Media for DECnet over GRE tunnel with FiberOptic leased-line

Hi All,

I have a problem in tunneling DECNET traffic over GRE using FiberOptic leased-line as the media in the middle of the network.

DECNET terminal - router - layer3 switch - FiberOptic - layer3 switch - router - DECNET server

Although the DECNET packet is smaller the link mtu, I guess, I've try to enable tunnel PMTUD (tunnel path-mtu-discovery) and configure ip mtu

1476 in the tunnel interface.

Then I tried to modify the DF-bit using ip policy route-map in the tunnel interface. It still doesn't work.

Has anyone ever experience this problem?

Does it have something to do with the GRE Tunnel latency?

Regards, Sali