Community discussions

MUM Europe 2020
just joined
Topic Author
Posts: 2
Joined: Thu Nov 28, 2019 8:59 pm

Packets loss in L2TP/IPSec tunnel

Tue Jan 14, 2020 9:34 pm


I have site-to-site L2TP/IPSec connection between CCR1009 over high-latency link (200ms)
both running 6.46.1
one side has 30M/30M connection, another one 300M/15M.

SMB/FTP Speed is pretty bad across this tunnel, so I decided to debug it:
I've set up packet capture on both CCRs and ran bandwidth test limited to 1mbit (to make sure that channel saturation is not a factor) from machine in one subnet to machine in another one.
basically I have sniffers on both ends of tunnel.

In capture results I can see packets that enter tunnel on one side, but never exit another, thus triggering "fast retransmission". Nothing is fast about it though, due to high latency.
tx/rx errors/drops on both sides of tunnel don't increase.
Number of packets lost is pretty small: approx 10 out of 10000, or 10 per 60 secs.

Also I observe out of order packets time to time, which is not as bad, but still suspicious.
I am not sure either of this may cause speed problems, but fast retransmits definitely affect wnd size.

1) is it normal to have packets reordered while in tunnel?
2) is it normal for tunnel to drop packets quietly?
3) any typical suspects in settings to look at?


Who is online

Users browsing this forum: bgpro, Bing [Bot], marisspringis, MarkoB, quackyo, srsgroupsro and 117 guests