It's a little late to reply to the OP, but the MTU is always 1524, as that value is forced upon the Routerboard from the LNS.
I guess you are using Cisco equipment to terminate the MLPPP connection, as 1524 is the Cisco default
value for MLPPP. You should be able to change it on your LNS; but not the fact that this value is always
going to override the settings on the Routerboard.
Regarding your problem - can you please give some more detail on configuration and devices used?
We provide RB750's to our customers who want to use multi-link with us. They are usually set up with 2-4 modems. Depending on the customer needs they will get a dynamic IP, static IP or a static IP with a /29 subnet routed to it. We have started using a MTU/MRU of 1454 as some of the sessions may pass through a L2TP tunnel at some point.
I usually setup port 1 as the "LAN" port which connects to the customers network. Ports 2-5 are for DSL modems. Each of these ports are set to not have a master port. NAT is used on dynamic and static IP's, but turned off when the customer is given a subnet and routes are installed as needed.
In all cases performance is good and the Rx Drops and Rx Errors keeping going up and I'm not sure why. I suspect re-ordering (which is fine) but want to be sure.
Attached to this post is a sample configuration. Also http://pastebin.com/rNr7xND2
just in case.
Thanks for the help.
Modems we use: http://www.zhone.com/products/6511-A1/
You do not have the required permissions to view the files attached to this post.