VPLS MTU ping timeout

[seko]

Hi

The architechture is as follws:

1) We have a MPLS Core network which is based on the Alcatel‐Lucent 7705 SAR‐8 IP/MPLS router. This is a circular redundant networks.

2) At the control room we have the access switches for L2 Alcatel Lucent OS6450 model equipped with 24 or 48 ports.They support wire rate layer‐2 forwarding, extended L2 bridging and access functionalities.

3) At the ends we have the layer 3 aggregation network which is based on Alcatel‐Lucent 7210 SAS‐M service access switch.

Testing:
Now we have some plc's, modbus gateways etc connected to the 7210's. From the control room we can ping the modbus gateway (https://media.conrad.com/medias/global/ ... S_1000.jpg)

ping 10.14.65.161 -l 1468 -> OK

if a 'bigger' packet is used we get a timeout:
ping 10.14.65.161 -l 1469

We have tried to exchange the modbus gateway with a Fluke network analyzer with similar results -dough it works for the first 1-2 minutes:
While connected to the 7210 with we run:
ping 10.14.65.161 -l 1469 -t -> OK, in the first 1-2 minutes. After this we get a timeout. ping 10.14.65.161 -l 1468 still OK

What can be the issue?