Error Codes - 6023 and 6024 (Unable To Negotiate A Successful Connection)

This error means something is preventing Parsec from making the network connection between you and the other computer. This peer-to-peer connection could be prevented because of NAT issues, firewall issues, improper/non-existent port forwarding, or even if your ISP has been blocking the UDP connections.

Make sure to check everything below on both of the computers that are trying to make the connection.

Restart the computer and router

Sometimes, simply restarting everything fixes this error. Restart the computer and router on both the host and client having issues.

Allow Parsec on the firewall

Both the host and client should make sure that Parsec is allowed on the firewall. On Windows:

  • Press Windows key + R, paste control firewall.cpl and press Enter
  • Select "Allow an app or feature...." in the sidebar
  • Click Change settings, search for Parsec and enable the checkboxes, then click OK

If you want to be absolutely sure your firewall isn't the culprit, you can also disable it temporarily by selecting "Turn Windows Defender on or off" in the sidebar instead of "Allow an app or feature....", and disabling everything. Make sure to re-enable once you find out that's not it, though, or your PC will be more vulnerable to security issues.

Make sure your home isn't using two routers

If, for example, you purchased your own router and plugged it directly into your internet provider's router to improve the Wi-Fi signal in your house, that can prevent Parsec from making the connection.

If the host or client's home has multiple routers, make sure to connect your device directly to the router that provides internet, most likely the router given by your internet provider that plugs into the wall outlet (either cable, fibre, or DSL). If you cannot do that, you can alternatively search online how to change the other router's settings into something called either access point or bridge mode.

Check if you're behind a carrier-grade NAT

A carrier-grade NAT is a part of your internet provider's infrastructure. It is very common, and if both the host and client have it, Parsec cannot make the connection. You should check if you and your friend is behind a carrier-grade NAT with the instructions below.

If you're behind a carrier-grade NAT, you can request a public static IP from your internet provider. It's often free or inexpensive to get, and if you want to use Parsec often, it's the way to go. With only one person behind a carrier-grade NAT, Parsec should be able to make the connection just fine.

If both people are behind a carrier-grade NAT, and you can't solve it with your internet providers, Parsec won't be able to make the connection and you'll need to use the P2P VPN provided at the end of this article to bypass this limitation.

How to check if I'm behind a carrier-grade NAT?

Check with the steps below:

  • Press Windows key + R
  • Paste this onto the new window: cmd /k tracert
  • Press Enter. A new black window will show up
  • Wait for a while until it shows 'Trace complete.' You'll see a list of IPs in the window


Check if any of the IPs in the black window (except the first IP) are in this list:

    • to
    • to
    • to
    • to

If you see any that are in the list, that is bad news, you're potentially behind a carrier-grade NAT. The exception is if the IP you saw has the exact first 3 sets of numbers as the first IP in your black window, which means it can be safely ignored (for example, and

Configure your router

If you ensured you don't have any of the issues listed beforehand, you can try configuring your router below. If you're behind a carrier-grade NAT, configuring the router will not fix your issue, and you should look into using a P2P VPN listed at the end of the article instead.

How to port-forward Parsec

Solutions for people using pfSense or OPNsense

If you're trying to connect, but you use pfSense or OPNsense at home as your gateway/firewall, you might need to set Hybrid NAT rules, with a rule pointing to your local IP (having a static DHCP lease helps here).

Use ZeroTier

If everything else in this article has been looked into but did not help, follow this tutorial on using the ZeroTier P2P VPN.

This is not a guaranteed fix, and you may have issues with it even if it works, but it's the only option left if everything else has failed to resolve the error.