Server unreachable from Plex Web, but fine from "Plex for Mac"

Plex Players
21

Server is running on a QNAP NAS.

22

As a follow-up to my question above, the reason I was curious about your client’s ability to resolve your local plex.direct FQDN is that that’s the location where (or at least one of) it will attempt to reach your server.

When you browse to https://app.plex.tv and the web client is loaded, it will retrieve a list of servers to which your account has access and attempt to contact them. To implement secure connections, Plex utilizes a unique FQDN for each server, comprising the parts I listed above.

Once the client knows where it should be able to reach your server, it will attempt to resolve that FQDN to an IP address. A tcpdump of that request will look something like this (taken from a tcpdump on my macOS Safari client browsing to app.plex.tv):

15:40:09.901685 IP (tos 0x0, ttl 255, id 53377, offset 0, flags [none], proto UDP (17), length 102, bad cksum 0 (->d65a)!)
    10.10.0.101.52584 > pihole.domain: [bad udp cksum 0x150e -> 0xecfd!] 39240+ A? 10-10-0-218.redacted.plex.direct. (74)

A successful reply would look something like:

15:40:09.903310 IP (tos 0x0, ttl 64, id 20604, offset 0, flags [DF], proto UDP (17), length 118)
    pihole.domain > 10.10.0.101.52584: [udp sum ok] 39240 q: A? 10-10-0-218.redacted.plex.direct. 1/0/0 10-10-0-218.redacted.plex.direct. [38m41s] A 10.10.0.218 (90)

In this case, the client successfully resolved my server’s plex.direct FQDN to 10.10.0.218. Some DNS servers don’t allow such lookups to be resolved to local IP addresses; this feature is called DNS rebinding protection. It is intended to provide protection from certain types of security attacks.

If the client is unable to resolve the server’s local plex.direct FQDN to an IP address local, secure connections may not be available. This could be the cause of the behavior you’re seeing.

If it is the cause, you may be able to work around the issue by configuring your client to use a DNS server which doesn’t enforce DNS rebinding protection. For example, Google (8.8.8.8) or CloudFlare (1.1.1.1) do not.

1 Like
23

@philipsw I appreciate this info and will have a go tomorrow :slight_smile:

24

I assuming you know there was a new Safari 14.0.2 release 12/14? Was it working before and after that assuming you upgraded it?

Good luck.

25

You assume correctly and yes, it was.

26

that gave me this instead of the logs:

[
  {
    "type": "info",
    "host": "app.plex.tv",
    "userAgent": "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_6) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/14.0.2 Safari/605.1.15",
    "browser": {
      "platformVersion": "10.15",
      "id": "safari",
      "name": "Safari",
      "version": "14.0",
      "webkit": true,
      "platform": "OSX",
      "platformID": "osx",
      "platformModifierKey": "command"
    },
    "version": "4.50.1",
    "username": "JCHH",
    "cloudUrl": [
      {
        "scheme": "https",
        "address": "plex.tv",
        "uri": "https://plex.tv",
        "testState": "untested",
        "isBundled": false,
        "isFallback": false,
        "relay": false,
        "isUntested": true,
        "isPending": false,
        "isConnected": false,
        "isUnauthorized": false,
        "isUnavailable": false,
        "isFailed": false,
        "isAborted": false,
        "isLoopback": false,
        "isPrivate": false,
        "isHttps": true,
        "isSecure": true,
        "isPlexDirect": false,
        "sources": [
          {
            "id": "internal"
          }
        ]
      }
    ]
  }
]

FRI - It’s reporting my OS and Safari versions incorrectly (which are 11.1 and 14.0.2 respectively).

27

Well, that got me thinking. I had already restarted Plex, but not the NAS itself. SO I restarted the NAS and https://app.plex.tv/desktop works again.

Apologies to everyone for wasting their time on this - I should have restarted the NAS before asking you guys for help.

This still outputs the same info as before - is that what you were expecting?

1 Like
28

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