Debian #751288: Avahi-daemon is noisy

[lathiat]

Package: avahi-daemon
Version: 0.6.31-4

Avahi-daemon fills my logs with

Jun 11 07:38:57 lanthane avahi-daemon[2502]: Invalid response packet from host 172.23.36.97.
Jun 11 07:39:56 lanthane avahi-daemon[2502]: Invalid response packet from host 172.23.43.78.
Jun 11 07:39:56 lanthane avahi-daemon[2502]: Invalid response packet from host 172.23.36.97.

This will become a big problem as apparently Windows 10 causes this.

See also https://bugs.launchpad.net/ubuntu/+source/avahi/+bug/1342400
which references a patch that would help (haven't tested it myself yet,
may do today).

Maybe this bug needs to be merged with #639163
(which is already merged with #688061, although IMHO that's a different
problem).

Paul

[jmaggard10]

The patch in that bug deals with OSX mDNS response packets that include Additional RRs, but do not include Answer RRs.

Windows 10 does something different. It sends responses to all mDNS queries, whether or not it has any records for those requests. That is, it responds with a mDNS packet containing 0 Answer RRs and 0 Additional RRs. This appears to me to be in violation of RFC 6762 (Multicast DNS) Section 6, which states "A Multicast DNS responder MUST only respond when it has a positive, non-null response to send, or it authoritatively knows that a particular record does not exist." I don't know how to file a bug with Microsoft, but IMHO this should probably be addressed on their side.

[jmaggard10]

Maybe something like this makes sense?

diff --git a/avahi-core/server.c b/avahi-core/server.c
index e87f035..18b1c84 100644
--- a/avahi-core/server.c
+++ b/avahi-core/server.c
@@ -972,8 +972,14 @@ static void dispatch_packet(AvahiServer *s, AvahiDnsPacket *p, const AvahiAddres
             return;
         }

+        if (avahi_dns_packet_get_field(p, AVAHI_DNS_FIELD_ANCOUNT) == 0 &&
+            avahi_dns_packet_get_field(p, AVAHI_DNS_FIELD_ARCOUNT) == 0) {
+
+            avahi_log_debug("Received empty response packet from host %s.", avahi_address_snprint(t, sizeof(t), src_address));
+            return;
+        }
+
         if (avahi_dns_packet_get_field(p, AVAHI_DNS_FIELD_QDCOUNT) != 0 ||
-            avahi_dns_packet_get_field(p, AVAHI_DNS_FIELD_ANCOUNT) == 0 ||
             avahi_dns_packet_get_field(p, AVAHI_DNS_FIELD_NSCOUNT) != 0) {

             avahi_log_warn("Invalid response packet from host %s.", avahi_address_snprint(t, sizeof(t), src_address));

[jgkamat]

Is this eventually going to be fixed? This has become a huge problem on the network I am on...

[StuntsPT]

I second that.
My logs are getting hammered with 20+ of these lines per second...

[da2x]

Steps to reproduce in Windows 10:

1. Open Settings app: Devices: Printers and scanners
2. Click Add printers and scanners

Trivia: mDNS is used by printer network stack, and the API is also exposed to WinJS apps (JavaScript based “modern” apps) only. Also available on Windows 10 Mobile.

[bcomnes]

Yay! Thanks for solving this long running issue! Any ideas when it will make it into a release?

[da2x]

@bcomnes check the project website at http://avahi.org/

[da2x]

The bug have also been fixed in the latest Windows Insider build. No idea when this stuff will roll out to regular Windows 10 users.

Update: Fix should have been deployed to all users on Windows Update now.

[bcomnes]

As I still have windows 7-8 systems on the networks I'm still happy to see this fixed :). Journalctl will be a lot less noisy