We currently have a IPSec tunnel between a pix 515 in our main office and a 2801 router at our branch office. The tunnel appears to be having fragmentation issues (problems sending large packets through our network), which is causing several of our programs not to work. We have set the MTU size on the outside interface of the PIX to 1400 bytes and we have set the TCP MTU path discovery on the 2801 router. Does the PIX 515 OS ver 6.3 utilize frag guard or some other feature that could be causing this problem?
I have this problem too.