I'm having an interesting issue with my VPN connection. My connection is working properly and I'm able to get a decent speed (10 mbps) but the CPU of my router is working heavily when the traffic approches 10 mbps.
VPN Client :
Ubuntu Server 13.04
With: OpenVPN 2.2.1 x86_64-linux-gnu [SSL] [LZO2] [EPOLL] [PKCS11] [eurephia] [MH] [PF_INET6] [IPv6 payload 20110424-2 (2.2RC2)] built on Feb 13 2013
I noticed that the CPU of my router is spiking when "a lot" of traffic is going through the vpn connection. In addition, I receive these syslog from my router:
257: Severity "Warning" in [192.168.XX.XX: 214: Jul 29 15:01:46: %IP_VFR-4-FRAG_TABLE_OVERFLOW: FastEthernet0: the fragment table has reached its maximum threshold 64]
After some research I realized that the packets I receive from the AirVPN gateway are oversize: they are 1517 bytes long (I sniffed my WAN interface to determine this). Bigger than MTU packets explain the CPU spikes and the syslog warning that I receive: my router's cpu cannot reassemble ip packets fast enough.
Just to be clear: the layer 3 payload is of size 1517 bytes. In total the actual size of the data on wire is 1514 + 71 bytes.
What I tried
Clearly there is some sort of issue with the OpenVPN connection. I searched around and I tried different combinaison of the "mssfix" and "fragment XXXX" (I tried fragment 1400) but I'm unable to receive packets smaller than MTU.
Does anyone has any tip on this sort of issue?
Thanks for your help