Again on DNS-SD

[agalliazzo]

Hi Guys,
As I read, Thread network use DNS-SD with SRP to discover devices and services.
That's sounds good: I successfully be able to register a new device in the network updating it's IP address on the SRP server and I can sucesfully resolve the IP from a random PC on my WiFi/Ethernet network (and from my phone).

So, as far as I can understand, SRP registration is sucessfull and mDNS is answering for queries properly from my ethernet network (both the service discover part and the name resolution part).

Now I would like to connect CoAP on device A (that is a router eligible FTD) to device B (that is another router eligible FTD) that has just published itself to the SRP as a _coap._udp capable device. I'm using the C API so, what I was expecting was something like:

	otDnsQueryConfig dns_cfg;
	dns_cfg.mNat64Mode = OT_DNS_NAT64_ALLOW;
	dns_cfg.mRecursionFlag = true;
	memcpy(&dns_cfg.mServerSockAddr.mAddress, &SRP.mAddress, sizeof(otIp6Address));
	dns_cfg.mServerSockAddr.mPort = 5353;
	error = otDnsClientResolveService(NULL, "_coap", "_udp",
			_CP_DNS_Callback, NULL, &dns_cfg);

this partially works, I mean, I can see the packet with wireshark coming in in the otbr but no answer come back. Also no log about the received query.
Am I missing something obvious?

Thanks in advance
Alessio

[jwhui]

It may be that the port is incorrect. Do you have the SRP Client's auto start mode enabled using otSrpClientEnableAutoStartMode ? This should also automatically configure the DNS Client with the proper DNS resolver information. You can then pass NULL for the otDnsQueryConfig.

You can also take a look at the otbr-agent logs on the border router to get more visibility.

[agalliazzo]

No, SRP autostart is disabled. I manualli start it getting the SRP server address from the network data services. I have, indeed, the SRP server address/port is this supposed to be the same of mDNS?
This is my "SRP initialization" function for an STM32WB55 using FreeRTOS:

void _CP_DNS_Callback(otError aError, const otDnsServiceResponse *aResponse, void *aContext){
	aResponse = aResponse;
}

void CP_InitializeSRP() {
	otError error = OT_ERROR_NONE;
	_CP_GetOMR();

	// Registering the local service to the SRP server

	service.mInstanceName = "io";
	service.mName = "_coap._udp";
	service.mPort = OT_DEFAULT_COAP_PORT;
	service.mPriority = 1;
	service.mWeight = 1;
	service.mSubTypeLabels = NULL;
	service.mTxtEntries = NULL;
	service.mNumTxtEntries = 0;

	otServiceConfig conf;
	otNetworkDataIterator it = 0;
	while (conf.mServiceData[0] != 0x5d) {
		error = otNetDataGetNextService(NULL, &it, &conf);
	}
	memcpy(&SRP.mAddress.mFields.m8, &conf.mServerConfig.mServerData, 16);
	SRP.mPort = conf.mServerConfig.mServerData[16] << 8 | conf.mServerConfig.mServerData[17];

	error = otSrpClientSetHostAddresses(NULL, &otLocalMLEIDAddress, 1);
	error = otSrpClientAddService(NULL, &service);
	error = otSrpClientSetHostName(NULL, "TOI2");
	error = otSrpClientStart(NULL, &SRP);

	// Querying the server for a CoAP to MQTT bridge

	otDnsQueryConfig dns_cfg;
	dns_cfg.mNat64Mode = OT_DNS_NAT64_ALLOW;
	dns_cfg.mRecursionFlag = true;
	memcpy(&dns_cfg.mServerSockAddr, &SRP, sizeof(otSockAddr));

	error = otDnsClientResolveService(NULL, "CoAP -> MQTT Bridge", "_coap._udp",
			_CP_DNS_Callback, NULL, &dns_cfg);
}

Yes, this is not bug-proof, it's something written on the fly to test funcionality, is completly lacking proper error checking. I use breakpoint on the callback to check for an answer.

Here you can see the packet from the FTD to the OTBR but no answer back (OTBR address ends in ffcf)

The other thing that sounds strange to me is that avahi-browse for the same query return:

+ veth896278c IPv6 CoAP -> MQTT Bridge                           _coap._udp           local
+ veth896278c IPv4 CoAP -> MQTT Bridge                           _coap._udp           local
+ vethcc66733 IPv6 CoAP -> MQTT Bridge                           _coap._udp           local
+ vethcc66733 IPv4 CoAP -> MQTT Bridge                           _coap._udp           local
+ veth43c6c37 IPv6 CoAP -> MQTT Bridge                           _coap._udp           local
+ veth43c6c37 IPv4 CoAP -> MQTT Bridge                           _coap._udp           local
+ vethfc0a21e IPv6 CoAP -> MQTT Bridge                           _coap._udp           local
+ vethfc0a21e IPv4 CoAP -> MQTT Bridge                           _coap._udp           local
+ vethb843906 IPv6 CoAP -> MQTT Bridge                           _coap._udp           local
+ vethb843906 IPv4 CoAP -> MQTT Bridge                           _coap._udp           local
+ br-f1e6f00def17 IPv4 CoAP -> MQTT Bridge                           _coap._udp           local
+ br-ec6340b43090 IPv6 CoAP -> MQTT Bridge                           _coap._udp           local
+ br-ec6340b43090 IPv4 CoAP -> MQTT Bridge                           _coap._udp           local
+ br-3bc19f48bca1 IPv6 CoAP -> MQTT Bridge                           _coap._udp           local
+ br-3bc19f48bca1 IPv4 CoAP -> MQTT Bridge                           _coap._udp           local
+ docker0 IPv4 CoAP -> MQTT Bridge                           _coap._udp           local
+ br-0878d2f56c42 IPv4 CoAP -> MQTT Bridge                           _coap._udp           local
+   eth0 IPv6 CoAP -> MQTT Bridge                           _coap._udp           local
+   eth0 IPv4 CoAP -> MQTT Bridge                           _coap._udp           local
+     lo IPv4 CoAP -> MQTT Bridge                           _coap._udp           local
= veth896278c IPv6 CoAP -> MQTT Bridge                           _coap._udp           local
   hostname = [thread-4524.local]
   address = [fe80::38ab:3dff:fe4e:af29]
   port = [5683]
   txt = []
= vethcc66733 IPv6 CoAP -> MQTT Bridge                           _coap._udp           local
   hostname = [thread-4524.local]
   address = [fe80::28d2:17ff:feb2:9943]
   port = [5683]
   txt = []
= veth43c6c37 IPv6 CoAP -> MQTT Bridge                           _coap._udp           local
   hostname = [thread-4524.local]
   address = [fe80::383f:1fff:fe7e:f8ad]
   port = [5683]
   txt = []
= vethfc0a21e IPv6 CoAP -> MQTT Bridge                           _coap._udp           local
   hostname = [thread-4524.local]
   address = [fe80::fc91:59ff:fecc:99fd]
   port = [5683]
   txt = []
= vethb843906 IPv6 CoAP -> MQTT Bridge                           _coap._udp           local
   hostname = [thread-4524.local]
   address = [fe80::20dd:d5ff:feb5:e381]
   port = [5683]
   txt = []
= br-ec6340b43090 IPv6 CoAP -> MQTT Bridge                           _coap._udp           local
   hostname = [thread-4524.local]
   address = [fe80::42:6eff:fec7:2b1d]
   port = [5683]
   txt = []
= br-3bc19f48bca1 IPv6 CoAP -> MQTT Bridge                           _coap._udp           local
   hostname = [thread-4524.local]
   address = [fe80::42:8eff:fe01:bc71]
   port = [5683]
   txt = []
=   eth0 IPv6 CoAP -> MQTT Bridge                           _coap._udp           local
   hostname = [thread-4524.local]
   address = [fdfd:fd10:256d:d55f:dea6:32ff:fef8:d9ed]
   port = [5683]
   txt = []
= veth896278c IPv4 CoAP -> MQTT Bridge                           _coap._udp           local
   hostname = [thread-4524.local]
   address = [169.254.133.6]
   port = [5683]
   txt = []
= vethcc66733 IPv4 CoAP -> MQTT Bridge                           _coap._udp           local
   hostname = [thread-4524.local]
   address = [169.254.161.40]
   port = [5683]
   txt = []
= veth43c6c37 IPv4 CoAP -> MQTT Bridge                           _coap._udp           local
   hostname = [thread-4524.local]
   address = [169.254.42.223]
   port = [5683]
   txt = []
= vethfc0a21e IPv4 CoAP -> MQTT Bridge                           _coap._udp           local
   hostname = [thread-4524.local]
   address = [169.254.17.190]
   port = [5683]
   txt = []
= vethb843906 IPv4 CoAP -> MQTT Bridge                           _coap._udp           local
   hostname = [thread-4524.local]
   address = [169.254.86.240]
   port = [5683]
   txt = []
= br-f1e6f00def17 IPv4 CoAP -> MQTT Bridge                           _coap._udp           local
   hostname = [thread-4524.local]
   address = [172.18.0.1]
   port = [5683]
   txt = []
= br-ec6340b43090 IPv4 CoAP -> MQTT Bridge                           _coap._udp           local
   hostname = [thread-4524.local]
   address = [172.23.0.1]
   port = [5683]
   txt = []
= br-3bc19f48bca1 IPv4 CoAP -> MQTT Bridge                           _coap._udp           local
   hostname = [thread-4524.local]
   address = [172.22.0.1]
   port = [5683]
   txt = []
= docker0 IPv4 CoAP -> MQTT Bridge                           _coap._udp           local
   hostname = [thread-4524.local]
   address = [172.17.0.1]
   port = [5683]
   txt = []
= br-0878d2f56c42 IPv4 CoAP -> MQTT Bridge                           _coap._udp           local
   hostname = [thread-4524.local]
   address = [172.19.0.1]
   port = [5683]
   txt = []
=   eth0 IPv4 CoAP -> MQTT Bridge                           _coap._udp           local
   hostname = [thread-4524.local]
   address = [192.168.2.4]
   port = [5683]
   txt = []
=     lo IPv4 CoAP -> MQTT Bridge                           _coap._udp           local
   hostname = [thread-4524.local]
   address = [127.0.0.1]
   port = [5683]
   txt = []

That are all the interfaces on the OTBR but not the WPAN0. Can this be a problem too?

Thanks again for your support! I really appreciate

[agalliazzo]

Ok, I sorted out a couple of problem:

1. Before resolve the name I should had use otDnsClientBrowse to get the list of hostnames
2. The port is not the SRP port but port 53 (as standard in DNS)

For info if someone is searching the same topic:
openthread/ot-br-posix#864 (comment)

I will add a snipped from my code in the next post just to help others with same problems that I encountered :)

Thanks guys for your support!