Yes this is currently correct. Avahi needs a way to see a list of interfaces and IP addresses as well to monitor when they are added and removed. Currently the only interface for that on Linux is netlink.
If you want to go without it you’d have to write a replacement iface-*.c code to leverage whatever APIs are available. What’s your use case? Trent > > On 28 Feb 2022, at 1:47 am, Jonathan Bagg <jb...@lenbrook.com> wrote: > > Hello, > > I have built libavahi-core.a from source without netlink support on Linux > (x86 Debian 11). Why --> Google has disabled binding to a netlink socket in > api >= 30. Unfortunately my program is not able to publish or browse for > services without netlink enabled in avahi-core. Is this correct behaviour? > I noticed iface-none.c is built instead of iface-linux.c. > > Jon > >> On 2021-12-07 8:24 p.m., Trent Lloyd wrote: >> Hi Folkert, >> >>>> On 8 Dec 2021, at 4:56 am, folkert <folk...@vanheusden.com> wrote: >>> >>>> I made a program which sends an mDNS announcement every 121 seconds. >>>> The TTL is 120 seconds. >>>> >>>> Yet every time avahi (with --debug) complains about: >>>> >>>> dec 07 10:27:54 lappiemctopface avahi-daemon[937]: Received conflicting >>>> record [_apple-midi._udp.local IN PTR >>>> mymdnstest._apple-midi._udp.local ; ttl=120]. Resetting our record. >>>> >>>> I've uploaded a pcap: >>>> https://linkprotect.cudasvc.com/url?a=https%3a%2f%2fvps001.vanheusden.com%2f~folkert%2fmdns.pcap&c=E,1,qAnUYiH7cFCdxQbDZpGLALJ3CssMNFzEVwiE1YbVHM6xWACOIfv0bXq4NyQO47Se-scGGdgXM8Y-4LPX_zaw-lMTYcZTObE8F7JZtvBCze4WWoAqIg,,&typo=1 >>>> (text dump: >>>> https://linkprotect.cudasvc.com/url?a=https%3a%2f%2fvps001.vanheusden.com%2f~folkert%2fmdns.txt&c=E,1,j_MXzszdG-MCfApSpw2sf4M8LBrQJcvTlDZUHKUshzPaBaT2VINalQ-vLxTh1PcaTI7hzfBzJ8GIdmcqriVdhknuL4iP35MAIF2fNwH9jQZ_2tNyB-AAdodHqJs,&typo=1 >>>> ) >>>> >>>> Anyone an idea what is going wrong? >>> I just verified that I get this error already on the first packet. >>> >>> So I start avahi-daemon, let the other program send the mdns message >>> once and immediately avahi complains about a conflicting record. >> What is sending these other packets? I think there are two main problems. >> The first one leading to the immediate conflict is that mDNS records can be >> either “Unique” (owned by a single host) or “Shared” (a record publish by >> multiple hosts, or, a list of records published in aggregate by multiple >> hosts). >> >> If you refer to RFC6762 Section 10.2 >> (https://linkprotect.cudasvc.com/url?a=https%3a%2f%2fdatatracker.ietf.org%2fdoc%2fhtml%2frfc6762%23section-10.2&c=E,1,hRneuq7gmccKO3LOVORaP2tWQygWE5bJiKLRQha1JzYmzqty-tJg-1qQYtkUu_e_UjO2kU6ACgPcwFQz4fxni2UFlKtmaHdTPZhuKufxrZxAWjuemctkl_UUwB8,&typo=1) >> >> The semantics of the cache-flush bit are as follows: normally when a >> resource record appears in a Resource Record Section of the DNS >> response it means, "This is an assertion that this information is >> true". When a resource record appears in a Resource Record Section >> of the DNS response with the cache-flush bit set, it means, "This is >> an assertion that this information is the truth and the whole truth, >> and anything you may have heard more than a second ago regarding >> records of this name/rrtype/rrclass is no longer true”. >> >> >> Unique records such as your hostname ‘mydnstest.local’ are expected to have >> the cache-flush bit to be set. But for shared resources such as the list of >> services (_apple-midi._udp.local PTR) we expect a “Shared” record so the >> cache-flush bit is false. This is because the “_apple-midi._udp.local” >> record is a shared list of services where multiple services all contribute >> to the list. >> >> Additionally the SRV record looks wrong.. from your text output it says: >> _apple-midi._udp.local: type SRV, class IN, cache flush, priority 0, >> weight 0, port 5004, target mymdnstest.local >> >> The name of this record should be ‘mydnstest._apple-midi._udp.local’ >> instead, the same name as the target for the PTR record. >> >> >> The hierarchy of announcements is: >> (1) PTR from the shared service name (_http._tcp) with a target of your >> unique service instance (test._http._tcp.local) >> >> _http._tcp.local PTR test._http._tcp.local (Shared record, cache-flush=false) >> >> (2) SRV record from your unique service name with the port number and target >> hostname >> test._http._tcp.local SRV port 80 target primary.local (Non-shared record, >> cache-flush=true) >> >> There may also be a TXT record of the same name with any properties >> >> (3) A/AAAA record for the IP address of the target hostname referenced in >> the SRV (the hostname is usually shared by all services from the same host) >> primary.local A 192.168.1.1 (Typically non-shared with cache-flush=true) >> >> Here is an example Wireshark capture I took just now of publishing a service >> using avahi (avahi-publish-service test _http._tcp 80). I’d suggest >> reviewing and comparing your announcement to that: >> >> test._http._tcp.local: type TXT, class IN, cache flush >> Name: test._http._tcp.local >> Type: TXT (Text strings) (16) >> .000 0000 0000 0001 = Class: IN (0x0001) >> 1... .... .... .... = Cache flush: True >> Time to live: 4500 (1 hour, 15 minutes) >> Data length: 1 >> TXT Length: 0 >> TXT: >> _http._tcp.local: type PTR, class IN, test._http._tcp.local >> Name: _http._tcp.local >> Type: PTR (domain name PoinTeR) (12) >> .000 0000 0000 0001 = Class: IN (0x0001) >> 0... .... .... .... = Cache flush: False >> Time to live: 4500 (1 hour, 15 minutes) >> Data length: 2 >> Domain Name: test._http._tcp.local >> test._http._tcp.local: type SRV, class IN, cache flush, priority 0, >> weight 0, port 80, target primary.local >> Service: test >> Protocol: _http >> Name: _tcp.local >> Type: SRV (Server Selection) (33) >> .000 0000 0000 0001 = Class: IN (0x0001) >> 1... .... .... .... = Cache flush: True >> Time to live: 120 (2 minutes) >> Data length: 16 >> Priority: 0 >> Weight: 0 >> Port: 80 >> Target: primary.local >> primary.local: type A, class IN, cache flush, addr 192.168.1.1 >> Name: primary.local >> Type: A (Host Address) (1) >> .000 0000 0000 0001 = Class: IN (0x0001) >> 1... .... .... .... = Cache flush: True >> Time to live: 120 (2 minutes) >> Data length: 4 >> Address: 192.168.1.1 >> >> (The below record is optional, it makes it so you can browse what types of >> services exist on the local network) >> _services._dns-sd._udp.local: type PTR, class IN, _http._tcp.local >> Name: _services._dns-sd._udp.local >> Type: PTR (domain name PoinTeR) (12) >> .000 0000 0000 0001 = Class: IN (0x0001) >> 0... .... .... .... = Cache flush: False >> Time to live: 4500 (1 hour, 15 minutes) >> Data length: 2 >> Domain Name: _http._tcp.local >> >> Hope that helps? >> >> Cheers, >> Trent (@lathiat) >>
