Commissioner discovery over DNS-SD returns no results

[sharadb-amazon]

Problem

• Expected behavior: tv-casting-app should be able to discover on network commissioners using DNS-SD and list them to the user on startup
• Actual Behavior: tv-casting-app, does NOT discover any commissioners
• Steps to reproduce:

1. Build and run a commissioner that advertises itself over DNS-SD like chip-tv-app
2. Build and run the chip-tv-casting-app
3. Note that the console output on the tv-casting-app's side has a line stating: "CHIP:SVR: No commissioner discovered, commissioning must be initiated manually!" like the one below:

$ ./out/host/chip-tv-casting-app
[1637777886.417526][2375:2375] CHIP:DL: writing settings to file (/tmp/chip_counters.ini-2Kct3K)
[1637777886.420274][2375:2375] CHIP:DL: renamed tmp file to file (/tmp/chip_counters.ini)
[1637777886.420446][2375:2375] CHIP:DL: NVS set: chip-counters/reboot-count = 54 (0x36)
[1637777886.424698][2375:2375] CHIP:DL: Failed to get Ethernet interface
[1637777886.425141][2375:2375] CHIP:DL: Failed to reset Ethernet statistic counts
[1637777886.425390][2375:2375] CHIP:DL: Failed to get WiFi interface
[1637777886.425497][2375:2375] CHIP:DL: Failed to reset WiFi statistic counts
[1637777886.439353][2375:2375] CHIP:DIS: Attempt to mDNS broadcast failed:  ../../third_party/connectedhomeip/src/inet/UDPEndPoint.cpp:1044: OS Error 0x02000065: Network is unreachable
[1637777891.442438][2375:2375] CHIP:SVR: No commissioner discovered, commissioning must be initiated manually!
...
...

A similar issue is observed when using the "chip-tool discover commissioners" command.

Proposed Solution

TBD?

NOTE: This issue started happening after the following commit was made: 7c47bed

[sharadb-amazon]

Also note, in the test above, I ran the chip-tv-app and the chip-tv-casting-app on the same Docker (Ubuntu) instance, in case that is relevant.

[andy31415]

Maybe fixed in #12161 if the error is apps listening on 5353 and conflicting.

When you see the failure, could you run a netstat -a -n -p | grep 5353 and see how many things are listening on that port? Generally there should be only one but my guess is you have several.

[andy31415]

Likely running chip-tv-app and chip-tv-casting-app is the cause (both run on 5353 and conflict). You could use network namespaces to run separate networks for each and then your tests may pass (currently test_suites.sh does this for linux test runs).

[cecille]

I suspect this is related to #11635. Can you confirm

• which mdns implementation is being used (platform or minimal) on both the commissioner and the app?
• what os you're using to run these (both on linux, both on mac, separate devices etc.)
• whether you're running another mdns instance alongside these (avahi, bonjour etc.)

I agree with Andrei - the PR he linked may be the answer here. Another option is to force both to use the platform mdns implementation (chip_mdns="platform")

[sharadb-amazon]

#12161 fixed the issue.