You can make a difference in the Apple Support Community!

When you sign up with your Apple Account, you can provide valuable feedback to other community members by upvoting helpful replies and User Tips.

Looks like no one’s replied in a while. To start the conversation again, simply ask a new question.

Old iMac Keeps Taking Port 4500 via UPnP

I have an old iMac running Snow Leopard and it's got a very annoying problem. Every time it boots up, it grabs UDP port 4500 via UPnP from my DD-WRT router. Problem is, I have a Mac Mini running a VPN server and when the iMac takes that port, the VPN no longer works. I think it also grabs the port when it wakes from sleep.


lsof output (Run on the iMac. Note the lack of 4500.)

lsof -Pi

COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME

SystemUIS 126 roberthsr 6u IPv4 0x07094734 0t0 UDP *:*

SystemUIS 126 roberthsr 10u IPv4 0x08067aa4 0t0 UDP *:*

AppleVNCS 142 roberthsr 8u IPv6 0x06adcf80 0t0 TCP *:5900 (LISTEN)

sshd 191 roberthsr 3u IPv4 0x06adfad8 0t0 TCP imacg5.socamx.net:22->rmbp.socamx.net:62816 (ESTABLISHED)

sshd 191 roberthsr 4u IPv4 0x06adfad8 0t0 TCP imacg5.socamx.net:22->rmbp.socamx.net:62816 (ESTABLISHED)


nmap output (Scanning the iMac from my laptop. Note that it is listening on 4500.):

sudo nmap -sU -T5 -p 500,1701,4500,9999 10.0.10.6

Starting Nmap 6.49BETA4 ( https://nmap.org ) at 2015-07-16 11:20 EDT

Nmap scan report for (10.0.10.6)

Host is up (0.0019s latency).

PORT STATE SERVICE

500/udp open|filtered isakmp

1701/udp closed L2TP

4500/udp open|filtered nat-t-ike

9999/udp closed distinct

MAC Address: 00:1B:63:16:17:0B (Apple)


Nmap done: 1 IP address (1 host up) scanned in 1.27 seconds


How can I make this iMac stop taking port 4500 and thus prevent it from breaking my VPN? This has been driving me nuts for months. I just want the stupid thing to stop grabbing UDP 4500 via UPnP. Turning off UPnP on the router is not an option. Running newer than 10.6 / Snow Leopard isn't an option either, this computer exists for Rosetta functionality.



As a side note, all my other Macs used to do this too but I disabled Back to My Mac on each of them to stop it. This old iMac running Snow Leopard, I can't access that setting because it is pre-iCloud. It's just an inaccessible MobileMe section in System Preferences, which is obviously long outdated.

Posted on Jul 16, 2015 8:26 AM

Reply
Question marked as Top-ranking reply

Posted on Jul 19, 2015 6:34 AM

I may have got the problem solved. Going to give it a day to be absolutely certain but initially it looks successful.


So because there's no way to access the MobileMe panel anymore, I found out that you can manually remove the Back to my Mac information in a preference file, specifically this one:


/Library/Preferences/SystemConfiguration/preferences.plist


Way down in the file there's a section that looks like this.


<key>Network</key>

<dict>

<key>BackToMyMac</key>

<dict/>

<key>HostNames</key>

<dict>

<key>LocalHostName</key>

<string>ComputerNameHere</string>

</dict>

</dict>


I had to edit my file to make it look similar to that. You need to remove the <dict></dict> section below <key>BackToMyMac</key> and change it to <dict/> This section contains your iCloud username, and upon removing it and restarting the computer, it should no longer grab port 4500 over UPnP.


If this problem goes away forever, I will not update this thread anymore.

1 reply
Sort By: 
Question marked as Top-ranking reply

Jul 19, 2015 6:34 AM in response to Justin Hunter

I may have got the problem solved. Going to give it a day to be absolutely certain but initially it looks successful.


So because there's no way to access the MobileMe panel anymore, I found out that you can manually remove the Back to my Mac information in a preference file, specifically this one:


/Library/Preferences/SystemConfiguration/preferences.plist


Way down in the file there's a section that looks like this.


<key>Network</key>

<dict>

<key>BackToMyMac</key>

<dict/>

<key>HostNames</key>

<dict>

<key>LocalHostName</key>

<string>ComputerNameHere</string>

</dict>

</dict>


I had to edit my file to make it look similar to that. You need to remove the <dict></dict> section below <key>BackToMyMac</key> and change it to <dict/> This section contains your iCloud username, and upon removing it and restarting the computer, it should no longer grab port 4500 over UPnP.


If this problem goes away forever, I will not update this thread anymore.

Reply

Old iMac Keeps Taking Port 4500 via UPnP

Welcome to Apple Support Community
A forum where Apple customers help each other with their products. Get started with your Apple Account.