Overview

After organising OpenVPN, we’re capable of join over SSH (e.g. to 10.8.0.9), however the SSH connection hangs/stalls, often after about 2-minutes. The SSH connection is from Ubuntu 18 on WSL to Ubuntu 18 on Digital Ocean.

What have we tried?

• Many recommend that is an MTU drawback, and we have now adjusted the fragment and the mssfix right down to 1200 on all purchasers and servers.
• We’ve got used ping, traceroute, and tracepath to test the MTU between hosts, and the MTU is available in at round 1500.
• We’ve got tried manually to set the tun0 MTU at 1400 with sudo ip hyperlink set dev tun0 mtu 1400 on all of the consumer and server hosts.
• To rule out Firewall causes, we have now briefly disabled the Firewall.

None of that is resolving the stalls/hangs. With all the above adjustments, we are able to nonetheless join over SSH, however inside minutes, the SSH connection hangs/stalls.

Query

We’ve got set our native VPN consumer’s verb to 11. That is the output when the VPN is actively stalling/hanging. What hints, if any, does that output give us about what’s inflicting the hold?

us=52848 UDP write returned 112
us=52924 PO_CTL rwflags=0x0001 ev=5 arg=0x55f0cef4c168
us=53000 PO_CTL rwflags=0x0001 ev=6 arg=0x55f0cef4c068
us=53032 I/O WAIT TR|Tw|SR|Sw [4/92829]
us=91180 PO_WAIT[1,0] fd=6 rev=0x00000001 rwflags=0x0001 arg=0x55f0cef4c068
us=91300  event_wait returned 1
us=91313 I/O WAIT standing=0x0004
us=91325  learn from TUN/TAP returned 84
us=91377 TUN READ [84]
us=91414 FRAG_OUT len=84 kind=Zero seq_id=Zero frag_id=Zero frag_size=Zero flags=0x00000000
us=91427 TLS: tls_pre_encrypt: key_id=0
us=91471 tls_prepend_opcode_v2
us=91503 ENCRYPT IV: 000001ca c1f70e33 9b725bd5
us=91611 ENCRYPT FROM: 00000000 45000054 e8fe4000 40013d85 0a080005 0a080011 080071f2 0c2d000[more...]
us=91677 ENCRYPT AD: 48000008 000001ca
us=91787 ENCRYPT TO: 48000008 000001ca fda00e43 93938a26 d2f6b551 a96d0ced 95ce1caf cb4b087[more...]
us=91899 PO_CTL rwflags=0x0003 ev=5 arg=0x55f0cef4c168
us=91999 PO_CTL rwflags=0x0000 ev=6 arg=0x55f0cef4c068
us=92101 I/O WAIT Tr|Tw|SR|SW [3/92829]
us=92197 PO_WAIT[0,0] fd=5 rev=0x00000004 rwflags=0x0002 arg=0x55f0cef4c168
us=92287  event_wait returned 1
us=92358 I/O WAIT standing=0x0002
us=92525 UDP WRITE [112] to [AF_INET]xxx.xxx.xxx.xxx:1194: P_DATA_V2 child=Zero DATA 00000800 0001cafd a00e4393 938a26d2 f6b551a9 6d0ced95 ce1cafcb 4b0874b[more...]

The hold often lasts for upwards of 5 minutes, throughout which period ping not returns outcomes and SSH is frozen. As soon as the hold resolves itself, each the ping and the SSH connection begin working too.