In my case, I have two Cisco ASA5505 firewall vpn. They create a ipsec site to site tunnel. I want to use this tunnel to transfer data.

When I try to make a ping testing. The reply is timeout.

For example:

I use ping -l 65500 xxx.xxx.xxx.xxx bytes packet for ping testing.

It's reply is request timeout. But I use ping -l 17500 xxx.xxx.xxx.xxx bytes packet.

It has normal reply. When it over 17500 bytes packet size. The ping request is timeout.