Local Office: RB751 v5.24

Remote Office: CCR1016-12G 6.4

With, or without Encryption, I am consistently getting 20% packet loss through an l2tp tunnel between these devices.
To test, I am using a linux box, and sending 10000 packets at 5ms intervals.

Pinging the external interface of the CCR (no tunnel), results in 0% packet loss.

Allowing access via Firewall rules to a protected server, and pinging it (no tunnel) results in 0% packet loss.

Pinging ANYTHING, including the CCR's l2tp interface IP (via tunnel), results in 20% packet loss.

The remote office was initially at v6.5. I downgraded to 6.4 to see if it would resolve the issue. There was no change.

WHY?!!!


Edit: I have checked the MTU / MRU they were both set at 1460. I tried altering with local at 1420/1420 and remote at 1420(MTU) 1460(MRU). I could not set remote MRU lower, because other tunnels exist - and it would disrupt them. Other tunnels are having problems with VoIP voice quality as well, but I have not been able to perform the same test on them. I am assuming they are experiencing the same issue - but it is not 100% confirmed.

Altering the MTU/MRU did not affect the packet loss.

What happens if you ping with a higher interval? Considering a packet lost after 5ms?
It takes time to encapsulate into l2tp and send it down a tunnel, add some time for that?

Try it at 15ms.

Taking time to encapsulate would result in higher latency, not packet loss. I have previously been able to run six concurrent tests at 5ms with 0% packet loss.

Good thought though...and thanks for responding!


That being said, the problem is not resolved - although I don't have a full root-cause analysis. It was a separate CCR running v6.4 causing the problem. The core router at the datacenter, between the local (home office) and remote (datacenter rack) is a CCR and was running v6.4 of RouterOS. It decided to start doing very strange things, like passing some traffic but dropping others. Among other things, it would drop 20% of l2tp encapsulated traffic that passed through it.

Rebooting the router did not resolve the problem. Doing a system downgrade to 6.2 did.

That's all we know at this point, and all we may ever know. 6.4 fell apart on itself, and the only remedy we could find was a system downgrade to 6.2.

I'm back to 0% packet loss and crystal clear voice quality again.

Im having the same problem today.. its working fine with SSTP tunnel but with L2TP ill get 20% packet loss.
It started a year ago.. no news!?

I have this issue and it's somehow fixed when i disable fast path in bridge settings. But i can't figure out root of this issue.
UPD:
After all this issue was fixed for me when i lowered MTU of L2TP connection on client from 1450 to 1404 (i determined this value using mturoute utility)