RT-AC86U: "PCP MAP: failed to add mapping TCP" error every 15 minutes

[Uluqat]

I am running Merlin's 384.14_2 on my ASUS RT-AC86U and the router log is showing an error every 15 minutes that I don't understand:

Jan 27 14:35:49 miniupnpd[1460]: PCP MAP: failed to add mapping TCP 9->192.168.50.162:9 'PCP MAP 68e9e3fadbd4ca8c3e79352b'
Jan 27 14:50:49 miniupnpd[1460]: PCP MAP: failed to add mapping TCP 9->192.168.50.162:9 'PCP MAP 68e9e3fadbd4ca8c3e79352b'

192.168.50.162 is my Mac Mini running macOS 10.15.2 (Catalina). The only application I have running is Firefox.
I've tried restarting the Mac Mini, and changing the “Enable secure UPnP mode” setting from “Yes” to “No” but the error still occurs. When I change the “Enable UPnP mode” setting from “Yes” to “No”, miniupnpd shuts down and stays shut down and the error stops, but when I re-enable UPnP, the error starts again.

I don't know what my Mac is doing to make these errors happen or how to check, and I don't really understand UPnP very well so I don't know what I am losing by disabling it or if this error matters at all.

 

[ColinTaylor]

Port 9 is typically used for WOL. Are you using that for your Mac Mini?

 

[Uluqat]

Port 9 is typically used for WOL. Are you using that for your Mac Mini?

Didn't think I was using Wake On LAN, certainly have never had any need for it. I had to google how to turn it on in macOS. So I go to System Preferences -> Energy Saver and "Wake for network access" is on. WTF? I have turned it off now.

Thank you!

Edit: After doing that, I hit the "Restore Defaults" button and, among other things, WOL turned back on. Mac users should be aware that this is a default setting. I certainly wasn't.

 

[Uluqat]

After turning off WOL, I rebooted the Mac and rebooted the router, but the error is still occurring.

 

[ColinTaylor]

WOL is usually turned on for most PC/laptops. All my computers have it enabled. That's not a problem in itself because it's something that is only applicable to devices on the local network.

It would only be an issue if someone/something was trying to enable remotely sending WOL packets from the internet to a device on your LAN. Do you have some sort of app that tries to do this?

 

[Uluqat]

No, I don't know of anything like that. Our mobile devices are two iPhones and an iPad, and it seems like we would need to have installed an app specifically to do that, and we have no reason to do that.

 

[ColinTaylor]

OK I've had a search around and I don't think this is anything to do with WOL (which normally uses UDP not TCP).

According to RFC 6887 a client can use PCP on port 9 to obtain the external IP address of a gateway device. This is used for things like updating DDNS addresses.

https://tools.ietf.org/id/draft-boucadair-pcp-flow-examples-04.html#rfc.section.4
https://tools.ietf.org/html/rfc6887#section-11.6

So I suspect this is a fairly benign action but it is creating an error because by default the router is set to not allow mapping of ports <1024. See WAN > Internet Connection > UPNP: Allowed internal port range.

 

[Uluqat]

After some fumbling around until I could force the error to happen, I found some log entries that seem to go with the error. I don't know if they add any useful information.

Jan 28 03:10:44 miniupnpd[7810]: PCP MAP: failed to add mapping TCP 9->192.168.50.162:9 'PCP MAP 26e9b7655f0b7ba17c2f8138'
Jan 28 03:10:44 miniupnpd[7810]: sendto(natpmp): Network is unreachable
Jan 28 03:10:44 miniupnpd[7810]: PCP MAP: failed to add mapping TCP 9->192.168.50.162:9 'PCP MAP e7cdb67956c93909dcd9d423'
Jan 28 03:10:44 miniupnpd[7810]: sendto(pcpserver): Network is unreachable

Jan 28 03:12:35 miniupnpd[8886]: PCP: External IP in request didn't match interface IP
Jan 28 03:12:35 miniupnpd[8886]: PCP MAP: failed to add mapping TCP 9->192.168.50.162:9 'PCP MAP ffe6bf07c8c2e73169bea86c'

Allowing the mapping of ports < 1024 via the Allowed Internal Port Range does stop the error from happening, but no alternative log messages of a successful action occur. I am not going to leave it that way. I tried port forwarding TCP port 9 instead, but that did not stop the error from happening.

 

[ColinTaylor]

I'm not a Mac person, but isn't there some sort of log file on the Mac Mini that you can look at (like the Windows Event Log). That would seem to be the logical place to try and track down the problem.

 

[Uluqat]

I found some log entries on the Mac that matched timestamps with an instance of the error. These 8 entries seemed to be consistent in other instances of the error. The four "private" entries are all the same, and so are the four "Stealth Mode" entries.

 

[ColinTaylor]

Are you running torrents on the Mac Mini?

 

[Uluqat]

I tried turning off Stealth Mode in the Mac's firewall settings, but that didn't fix the error.

However, I think I finally got the right phrase to google: "mdnsresponder pcp map failed". That led me to this thread:

https://superuser.com/questions/1089370/osx-mdnsresponder-opening-all-ports-on-billion

which has a link to this thread:

https://forums.whirlpool.net.au/archive/2180205

The upshot seems to be that this is probably a long-standing bug in the part of macOS's mDNSResponder that does Bonjour.

 

[vaboro]

@Uluqat, I've been ignoring "PCP MAP: failed to add mapping TCP 9" for years. Luckily @RMerlin provides a simple way to solve it with custom config files.
If you find it still useful I added the following upnp.postconf file to /jffs/scripts folder:

Spoiler: /jffs/scripts/upnp.postconf

#!/bin/sh
CONFIG=$1
source /usr/sbin/helper.sh

pc_insert "allow 1-65535 192.168.0.1/255.255.255.0 1024-65535" "allow 1-65535 192.168.0.1/255.255.255.0 9" $CONFIG

The IP/mask and the exact location of the line might be slightly different in your particular case. You might need to look at /etc/upnp/config to find out which IP/mask you have and where to insert the line. Anyways, the line "allow 1-65535 192.168.0.1/255.255.255.0 9" should appear before the final "deny" statement according to miniupnpd developers' recommendations.
And don't forget to make upnp.postconf script executable with # chmod +x upnp.postconf command.