If pinging on the local area network works then the VPN should be addressed. As Brandon mentions in a previous comment you may want to look at http: Passing these checks ensures that MTU works properly along the entire path.NMap 101: Fun With Firewalls! HakTip 102
July 29, 2014 at 6: At the very least, you should document where in your network topology that these MTU size problems may occur so you are ready to quickly troubleshoot any application issues that may result. There's no laws saying people have to follow the relevant standard of the Internet and there are companies who break the standards, usually to be cheap. Keep getting the message; Element not found.
As you can imagine this process is not very efficient and contributes to performance degradation in the long run. What detail symptoms will I be getting if MTU size mismatch? This entry was posted in How-To.
Frames are generated by Layer-2 devices and encapsulate Layer-3 packets. However, what kind of networking issue I should expect as issue if MTU was misconfigurated on some appliance?
If fragmentation takes place after encryption, then the destination tunnel router will need to perform reassembly before it can decrypt the packet which can add CPU overhead. As this blog post will illustrate, connectivity failures caused by this condition can cause an array of operational failures as simple a file copy to RPC connectivity disruptions used by numerous management and distributed operations on Windows computers.
In some situations and operating systems, you might also get an error message telling you if you are getting back ICMP "fragmentation needed" messages or other signs that your MTU is incorrect. Only when you can't clear this up, you should set all NICs to the exact same size and the switches to 22 bytes larger.
These two parameters are important in determining how application streams are split into different packets so that network interfaces across a path can forward them, and end-hosts are able to piece them together, both at the network MTU and transport MSS layers.