MTU Problem + Openvpn

[sledge121]

Pinging from the box with a frame size of 85 or over fails, I've noticed this on a number of boxes.

root@vuduo:~# ping -s 84 8.8.8.8
PING 8.8.8.8 (8.8.8.8): 84 data bytes
72 bytes from 8.8.8.8: seq=0 ttl=47 time=28.786 ms
72 bytes from 8.8.8.8: seq=1 ttl=47 time=31.167 ms
72 bytes from 8.8.8.8: seq=2 ttl=47 time=27.368 ms
^C

root@vuduo:~# ping -s 85 8.8.8.8
PING 8.8.8.8 (8.8.8.8): 85 data bytes
^C
--- 8.8.8.8 ping statistics ---
19 packets transmitted, 0 packets received, 100% packet loss

This also appears to be causing the following errors

Nov 7 10:15:32 vusolo daemon.err openvpn[354]: read UDPv4 [EMSGSIZE Path-MTU=1432]: Message too long (code=97)
Nov 7 10:15:36 vusolo daemon.err openvpn[354]: read UDPv4 [EMSGSIZE Path-MTU=1432]: Message too long (code=97)
Nov 7 10:15:44 vusolo daemon.err openvpn[354]: read UDPv4 [EMSGSIZE Path-MTU=1432]: Message too long (code=97)
Nov 7 10:15:54 vusolo daemon.err openvpn[354]: read UDPv4 [EMSGSIZE Path-MTU=1432]: Message too long (code=97)

 

[sledge121]

I fixed the openvpn issue (which is unrelated) by adding a lower value in the config file using the link-mtu directive, looks like either the wifi interface or the talk talk dsl router has a lower than 1500 mtu, still doesnt explain why outbound I cant go over 85 bytes

 

[sledge121]

Guys, is the ping failure of 85 bytes and over by design, looks like its the same on different box types.

Thanks
Sledge

 

[mickyblueys]

I fixed the openvpn issue (which is unrelated) by adding a lower value in the config file using the link-mtu directive, looks like either the wifi interface or the talk talk dsl router has a lower than 1500 mtu, still doesnt explain why outbound I cant go over 85 bytes

I have talk talk DSL router and my MTU is 1500, no problems.

Sent from my GT-I9100 using Tapatalk 2

 

[sledge121]

Try an outbound ping over 85 bytes

 

[sledge121]

No takers on this one?

 

[cupra.john]

Same on mine i'm not using open vpn (just about to) but it seems like its only google dns where i get odd results

Welcome to ViX for et9x00
ViX v2.4
et9x00 login: root
root@et9x00:~# ping -s 100 8.8.8.8
PING 8.8.8.8 (8.8.8.8): 100 data bytes
^C
--- 8.8.8.8 ping statistics ---
26 packets transmitted, 0 packets received, 100% packet loss
root@et9x00:~# ping -s 84 8.8.8.8
PING 8.8.8.8 (8.8.8.8): 84 data bytes
72 bytes from 8.8.8.8: seq=0 ttl=50 time=43.888 ms
72 bytes from 8.8.8.8: seq=1 ttl=50 time=37.571 ms
72 bytes from 8.8.8.8: seq=2 ttl=50 time=37.171 ms
72 bytes from 8.8.8.8: seq=3 ttl=50 time=36.845 ms
72 bytes from 8.8.8.8: seq=4 ttl=50 time=37.189 ms
72 bytes from 8.8.8.8: seq=5 ttl=50 time=37.834 ms
72 bytes from 8.8.8.8: seq=6 ttl=50 time=37.459 ms
72 bytes from 8.8.8.8: seq=7 ttl=50 time=37.357 ms
72 bytes from 8.8.8.8: seq=8 ttl=50 time=36.766 ms
72 bytes from 8.8.8.8: seq=9 ttl=50 time=37.316 ms
72 bytes from 8.8.8.8: seq=10 ttl=50 time=37.777 ms
^C
--- 8.8.8.8 ping statistics ---
11 packets transmitted, 11 packets received, 0% packet loss
round-trip min/avg/max = 36.766/37.924/43.888 ms
root@et9x00:~# ping -s 85 8.8.8.8
PING 8.8.8.8 (8.8.8.8): 85 data bytes
^C
--- 8.8.8.8 ping statistics ---
21 packets transmitted, 0 packets received, 100% packet loss
root@et9x00:~#

this is a ntp server that works fine

root@et9x00:~# ping -s 1000 194.117.152.85
PING 194.117.152.85 (194.117.152.85): 1000 data bytes
1008 bytes from 194.117.152.85: seq=0 ttl=56 time=59.436 ms
1008 bytes from 194.117.152.85: seq=1 ttl=56 time=53.795 ms
1008 bytes from 194.117.152.85: seq=2 ttl=56 time=51.776 ms
1008 bytes from 194.117.152.85: seq=3 ttl=56 time=48.560 ms
1008 bytes from 194.117.152.85: seq=4 ttl=56 time=50.387 ms
^C
--- 194.117.152.85 ping statistics ---
5 packets transmitted, 5 packets received, 0% packet loss
round-trip min/avg/max = 48.560/52.790/59.436 ms
root@et9x00:~#

John