I have one ASA5520 and one ASA5505 in two different cities A and B, and created site to site vpn between them.
recently the vpn performance became worse and worse, there are 10-20% packages lost when pinging from LAN A to LAN B.
but there is no any problem if ping from 5520 external interface to 5505 external interface.
I have changed a new 5505 and upgraded the software to the same version of 5520, but no luck to solve
and I also tried to disconnected the LAN B, and connected only one laptop on 5505, it's the same.
BTW, i have the same 5505 in city C, and it works perfect.
Could this be the problem of ISP in city B?