able to discover services on other 
> computers (no problem here), but, if I unplug the network cable (or 
> disable the local network connection) all services disappear, 
> including the ones declared on localhost. In our context, we would 
> have liked to keep the service discovery functionality even if the 
> host is totally isolated.
> Does anyone sees any way to tell avahi to continue working even if 
> only the loopback interface is "connected"?
> Don't hesitate to tell me if the objective or my problem is not clear.
> Here is a simple way to illustrate my point:
>  - have a network connection
>  - in terminal T1, start "avahi-browse    _lo._tcp"
>  - in terminal T2, start "avahi-publish-service   Heeere    
> _lo._tcp    8888"
> -> in T1 you get: "+ eth0 IPv4 Heeere  _lo._tcp  local"
>  - unplug the network cable (or disable the corresponding interface)
> -> in T1 you get: "- eth0 IPv4 Heeere  _lo._tcp  local"
> --> This means the services on localhost cannot discover each others 
> anymore.
> My current test configuration is an Ubuntu 10.04 LTS 64 bits, but I 
> have seen the same behavior with (all) other linux systems I've used 
> before.
> Thank you in advance for any help and comments you could provide.
> Best Regards,
> Rémi

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