I have finally tracked down the source of an annoying packet loss issue that plagues my VPN links between Bangkok and London and between Bangkok and Singapore.
The L2TP/PPTP/OpenVPN (all show same issue) tunnels are set up to service these VPNs using MTU sizes of 1460 and an MRRU value of 1600 so that a tunnel MTU size of 1500 is completely supported. Testing between the two physical IP tunnel endpoint addresses with 1500 byte packets shows no packet loss whilst testing across the tunnels shows a random packet loss component, usually less than 2-3 percent, but sometimes (randomly) much higher. The same test with 1400 byte packets shows no loss or a loss level equal to that between the two physical endpoints.
Testing across EoIP tunnels configured at 1500 bytes MTU show no loss or a loss level equal to that between the two physical endpoints.
Apparently the reassembly algorithm for EoIP can handle out-of-order packets well whilst the algorithm used by MLPPP is unable to cope with the level it is seeing.
I've seen other posts in the past that describe what appears to be the same issue...