Please refer https://bugs.freedesktop.org/show_bug.cgi?id=51501 History :: =========== As pointed out by Simon McVittie in https://bugs.freedesktop.org/show_bug.cgi?id=51501#c4, https://tools.ietf.org/html/draft-cheshire-dnsext-multicastdns-15#section-10 suggests that the Time-To-Live (TT) of the mDNS record is likely to be 120 seconds. However, for all purposes, in whatever testing I came across Avahi, the TTL in effect was 75 minutes , which seemed a bit too late a notification of buddy-going-disconnected. Fix :: ====== Decrease the Time-To-Live (TTL). Solution :: =========== Obviously, the easiest solution is to set the appropriate values in #define AVAHI_DEFAULT_TTL_HOST_NAME #define AVAHI_DEFAULT_TTL However, this has the following caveats :: (i) It needs a re-compilation/re-packaging of avahi rpms, for every change in the values. This is a major deployment headache. (ii) Also, there is no ideal "TTL" values. The lesses the TTL values, more frequent multicast DNS packets will be exchanged between a pair of peers, thus leading to more traffic. However, too large a TTL value, would mean that the peer gets too late a notification of the buddy going disconnected. Thus, ideal values can only be found out by testing in real-field. This requires easy configuration of the TTL values, without needing to re-compile the rpms. Solution-Implementation :: ========================== The cutomized TTL values will be read during "avahi-daemon" startup. 1. AVAHI_DEFAULT_TTL_HOST_NAME will be set to the value, contained in the file "/etc/avahi/avahi-default-ttl-host-name.conf". Default value is the same as before, i.e. 120 (seconds). 2. AVAHI_DEFAULT_TTL will be set to the value, contained in the file "/etc/avahi/avahi-default-ttl.conf". Default value is the same as before, i.e. 4500 (seconds), which is equal to 75 minutes. How to customize :: =================== a) "sudo service avahi-daemon stop" b) Change the values in the corresponding conf files. c) "sudo service avahi-daemon start" AUTHOR: Ajay Garg Thanks to :: Will Thompson Simon McVittie Xavier Claessens diff -uNr avahi-0.6.27/avahi-common/defs.h copy-avahi-0.6.27/avahi-common/defs.h --- avahi-0.6.27/avahi-common/defs.h 2010-06-26 05:44:35.496078496 +0530 +++ copy-avahi-0.6.27/avahi-common/defs.h 2012-07-06 13:49:53.079315001 +0530 @@ -345,11 +345,14 @@ /** @} */ +int get_avahi_default_ttl_host_name(); +int get_avahi_default_ttl(); + /** The default TTL for RRs which contain a host name of some kind. */ -#define AVAHI_DEFAULT_TTL_HOST_NAME (120) +#define AVAHI_DEFAULT_TTL_HOST_NAME get_avahi_default_ttl_host_name() /** The default TTL for all other records. */ -#define AVAHI_DEFAULT_TTL (75*60) +#define AVAHI_DEFAULT_TTL get_avahi_default_ttl() AVAHI_C_DECL_END diff -uNr avahi-0.6.27/avahi-common/load_ttl_config.c copy-avahi-0.6.27/avahi-common/load_ttl_config.c --- avahi-0.6.27/avahi-common/load_ttl_config.c 1970-01-01 05:30:00.000000000 +0530 +++ copy-avahi-0.6.27/avahi-common/load_ttl_config.c 2012-07-06 13:55:11.348315001 +0530 @@ -0,0 +1,32 @@ +#include + +int avahi_default_ttl_host_name; +int avahi_default_ttl; + + +int read_int_from_file(const char *filename) { + FILE *fp = NULL; + char line[128]; + + fp = fopen(filename, "r"); + fgets(line, 128, fp); + fclose(fp); + + return atoi(line); +} + + +int load_default_ttl_values() { + avahi_default_ttl_host_name = read_int_from_file(AVAHI_DEFAULT_TTL_HOST_NAME_CONFIG_FILE); + avahi_default_ttl = read_int_from_file(AVAHI_DEFAULT_TTL_CONFIG_FILE); +} + + +int get_avahi_default_ttl_host_name() { + return avahi_default_ttl_host_name; +} + + +int get_avahi_default_ttl() { + return avahi_default_ttl; +} diff -uNr avahi-0.6.27/avahi-common/Makefile.am copy-avahi-0.6.27/avahi-common/Makefile.am --- avahi-0.6.27/avahi-common/Makefile.am 2010-06-26 05:44:35.494078632 +0530 +++ copy-avahi-0.6.27/avahi-common/Makefile.am 2012-07-06 13:54:34.789315001 +0530 @@ -17,6 +17,12 @@ AM_CFLAGS=-I$(top_srcdir) +pkgsysconfdir=$(sysconfdir)/avahi + +AM_CFLAGS+= \ + -DAVAHI_DEFAULT_TTL_HOST_NAME_CONFIG_FILE=\"$(pkgsysconfdir)/avahi-default-ttl-host-name.conf\" \ + -DAVAHI_DEFAULT_TTL_CONFIG_FILE=\"$(pkgsysconfdir)/avahi-default-ttl.conf\" + # This cool debug trap works on i386/gcc only AM_CFLAGS+='-DDEBUG_TRAP=__asm__("int $$3")' @@ -66,7 +72,8 @@ watch.h gccmacro.h \ rlist.h rlist.c \ utf8.c utf8.h \ - i18n.c i18n.h + i18n.c i18n.h \ + load_ttl_config.c libavahi_common_la_CFLAGS = $(AM_CFLAGS) $(PTHREAD_CFLAGS) -DAVAHI_LOCALEDIR=\"$(avahilocaledir)\" libavahi_common_la_LIBADD = $(AM_LDADD) $(PTHREAD_CFLAGS) $(PTHREAD_LIBS) $(INTLLIBS) diff -uNr avahi-0.6.27/avahi-daemon/avahi-default-ttl.conf copy-avahi-0.6.27/avahi-daemon/avahi-default-ttl.conf --- avahi-0.6.27/avahi-daemon/avahi-default-ttl.conf 1970-01-01 05:30:00.000000000 +0530 +++ copy-avahi-0.6.27/avahi-daemon/avahi-default-ttl.conf 2012-07-06 13:49:53.059315001 +0530 @@ -0,0 +1 @@ +4500 diff -uNr avahi-0.6.27/avahi-daemon/avahi-default-ttl-host-name.conf copy-avahi-0.6.27/avahi-daemon/avahi-default-ttl-host-name.conf --- avahi-0.6.27/avahi-daemon/avahi-default-ttl-host-name.conf 1970-01-01 05:30:00.000000000 +0530 +++ copy-avahi-0.6.27/avahi-daemon/avahi-default-ttl-host-name.conf 2012-07-06 13:49:53.060315001 +0530 @@ -0,0 +1 @@ +120 diff -uNr avahi-0.6.27/avahi-daemon/main.c copy-avahi-0.6.27/avahi-daemon/main.c --- avahi-0.6.27/avahi-daemon/main.c 2010-07-13 06:27:19.331756055 +0530 +++ copy-avahi-0.6.27/avahi-daemon/main.c 2012-07-06 13:49:53.058315001 +0530 @@ -581,6 +581,8 @@ AvahiIniFile *f; AvahiIniFileGroup *g; + load_default_ttl_values(); + assert(c); if (!(f = avahi_ini_file_load(c->config_file ? c->config_file : AVAHI_CONFIG_FILE))) diff -uNr avahi-0.6.27/avahi-daemon/Makefile.am copy-avahi-0.6.27/avahi-daemon/Makefile.am --- avahi-0.6.27/avahi-daemon/Makefile.am 2010-06-27 04:21:50.566291478 +0530 +++ copy-avahi-0.6.27/avahi-daemon/Makefile.am 2012-07-06 13:49:53.056315001 +0530 @@ -67,6 +67,8 @@ pkgsysconf_DATA = \ avahi-daemon.conf \ + avahi-default-ttl-host-name.conf \ + avahi-default-ttl.conf \ hosts dist_service_DATA = \ @@ -154,6 +156,8 @@ EXTRA_DIST = \ avahi-daemon.conf \ + avahi-default-ttl-host-name.conf \ + avahi-default-ttl.conf \ example.service \ hosts \ example.service \