PPP LFI over L2TPv3

Hi all,

PPP LFI (link fragmentaion and interleaving) over L2TPv3 - is it possible? Could anybody implement this with Cisco routers?

The problem is the following. We have a central office with Cisco3660 and some remote offices with, say, Cisco 871s. The remote offices are connected to the central one through the provider's network, which has a mixed nature - somewhere FR, somewhere Wi-Fi, somewhere plain ethernet. Traditionally I used GRE-tunnels (encrypted with IPSEC) to pass the traffic between the offices. This worked and keeps working now.

But then, the following idea to improve VoIP quaulity in this VPN has appeared. What if I replace GRE-tunnels with L2TPv3 ones, pass PPP over L2TPv3, and the cut the traffic to the small pieces using multilink PPP interleaving and fragmentation.

I have made the working model on my LAN and everything seemed to work. But it only seemed, unfortunately. Pings walked through the tunnel, but the other traffic (HTTP etc) could not. After more detailed investigation it became clear that IP-packets bigger than the PPP fragment could not pass the tunnel. Probably the fragments could not be reassembled on the tunnel's far end. When I tried to turn interleaving off, all began to work. But I don't need the tunnel without interleaving - I would better use plain old GRE in this case.

So the question is: what is wrong? Have not Cisco routers learned to pass fragmented PPP over L2TPv3 pseudwires yet or is there something wrong with my hands? If anybody managed to implement this schema, I could show my configs for more detailed investigation.

Thanks in advance.

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