Package: avahi-daemon Version: 0.6.31-2ubuntu4.1 Severity: wishlist Dear Maintainer,
There are many reports of avahi failing with the symptom that advertised services "disappear" after a short time. A typical example is bug #657553. There is a simple reason for why this happens on many home networks. This wishlist bug is a suggestion for how to fix it. Here is the reason for the failure. The mDNS service uses multicast UDP packets. The multicast protocol requires that one of the routers on a network be elected as an IGMP querier. It should broadcast IGMP query packets at regular intervals. The hosts which want to belong the mDNS multicast group (namely any computer running avahi-daemon) would then respond with its address. However, most home routers do not provide a multicast querier. On the other hand, most home switches and wireless access points do support IGMP snooping. The consequence of this is that the switch or WAP will unsubscribe hosts from the mDNS multicast group if the switch does not hear any IGMP responses from the host during that time. This causes the host to "disappear" as reported in bug #657553. Here is the simple fix. The avahi daemon should always start up as an IGMP querier, sending IGMP query packets at a configurable regular interval. The avahi daemon should also participate in the querier election process. That is, if it hears a query packet from another device with a lower IP address, then it should stop sending query packets. This way, if there is a true multicast router on the network the avahi-daemon will behave as it now does. But if, as is typical in home networks, there is no IGMP querier on the network then one of the avahi-daemons will step in. I have tested this on my home network by running a daemon on one of my linux systems which sends and IGMP query packet every 60 seconds. If that daemon is not running I see the same "disappearing addresses" as are reported in bug #657553. However, with the daemon running I am able to use .local addresses for all of my devices that support mDNS and service discovery for printers etc. works reliably. -- System Information: Debian Release: wheezy/sid APT prefers saucy-updates APT policy: (500, 'saucy-updates'), (500, 'saucy-security'), (500, 'saucy'), (100, 'saucy-backports') Architecture: amd64 (x86_64) Foreign Architectures: i386 Kernel: Linux 3.11.0-14-generic (SMP w/4 CPU cores) Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8) Shell: /bin/sh linked to /bin/dash Versions of packages avahi-daemon depends on: ii adduser 3.113+nmu3ubuntu2 ii bind9-host [host] 1:9.9.3.dfsg.P2-4ubuntu1.1 ii dbus 1.6.12-0ubuntu10 ii libavahi-common3 0.6.31-2ubuntu4.1 ii libavahi-core7 0.6.31-2ubuntu4.1 ii libc6 2.17-93ubuntu4 ii libcap2 1:2.22-1.2ubuntu2 ii libdaemon0 0.14-2build1 ii libdbus-1-3 1.6.12-0ubuntu10 ii libexpat1 2.1.0-4 ii lsb-base 4.1+Debian11ubuntu4 ii sysv-rc 2.88dsf-41ubuntu3 ii upstart 1.10-0ubuntu7 Versions of packages avahi-daemon recommends: ii libnss-mdns 0.10-3.2ubuntu1 Versions of packages avahi-daemon suggests: ii avahi-autoipd 0.6.31-2ubuntu4.1 -- Configuration Files: /etc/avahi/avahi-daemon.conf changed [not included] -- no debconf information -- To UNSUBSCRIBE, email to debian-bugs-dist-requ...@lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org
