>[оверквотинг удален]
> ip address 192.168.0.1 255.255.255.0
> ip nat inside
> no ip virtual-reassembly
> keepalive 20 3
> tunnel source x.x.x.x
> tunnel destination y.y.y.y
>
>Подскажите кто-нибудь куда копать.
>Буду благодарен за любой совет.
>

Please read this article:

http://www.cisco.com/en/US/tech/tk827/tk369/technologies_tec...

I think that you have some problem with packets with DF bit.
So, set temporary
debug ip icmp on your router

I had a similar problem with IPSec tunnel and
no crypto ipsec df-bit
has resolved the problem.