OpenVPN stopped working, no obvious cause

craiggraham

I've a server running OpenVPN and a few laptops connected to it. Worked fine for months. Last week I changed the server the clients were pointing at from a Linux box to a Windows server, onto which I copied all the config and key files a couple of months ago and got working in a test environment. Changed the openVPN address in DNS to point to the new machine. Worked. Things seemed OK. Files that were changed from clients were confirmed changed on the Windows box, not on the Linux box.

A week later, none of the clients are functioning. They're connecting, but failing to set up the tunnel, or if they do they're not sending traffic over it. Failures differ- the fact it's not the same deterministic set of messages and the same error every time I try to start OpenVPN in a command prompt on my laptop has some significance I think, but I don't know what. It may just be a holdoff period that I recall seeing mention of. And the fact two laptops definitely worked last week and now don't work suggests to me that the issue lies on the server.

The error message in the client log pointed me to a FAQ entry which suggested resetting the TCP/IP stack. Did this on the server. Disabled the server firewall, and the firewall on my laptop. Rebooted both server and laptop. Considered that the issue might be something to do with wifi vs wired networking on the laptop and tried both interfaces. I've not done anything to config files or keys because things were working last week so that'd just risk breaking things further.

I've discovered I'm running different versions, but they were working so I've not tried updating anything yet on the basis that something else is causing this.

I do have good connectivity between client and server- they're both on the same LAN and the client config file is pointing at the local address of the server.

Does anyone have an idea as to what could be going on and how to fix?

Versions:
Client is

OpenVPN 2.4.2 x86_64-w64-mingw32 [SSL (OpenSSL)] [LZO] [LZ4] [PKCS11] [AEAD] built on May 11 2017
library versions: OpenSSL 1.0.2k  26 Jan 2017, LZO 2.10
Windows version 6.1 (Windows 7) 64bit
Originally developed by James Yonan
Copyright (C) 2002-2017 OpenVPN Technologies, Inc. <[email address removed]>
Compile time defines: enable_async_push=no enable_comp_stub=no enable_crypto=yes enable_crypto_ofb_cfb=yes enable_debug=yes enable_def_auth=yes enable_dlopen=unknown enable_dlopen_
self=unknown enable_dlopen_self_static=unknown enable_fast_install=needless enable_fragment=yes enable_iproute2=no enable_libtool_lock=yes enable_lz4=yes enable_lzo=yes enable_mana
gement=yes enable_multi=yes enable_multihome=yes enable_pam_dlopen=no enable_pedantic=no enable_pf=yes enable_pkcs11=yes enable_plugin_auth_pam=no enable_plugin_down_root=no enable
_plugins=yes enable_port_share=yes enable_selinux=no enable_server=yes enable_shared=yes enable_shared_with_static_runtimes=yes enable_small=no enable_static=yes enable_strict=no e
nable_strict_options=no enable_systemd=no enable_werror=no enable_win32_dll=yes enable_x509_alt_username=no with_crypto_library=openssl with_gnu_ld=yes with_mem_check=no with_speci
al_build= with_sysroot=no

Server is

OpenVPN 2.4.4 x86_64-w64-mingw32 [SSL (OpenSSL)] [LZO] [LZ4] [PKCS11] [AEAD] built on Sep 26 2017
library versions: OpenSSL 1.0.2l  25 May 2017, LZO 2.10
Windows version 6.1 (Windows 7) 64bit
Originally developed by James Yonan
Copyright (C) 2002-2017 OpenVPN Technologies, Inc. <[email address removed]>
Compile time defines: enable_async_push=no enable_comp_stub=no enable_crypto=yes
enable_crypto_ofb_cfb=yes enable_debug=yes enable_def_auth=yes enable_dlopen=un
known enable_dlopen_self=unknown enable_dlopen_self_static=unknown enable_fast_i
nstall=needless enable_fragment=yes enable_iproute2=no enable_libtool_lock=yes e
nable_lz4=yes enable_lzo=yes enable_management=yes enable_multihome=yes enable_p
am_dlopen=no enable_pedantic=no enable_pf=yes enable_pkcs11=yes enable_plugin_au
th_pam=no enable_plugin_down_root=no enable_plugins=yes enable_port_share=yes en
able_selinux=no enable_server=yes enable_shared=yes enable_shared_with_static_ru
ntimes=yes enable_small=no enable_static=yes enable_strict=no enable_strict_opti
ons=no enable_systemd=no enable_werror=no enable_win32_dll=yes enable_x509_alt_u
sername=no with_crypto_library=openssl with_gnu_ld=yes with_mem_check=no with_sp
ecial_build= with_sysroot=no

Log files:

Client showing the usual failure mode

Wed Apr 25 15:03:11 2018 OpenVPN 2.4.2 x86_64-w64-mingw32 [SSL (OpenSSL)] [LZO] [LZ4] [PKCS11] [AEAD] built on May 11 2017
Wed Apr 25 15:03:11 2018 Windows version 6.1 (Windows 7) 64bit
Wed Apr 25 15:03:11 2018 library versions: OpenSSL 1.0.2k  26 Jan 2017, LZO 2.10
Wed Apr 25 15:03:11 2018 Outgoing Control Channel Authentication: Using 160 bit message hash 'SHA1' for HMAC authentication
Wed Apr 25 15:03:11 2018 Incoming Control Channel Authentication: Using 160 bit message hash 'SHA1' for HMAC authentication
Wed Apr 25 15:03:11 2018 TCP/UDP: Preserving recently used remote address: [AF_INET]192.168.8.2:1194
Wed Apr 25 15:03:11 2018 Socket Buffers: R=[8192->8192] S=[8192->8192]
Wed Apr 25 15:03:11 2018 UDP link local: (not bound)
Wed Apr 25 15:03:11 2018 UDP link remote: [AF_INET]192.168.8.2:1194
Wed Apr 25 15:03:11 2018 TLS: Initial packet from [AF_INET]192.168.8.2:1194, sid=d73e22d6 8738bdf4
Wed Apr 25 15:03:11 2018 VERIFY OK: depth=1, C=UK, ST=Manchester, L=Manchester, O=AAITechnologies, OU=changeme, CN=AAITechnologies, emailAddress=[email address removed]
Wed Apr 25 15:03:11 2018 VERIFY KU OK
Wed Apr 25 15:03:11 2018 Validating certificate extended key usage
Wed Apr 25 15:03:11 2018 ++ Certificate has EKU (str) TLS Web Server Authentication, expects TLS Web Server Authentication
Wed Apr 25 15:03:11 2018 VERIFY EKU OK
Wed Apr 25 15:03:11 2018 VERIFY OK: depth=0, C=UK, ST=Manchester, L=Manchester, O=AAITechnologies, OU=changeme, CN=AAITechnologies, emailAddress=[email address removed]
Wed Apr 25 15:03:11 2018 Control Channel: TLSv1.2, cipher TLSv1/SSLv3 ECDHE-RSA-AES256-GCM-SHA384, 1024 bit RSA
Wed Apr 25 15:03:11 2018 [AAITechnologies] Peer Connection Initiated with [AF_INET]192.168.8.2:1194
Wed Apr 25 15:03:12 2018 SENT CONTROL [AAITechnologies]: 'PUSH_REQUEST' (status=1)
Wed Apr 25 15:03:12 2018 PUSH: Received control message: 'PUSH_REPLY,explicit-exit-notify 3,route 10.8.0.1,topology net30,ping 10,ping-restart 120,ifconfig 10.8.0.50 1
-id 0,cipher AES-256-GCM'
Wed Apr 25 15:03:12 2018 Option 'explicit-exit-notify' in [PUSH-OPTIONS]:1 is ignored by previous <connection> blocks
Wed Apr 25 15:03:12 2018 OPTIONS IMPORT: timers and/or timeouts modified
Wed Apr 25 15:03:12 2018 OPTIONS IMPORT: explicit notify parm(s) modified
Wed Apr 25 15:03:12 2018 OPTIONS IMPORT: --ifconfig/up options modified
Wed Apr 25 15:03:12 2018 OPTIONS IMPORT: route options modified
Wed Apr 25 15:03:12 2018 OPTIONS IMPORT: peer-id set
Wed Apr 25 15:03:12 2018 OPTIONS IMPORT: adjusting link_mtu to 1625
Wed Apr 25 15:03:12 2018 OPTIONS IMPORT: data channel crypto options modified
Wed Apr 25 15:03:12 2018 Data Channel Encrypt: Cipher 'AES-256-GCM' initialized with 256 bit key
Wed Apr 25 15:03:12 2018 Data Channel Decrypt: Cipher 'AES-256-GCM' initialized with 256 bit key
Wed Apr 25 15:03:12 2018 interactive service msg_channel=0
Wed Apr 25 15:03:12 2018 ROUTE_GATEWAY 192.168.8.254/255.255.255.0 I=11 HWADDR=00:26:b9:b5:d3:a8
Wed Apr 25 15:03:12 2018 open_tun
Wed Apr 25 15:03:12 2018 CreateFile failed on TAP device: \\.\Global\{13C2EDD1-2B6D-4CDF-B435-143C47E95362}.tap
Wed Apr 25 15:03:12 2018 TAP-WIN32 device [Local Area Connection 3] opened: \\.\Global\{2EFEFEDF-8493-411F-A6B9-BE0FA1CDD5C1}.tap
Wed Apr 25 15:03:12 2018 TAP-Windows Driver Version 9.21
Wed Apr 25 15:03:12 2018 Notified TAP-Windows driver to set a DHCP IP/netmask of 10.8.0.50/255.255.255.252 on interface {2EFEFEDF-8493-411F-A6B9-BE0FA1CDD5C1} [DHCP-se
, lease-time: 31536000]
Wed Apr 25 15:03:12 2018 Successful ARP Flush on interface [21] {2EFEFEDF-8493-411F-A6B9-BE0FA1CDD5C1}
Wed Apr 25 15:03:12 2018 do_ifconfig, tt->did_ifconfig_ipv6_setup=0
Wed Apr 25 15:03:17 2018 TEST ROUTES: 0/0 succeeded len=-1 ret=0 a=0 u/d=down
Wed Apr 25 15:03:17 2018 Route: Waiting for TUN/TAP interface to come up...
Wed Apr 25 15:03:22 2018 TEST ROUTES: 0/0 succeeded len=-1 ret=0 a=0 u/d=down
Wed Apr 25 15:03:22 2018 Route: Waiting for TUN/TAP interface to come up...
Wed Apr 25 15:03:23 2018 TEST ROUTES: 0/0 succeeded len=-1 ret=0 a=0 u/d=down
Wed Apr 25 15:03:23 2018 Route: Waiting for TUN/TAP interface to come up...
Wed Apr 25 15:03:24 2018 TEST ROUTES: 0/0 succeeded len=-1 ret=0 a=0 u/d=down
Wed Apr 25 15:03:24 2018 Route: Waiting for TUN/TAP interface to come up...
Wed Apr 25 15:03:25 2018 TEST ROUTES: 0/0 succeeded len=-1 ret=0 a=0 u/d=down
Wed Apr 25 15:03:25 2018 Route: Waiting for TUN/TAP interface to come up...
Wed Apr 25 15:03:26 2018 TEST ROUTES: 0/0 succeeded len=-1 ret=0 a=0 u/d=down
Wed Apr 25 15:03:26 2018 Route: Waiting for TUN/TAP interface to come up...
Wed Apr 25 15:03:27 2018 TEST ROUTES: 0/0 succeeded len=-1 ret=0 a=0 u/d=down
Wed Apr 25 15:03:27 2018 Route: Waiting for TUN/TAP interface to come up...
Wed Apr 25 15:03:28 2018 TEST ROUTES: 0/0 succeeded len=-1 ret=0 a=0 u/d=down
Wed Apr 25 15:03:28 2018 Route: Waiting for TUN/TAP interface to come up...
Wed Apr 25 15:03:29 2018 TEST ROUTES: 0/0 succeeded len=-1 ret=0 a=0 u/d=down
Wed Apr 25 15:03:29 2018 Route: Waiting for TUN/TAP interface to come up...
Wed Apr 25 15:03:30 2018 TEST ROUTES: 0/0 succeeded len=-1 ret=0 a=0 u/d=down
Wed Apr 25 15:03:30 2018 Route: Waiting for TUN/TAP interface to come up...
Wed Apr 25 15:03:31 2018 TEST ROUTES: 0/0 succeeded len=-1 ret=0 a=0 u/d=down
Wed Apr 25 15:03:31 2018 Route: Waiting for TUN/TAP interface to come up...
Wed Apr 25 15:03:32 2018 TEST ROUTES: 0/0 succeeded len=-1 ret=0 a=0 u/d=down
Wed Apr 25 15:03:32 2018 Route: Waiting for TUN/TAP interface to come up...
Wed Apr 25 15:03:33 2018 TEST ROUTES: 0/0 succeeded len=-1 ret=0 a=0 u/d=down
Wed Apr 25 15:03:33 2018 Route: Waiting for TUN/TAP interface to come up...
Wed Apr 25 15:03:34 2018 TEST ROUTES: 0/0 succeeded len=-1 ret=0 a=0 u/d=down
Wed Apr 25 15:03:34 2018 Route: Waiting for TUN/TAP interface to come up...
Wed Apr 25 15:03:35 2018 TEST ROUTES: 0/0 succeeded len=-1 ret=0 a=0 u/d=down
Wed Apr 25 15:03:35 2018 Route: Waiting for TUN/TAP interface to come up...
Wed Apr 25 15:03:36 2018 TEST ROUTES: 0/0 succeeded len=-1 ret=0 a=0 u/d=down
Wed Apr 25 15:03:36 2018 Route: Waiting for TUN/TAP interface to come up...
Wed Apr 25 15:03:37 2018 TEST ROUTES: 0/0 succeeded len=-1 ret=0 a=0 u/d=down
Wed Apr 25 15:03:37 2018 Route: Waiting for TUN/TAP interface to come up...
Wed Apr 25 15:03:39 2018 TEST ROUTES: 0/0 succeeded len=-1 ret=0 a=0 u/d=down
Wed Apr 25 15:03:39 2018 Route: Waiting for TUN/TAP interface to come up...
Wed Apr 25 15:03:40 2018 TEST ROUTES: 0/0 succeeded len=-1 ret=0 a=0 u/d=down
Wed Apr 25 15:03:40 2018 Route: Waiting for TUN/TAP interface to come up...
Wed Apr 25 15:03:41 2018 TEST ROUTES: 0/0 succeeded len=-1 ret=0 a=0 u/d=down
Wed Apr 25 15:03:41 2018 Route: Waiting for TUN/TAP interface to come up...
Wed Apr 25 15:03:42 2018 TEST ROUTES: 0/0 succeeded len=-1 ret=0 a=0 u/d=down
Wed Apr 25 15:03:42 2018 Route: Waiting for TUN/TAP interface to come up...
Wed Apr 25 15:03:43 2018 TEST ROUTES: 0/0 succeeded len=-1 ret=0 a=0 u/d=down
Wed Apr 25 15:03:43 2018 Route: Waiting for TUN/TAP interface to come up...
Wed Apr 25 15:03:44 2018 TEST ROUTES: 0/0 succeeded len=-1 ret=0 a=0 u/d=down
Wed Apr 25 15:03:44 2018 Route: Waiting for TUN/TAP interface to come up...
Wed Apr 25 15:03:45 2018 TEST ROUTES: 0/0 succeeded len=-1 ret=0 a=0 u/d=down
Wed Apr 25 15:03:45 2018 Route: Waiting for TUN/TAP interface to come up...
Wed Apr 25 15:03:46 2018 TEST ROUTES: 0/0 succeeded len=-1 ret=0 a=0 u/d=down
Wed Apr 25 15:03:46 2018 Route: Waiting for TUN/TAP interface to come up...
Wed Apr 25 15:03:47 2018 TEST ROUTES: 0/0 succeeded len=-1 ret=0 a=0 u/d=down
Wed Apr 25 15:03:47 2018 C:\Windows\system32\route.exe ADD 10.8.0.1 MASK 255.255.255.255 10.8.0.49
Wed Apr 25 15:03:47 2018 ROUTE: CreateIpForwardEntry succeeded with dwForwardMetric1=20 and dwForwardType=4
Wed Apr 25 15:03:47 2018 Route addition via IPAPI succeeded [adaptive]
SYSTEM ROUTING TABLE
0.0.0.0 0.0.0.0 192.168.8.254 p=0 i=11 t=4 pr=3 a=4573 h=0 m=20/0/0/0/0
10.8.0.1 255.255.255.255 10.8.0.49 p=0 i=20 t=4 pr=3 a=0 h=0 m=20/0/0/0/0
10.8.0.48 255.255.255.252 10.8.0.50 p=0 i=20 t=3 pr=3 a=100164 h=0 m=276/0/0/0/0
10.8.0.50 255.255.255.255 10.8.0.50 p=0 i=20 t=3 pr=3 a=100164 h=0 m=276/0/0/0/0
10.8.0.51 255.255.255.255 10.8.0.50 p=0 i=20 t=3 pr=3 a=100164 h=0 m=276/0/0/0/0
127.0.0.0 255.0.0.0 127.0.0.1 p=0 i=1 t=3 pr=3 a=102373 h=0 m=306/0/0/0/0
127.0.0.1 255.255.255.255 127.0.0.1 p=0 i=1 t=3 pr=3 a=102373 h=0 m=306/0/0/0/0
127.255.255.255 255.255.255.255 127.0.0.1 p=0 i=1 t=3 pr=3 a=102373 h=0 m=306/0/0/0/0
169.254.0.0 255.255.0.0 169.254.106.65 p=0 i=31 t=3 pr=3 a=102334 h=0 m=286/0/0/0/0
169.254.106.65 255.255.255.255 169.254.106.65 p=0 i=31 t=3 pr=3 a=102334 h=0 m=286/0/0/0/0
169.254.255.255 255.255.255.255 169.254.106.65 p=0 i=31 t=3 pr=3 a=102334 h=0 m=286/0/0/0/0
192.168.8.0 255.255.255.0 192.168.8.120 p=0 i=11 t=3 pr=3 a=4573 h=0 m=276/0/0/0/0
192.168.8.120 255.255.255.255 192.168.8.120 p=0 i=11 t=3 pr=3 a=4573 h=0 m=276/0/0/0/0
192.168.8.255 255.255.255.255 192.168.8.120 p=0 i=11 t=3 pr=3 a=4573 h=0 m=276/0/0/0/0
192.168.56.0 255.255.255.0 192.168.56.1 p=0 i=16 t=3 pr=3 a=102342 h=0 m=266/0/0/0/0
192.168.56.1 255.255.255.255 192.168.56.1 p=0 i=16 t=3 pr=3 a=102342 h=0 m=266/0/0/0/0
192.168.56.255 255.255.255.255 192.168.56.1 p=0 i=16 t=3 pr=3 a=102342 h=0 m=266/0/0/0/0
224.0.0.0 240.0.0.0 127.0.0.1 p=0 i=1 t=3 pr=3 a=102373 h=0 m=306/0/0/0/0
224.0.0.0 240.0.0.0 192.168.56.1 p=0 i=16 t=3 pr=3 a=102346 h=0 m=266/0/0/0/0
224.0.0.0 240.0.0.0 192.168.8.120 p=0 i=11 t=3 pr=3 a=102345 h=0 m=276/0/0/0/0
224.0.0.0 240.0.0.0 0.0.0.0 p=0 i=21 t=3 pr=3 a=102345 h=0 m=276/0/0/0/0
224.0.0.0 240.0.0.0 10.8.0.50 p=0 i=20 t=3 pr=3 a=102345 h=0 m=276/0/0/0/0
224.0.0.0 240.0.0.0 169.254.106.65 p=0 i=31 t=3 pr=3 a=102344 h=0 m=286/0/0/0/0
255.255.255.255 255.255.255.255 127.0.0.1 p=0 i=1 t=3 pr=3 a=102373 h=0 m=306/0/0/0/0
255.255.255.255 255.255.255.255 192.168.56.1 p=0 i=16 t=3 pr=3 a=102346 h=0 m=266/0/0/0/0
255.255.255.255 255.255.255.255 192.168.8.120 p=0 i=11 t=3 pr=3 a=102345 h=0 m=276/0/0/0/0
255.255.255.255 255.255.255.255 0.0.0.0 p=0 i=21 t=3 pr=3 a=102345 h=0 m=276/0/0/0/0
255.255.255.255 255.255.255.255 10.8.0.50 p=0 i=20 t=3 pr=3 a=102345 h=0 m=276/0/0/0/0
255.255.255.255 255.255.255.255 169.254.106.65 p=0 i=31 t=3 pr=3 a=102344 h=0 m=286/0/0/0/0
SYSTEM ADAPTER LIST
Npcap Loopback Adapter
  Index = 31
  GUID = {0EBB9881-B861-4BD4-9098-2172D93A6E39}
  IP = 169.254.106.65/255.255.0.0
  MAC = 02:00:4c:4f:4f:50
  GATEWAY = 0.0.0.0/255.255.255.255
  DHCP SERV = 0.0.0.0/255.255.255.255
  DHCP LEASE OBTAINED = Wed Apr 25 15:03:47 2018
  DHCP LEASE EXPIRES  = Wed Apr 25 15:03:47 2018
  DNS SERV =
TAP-Windows Adapter V9 #5
  Index = 24
  GUID = {FF3BFE0C-1DFB-416F-844C-95B4D5A57B61}
  IP = 0.0.0.0/0.0.0.0
  MAC = 00:ff:ff:3b:fe:0c
  GATEWAY = 0.0.0.0/255.255.255.255
  DHCP SERV =
  DHCP LEASE OBTAINED = Wed Apr 25 15:03:47 2018
  DHCP LEASE EXPIRES  = Wed Apr 25 15:03:47 2018
  DNS SERV =
TAP-Windows Adapter V9 #4
  Index = 23
  GUID = {93EC6681-70B4-4D9E-95C5-BA4C45C896FE}
  IP = 0.0.0.0/0.0.0.0
  MAC = 00:ff:93:ec:66:81
  GATEWAY = 0.0.0.0/255.255.255.255
  DHCP SERV =
  DHCP LEASE OBTAINED = Wed Apr 25 15:03:47 2018
  DHCP LEASE EXPIRES  = Wed Apr 25 15:03:47 2018
  DNS SERV =
TAP-Windows Adapter V9 #3
  Index = 22
  GUID = {BB1935BF-67D0-4F3C-B442-A4DEB0F67BFD}
  IP = 0.0.0.0/0.0.0.0
  MAC = 00:ff:bb:19:35:bf
  GATEWAY = 0.0.0.0/255.255.255.255
  DHCP SERV =
  DHCP LEASE OBTAINED = Wed Apr 25 15:03:47 2018
  DHCP LEASE EXPIRES  = Wed Apr 25 15:03:47 2018
  DNS SERV =
TAP-Windows Adapter V9 #2
  Index = 21
  GUID = {2EFEFEDF-8493-411F-A6B9-BE0FA1CDD5C1}
  IP = 0.0.0.0/0.0.0.0
  MAC = 00:ff:2e:fe:fe:df
  GATEWAY = 0.0.0.0/255.255.255.255
  DHCP SERV = 0.0.0.0/255.255.255.255
  DHCP LEASE OBTAINED = Wed Apr 25 15:03:47 2018
  DHCP LEASE EXPIRES  = Wed Apr 25 15:03:47 2018
  DNS SERV =
TAP-Windows Adapter V9
  Index = 20
  GUID = {13C2EDD1-2B6D-4CDF-B435-143C47E95362}
  IP = 10.8.0.50/255.255.255.252
  MAC = 00:ff:13:c2:ed:d1
  GATEWAY = 0.0.0.0/255.255.255.255
  DHCP SERV = 10.8.0.49/255.255.255.255
  DHCP LEASE OBTAINED = Tue Apr 24 11:14:22 2018
  DHCP LEASE EXPIRES  = Wed Apr 24 11:14:22 2019
  DNS SERV =
Microsoft Virtual WiFi Miniport Adapter
  Index = 17
  GUID = {768FF623-5582-468B-B0B9-11C8E769647C}
  IP = 0.0.0.0/0.0.0.0
  MAC = c4:17:fe:ba:8a:f7
  GATEWAY = 0.0.0.0/255.255.255.255
  DHCP SERV =
  DHCP LEASE OBTAINED = Wed Apr 25 15:03:48 2018
  DHCP LEASE EXPIRES  = Wed Apr 25 15:03:48 2018
  DNS SERV =
Dell Wireless 1397 WLAN Mini-Card
  Index = 12
  GUID = {EA5277D1-02A1-41F5-82E3-E3C83B257373}
  IP = 0.0.0.0/0.0.0.0
  MAC = c4:17:fe:ba:8a:f7
  GATEWAY = 192.168.8.254/255.255.255.255
  DHCP SERV =
  DHCP LEASE OBTAINED = Wed Apr 25 15:03:48 2018
  DHCP LEASE EXPIRES  = Wed Apr 25 15:03:48 2018
  DNS SERV =
Realtek PCIe GBE Family Controller
  Index = 11
  GUID = {B8781BB8-1078-4935-B94A-1A21C289C3FA}
  IP = 192.168.8.120/255.255.255.0
  MAC = 00:26:b9:b5:d3:a8
  GATEWAY = 192.168.8.254/255.255.255.255
  DHCP SERV = 192.168.8.254/255.255.255.255
  DHCP LEASE OBTAINED = Wed Apr 25 13:47:33 2018
  DHCP LEASE EXPIRES  = Thu Apr 26 13:47:33 2018
  DNS SERV = 208.67.222.222/255.255.255.255
VirtualBox Host-Only Ethernet Adapter
  Index = 16
  GUID = {AE55BB16-85EF-4F60-84B6-F28651EBB636}
  IP = 192.168.56.1/255.255.255.0
  MAC = 0a:00:27:00:00:10
  GATEWAY = 0.0.0.0/255.255.255.255
  DNS SERV =
Wed Apr 25 15:03:48 2018 Initialization Sequence Completed With Errors ( see http://openvpn.net/faq.html#dhcpclientserv )

Server during this time:

Wed Apr 25 15:03:15 2018 192.168.8.120:64884 TLS: Initial packet from [AF_INET]192.168.8.120:64884, sid=2f35b6f3 3b0e438f
Wed Apr 25 15:03:15 2018 192.168.8.120:64884 VERIFY OK: depth=1, C=UK, ST=Manchester, L=Manchester, O=AAITechnologies, OU=changeme, CN=AAITechnologies, emailAddress=[email address removed]
Wed Apr 25 15:03:15 2018 192.168.8.120:64884 VERIFY OK: depth=0, C=UK, ST=Manchester, L=Manchester, O=AAITechnologies, OU=changeme, CN=craig-test, emailAddress=[email address removed]
Wed Apr 25 15:03:15 2018 192.168.8.120:64884 peer info: IV_VER=2.4.2
Wed Apr 25 15:03:15 2018 192.168.8.120:64884 peer info: IV_PLAT=win
Wed Apr 25 15:03:15 2018 192.168.8.120:64884 peer info: IV_PROTO=2
Wed Apr 25 15:03:15 2018 192.168.8.120:64884 peer info: IV_NCP=2
Wed Apr 25 15:03:15 2018 192.168.8.120:64884 peer info: IV_LZ4=1
Wed Apr 25 15:03:15 2018 192.168.8.120:64884 peer info: IV_LZ4v2=1
Wed Apr 25 15:03:15 2018 192.168.8.120:64884 peer info: IV_LZO=1
Wed Apr 25 15:03:15 2018 192.168.8.120:64884 peer info: IV_COMP_STUB=1
Wed Apr 25 15:03:15 2018 192.168.8.120:64884 peer info: IV_COMP_STUBv2=1
Wed Apr 25 15:03:15 2018 192.168.8.120:64884 peer info: IV_TCPNL=1
Wed Apr 25 15:03:15 2018 192.168.8.120:64884 Control Channel: TLSv1.2, cipher TLSv1/SSLv3 ECDHE-RSA-AES256-GCM-SHA384, 1024 bit RSA
Wed Apr 25 15:03:15 2018 192.168.8.120:64884 [craig-test] Peer Connection Initiated with [AF_INET]192.168.8.120:64884
Wed Apr 25 15:03:15 2018 MULTI: new connection by client 'craig-test' will cause previous active sessions by this client to be dropped.  Remember to use the --duplicate-cn option if you want multiple clients using the same certificate or username to concurrently connect.
Wed Apr 25 15:03:15 2018 MULTI_sva: pool returned IPv4=10.8.0.50, IPv6=(Not enabled)
Wed Apr 25 15:03:15 2018 MULTI: Learn: 10.8.0.50 -> craig-test/192.168.8.120:64884
Wed Apr 25 15:03:15 2018 MULTI: primary virtual IP for craig-test/192.168.8.120:64884: 10.8.0.50
Wed Apr 25 15:03:16 2018 craig-test/192.168.8.120:64884 PUSH: Received control message: 'PUSH_REQUEST'
Wed Apr 25 15:03:16 2018 craig-test/192.168.8.120:64884 SENT CONTROL [craig-test]: 'PUSH_REPLY,explicit-exit-notify 3,route 10.8.0.1,topology net30,ping 10,ping-restart 120,ifconfig 10.8.0.50 10.8.0.49,peer-id 0,cipher AES-256-GCM' (status=1)
Wed Apr 25 15:03:16 2018 craig-test/192.168.8.120:64884 Data Channel: using negotiated cipher 'AES-256-GCM'
Wed Apr 25 15:03:16 2018 craig-test/192.168.8.120:64884 Outgoing Data Channel: Cipher 'AES-256-GCM' initialized with 256 bit key
Wed Apr 25 15:03:16 2018 craig-test/192.168.8.120:64884 Incoming Data Channel: Cipher 'AES-256-GCM' initialized with 256 bit key
Wed Apr 25 15:05:13 2018 192.168.8.120:65020 TLS: Initial packet from [AF_INET]192.168.8.120:65020, sid=8003b4b8 90c1618f
Wed Apr 25 15:05:13 2018 192.168.8.120:65020 VERIFY OK: depth=1, C=UK, ST=Manchester, L=Manchester, O=AAITechnologies, OU=changeme, CN=AAITechnologies, emailAddress=[email address removed]
Wed Apr 25 15:05:13 2018 192.168.8.120:65020 VERIFY OK: depth=0, C=UK, ST=Manchester, L=Manchester, O=AAITechnologies, OU=changeme, CN=craig-test, emailAddress=[email address removed]
Wed Apr 25 15:05:13 2018 192.168.8.120:65020 peer info: IV_VER=2.4.2
Wed Apr 25 15:05:13 2018 192.168.8.120:65020 peer info: IV_PLAT=win
Wed Apr 25 15:05:13 2018 192.168.8.120:65020 peer info: IV_PROTO=2
Wed Apr 25 15:05:13 2018 192.168.8.120:65020 peer info: IV_NCP=2
Wed Apr 25 15:05:13 2018 192.168.8.120:65020 peer info: IV_LZ4=1
Wed Apr 25 15:05:13 2018 192.168.8.120:65020 peer info: IV_LZ4v2=1
Wed Apr 25 15:05:13 2018 192.168.8.120:65020 peer info: IV_LZO=1
Wed Apr 25 15:05:13 2018 192.168.8.120:65020 peer info: IV_COMP_STUB=1
Wed Apr 25 15:05:13 2018 192.168.8.120:65020 peer info: IV_COMP_STUBv2=1
Wed Apr 25 15:05:13 2018 192.168.8.120:65020 peer info: IV_TCPNL=1
Wed Apr 25 15:05:13 2018 192.168.8.120:65020 Control Channel: TLSv1.2, cipher TLSv1/SSLv3 ECDHE-RSA-AES256-GCM-SHA384, 1024 bit RSA
Wed Apr 25 15:05:13 2018 192.168.8.120:65020 [craig-test] Peer Connection Initiated with [AF_INET]192.168.8.120:65020
Wed Apr 25 15:05:13 2018 MULTI: new connection by client 'craig-test' will cause previous active sessions by this client to be dropped.  Remember to use the --duplicate-cn option if you want multiple clients using the same certificate or username to concurrently connect.
Wed Apr 25 15:05:13 2018 MULTI_sva: pool returned IPv4=10.8.0.50, IPv6=(Not enabled)
Wed Apr 25 15:05:13 2018 MULTI: Learn: 10.8.0.50 -> craig-test/192.168.8.120:65020
Wed Apr 25 15:05:13 2018 MULTI: primary virtual IP for craig-test/192.168.8.120:65020: 10.8.0.50
Wed Apr 25 15:05:14 2018 craig-test/192.168.8.120:65020 PUSH: Received control message: 'PUSH_REQUEST'
Wed Apr 25 15:05:14 2018 craig-test/192.168.8.120:65020 SENT CONTROL [craig-test]: 'PUSH_REPLY,explicit-exit-notify 3,route 10.8.0.1,topology net30,ping 10,ping-restart 120,ifconfig 10.8.0.50 10.8.0.49,peer-id 2,cipher AES-256-GCM' (status=1)
Wed Apr 25 15:05:14 2018 craig-test/192.168.8.120:65020 Data Channel: using negotiated cipher 'AES-256-GCM'
Wed Apr 25 15:05:14 2018 craig-test/192.168.8.120:65020 Outgoing Data Channel: Cipher 'AES-256-GCM' initialized with 256 bit key
Wed Apr 25 15:05:14 2018 craig-test/192.168.8.120:65020 Incoming Data Channel: Cipher 'AES-256-GCM' initialized with 256 bit key

Client showing the less common failure mode, where the client stalls sending "PUSH_REQUEST" and never gets an answer- eventually times out and gives up but I killed it before it did. This attempt was around 15s after cancelling a previous attempt so it may be some holdoff period.

Wed Apr 25 14:54:05 2018 OpenVPN 2.4.2 x86_64-w64-mingw32 [SSL (OpenSSL)] [LZO] [LZ4] [PKCS11] [AEAD] built on May 11 2017
Wed Apr 25 14:54:05 2018 Windows version 6.1 (Windows 7) 64bit
Wed Apr 25 14:54:05 2018 library versions: OpenSSL 1.0.2k  26 Jan 2017, LZO 2.10
Wed Apr 25 14:54:05 2018 Outgoing Control Channel Authentication: Using 160 bit message hash 'SHA1' for HMAC authentication
Wed Apr 25 14:54:05 2018 Incoming Control Channel Authentication: Using 160 bit message hash 'SHA1' for HMAC authentication
Wed Apr 25 14:54:05 2018 TCP/UDP: Preserving recently used remote address: [AF_INET]192.168.8.2:1194
Wed Apr 25 14:54:05 2018 Socket Buffers: R=[8192->8192] S=[8192->8192]
Wed Apr 25 14:54:05 2018 UDP link local: (not bound)
Wed Apr 25 14:54:05 2018 UDP link remote: [AF_INET]192.168.8.2:1194
Wed Apr 25 14:54:05 2018 TLS: Initial packet from [AF_INET]192.168.8.2:1194, sid=e999901e a8f418d8
Wed Apr 25 14:54:05 2018 VERIFY OK: depth=1, C=UK, ST=Manchester, L=Manchester, O=AAITechnologies, OU=changeme, CN=AAITechnologies, emailAddress=[email address removed]
Wed Apr 25 14:54:05 2018 VERIFY KU OK
Wed Apr 25 14:54:05 2018 Validating certificate extended key usage
Wed Apr 25 14:54:05 2018 ++ Certificate has EKU (str) TLS Web Server Authentication, expects TLS Web Server Authentication
Wed Apr 25 14:54:05 2018 VERIFY EKU OK
Wed Apr 25 14:54:05 2018 VERIFY OK: depth=0, C=UK, ST=Manchester, L=Manchester, O=AAITechnologies, OU=changeme, CN=AAITechnologies, emailAddress=[email address removed]
Wed Apr 25 14:54:05 2018 Control Channel: TLSv1.2, cipher TLSv1/SSLv3 ECDHE-RSA-AES256-GCM-SHA384, 1024 bit RSA
Wed Apr 25 14:54:05 2018 [AAITechnologies] Peer Connection Initiated with [AF_INET]192.168.8.2:1194
Wed Apr 25 14:54:06 2018 SENT CONTROL [AAITechnologies]: 'PUSH_REQUEST' (status=1)
Wed Apr 25 14:54:11 2018 SENT CONTROL [AAITechnologies]: 'PUSH_REQUEST' (status=1)
Wed Apr 25 14:54:16 2018 SENT CONTROL [AAITechnologies]: 'PUSH_REQUEST' (status=1)
Wed Apr 25 14:54:21 2018 SENT CONTROL [AAITechnologies]: 'PUSH_REQUEST' (status=1)
Wed Apr 25 14:54:26 2018 SENT CONTROL [AAITechnologies]: 'PUSH_REQUEST' (status=1)
Wed Apr 25 14:54:31 2018 SENT CONTROL [AAITechnologies]: 'PUSH_REQUEST' (status=1)
Wed Apr 25 14:54:36 2018 SENT CONTROL [AAITechnologies]: 'PUSH_REQUEST' (status=1)
Wed Apr 25 14:54:41 2018 SENT CONTROL [AAITechnologies]: 'PUSH_REQUEST' (status=1)
Wed Apr 25 14:54:45 2018 SIGTERM[hard,] received, process exiting

Server during this time:

Wed Apr 25 14:54:09 2018 192.168.8.120:65000 TLS: Initial packet from [AF_INET]192.168.8.120:65000, sid=5b41ce0b 0debd2e7
Wed Apr 25 14:54:09 2018 192.168.8.120:65000 VERIFY OK: depth=1, C=UK, ST=Manchester, L=Manchester, O=AAITechnologies, OU=changeme, CN=AAITechnologies, emailAddress=[email address removed]
Wed Apr 25 14:54:09 2018 192.168.8.120:65000 VERIFY OK: depth=0, C=UK, ST=Manchester, L=Manchester, O=AAITechnologies, OU=changeme, CN=craig-test, emailAddress=[email address removed]
Wed Apr 25 14:54:09 2018 192.168.8.120:65000 peer info: IV_VER=2.4.2
Wed Apr 25 14:54:09 2018 192.168.8.120:65000 peer info: IV_PLAT=win
Wed Apr 25 14:54:09 2018 192.168.8.120:65000 peer info: IV_PROTO=2
Wed Apr 25 14:54:09 2018 192.168.8.120:65000 peer info: IV_NCP=2
Wed Apr 25 14:54:09 2018 192.168.8.120:65000 peer info: IV_LZ4=1
Wed Apr 25 14:54:09 2018 192.168.8.120:65000 peer info: IV_LZ4v2=1
Wed Apr 25 14:54:09 2018 192.168.8.120:65000 peer info: IV_LZO=1
Wed Apr 25 14:54:09 2018 192.168.8.120:65000 peer info: IV_COMP_STUB=1
Wed Apr 25 14:54:09 2018 192.168.8.120:65000 peer info: IV_COMP_STUBv2=1
Wed Apr 25 14:54:09 2018 192.168.8.120:65000 peer info: IV_TCPNL=1
Wed Apr 25 14:54:09 2018 192.168.8.120:65000 Control Channel: TLSv1.2, cipher TLSv1/SSLv3 ECDHE-RSA-AES256-GCM-SHA384, 1024 bit RSA
Wed Apr 25 14:54:09 2018 192.168.8.120:65000 [craig-test] Peer Connection Initiated with [AF_INET]192.168.8.120:65000
Wed Apr 25 14:54:09 2018 craig-test/192.168.8.120:65000 MULTI_sva: pool returned IPv4=10.8.0.50, IPv6=(Not enabled)
Wed Apr 25 14:54:09 2018 craig-test/192.168.8.120:65000 MULTI: Learn: 10.8.0.50 -> craig-test/192.168.8.120:65000
Wed Apr 25 14:54:09 2018 craig-test/192.168.8.120:65000 MULTI: primary virtual IP for craig-test/192.168.8.120:65000: 10.8.0.50
Wed Apr 25 14:54:10 2018 Key [AF_INET]192.168.8.120:65000 [0] not initialized (yet), dropping packet.
Wed Apr 25 14:54:10 2018 craig-test/192.168.8.120:52545 Key [AF_INET]192.168.8.120:52545 [0] not initialized (yet), dropping packet.
Wed Apr 25 14:54:12 2018 craig-test/192.168.8.120:52545 Key [AF_INET]192.168.8.120:52545 [0] not initialized (yet), dropping packet.
Wed Apr 25 14:54:12 2018 craig-test/192.168.8.120:52545 Key [AF_INET]192.168.8.120:52545 [0] not initialized (yet), dropping packet.
Wed Apr 25 14:54:22 2018 craig-test/192.168.8.120:52545 Key [AF_INET]192.168.8.120:52545 [0] not initialized (yet), dropping packet.
Wed Apr 25 14:54:32 2018 craig-test/192.168.8.120:52545 Key [AF_INET]192.168.8.120:52545 [0] not initialized (yet), dropping packet.
Wed Apr 25 14:54:42 2018 craig-test/192.168.8.120:52545 Key [AF_INET]192.168.8.120:52545 [0] not initialized (yet), dropping packet.
Wed Apr 25 14:54:52 2018 craig-test/192.168.8.120:52545 Key [AF_INET]192.168.8.120:52545 [0] not initialized (yet), dropping packet.
Wed Apr 25 14:55:02 2018 craig-test/192.168.8.120:52545 Key [AF_INET]192.168.8.120:52545 [0] not initialized (yet), dropping packet.
Wed Apr 25 14:55:12 2018 craig-test/192.168.8.120:52545 Key [AF_INET]192.168.8.120:52545 [0] not initialized (yet), dropping packet.
Wed Apr 25 14:55:24 2018 192.168.8.120:62656 TLS: Initial packet from [AF_INET]192.168.8.120:62656, sid=fb6d08e5 fb1fdbe1
Wed Apr 25 14:55:24 2018 192.168.8.120:62656 VERIFY OK: depth=1, C=UK, ST=Manchester, L=Manchester, O=AAITechnologies, OU=changeme, CN=AAITechnologies, emailAddress=[email address removed]
Wed Apr 25 14:55:24 2018 192.168.8.120:62656 VERIFY OK: depth=0, C=UK, ST=Manchester, L=Manchester, O=AAITechnologies, OU=changeme, CN=craig-test, emailAddress=[email address removed]
Wed Apr 25 14:55:24 2018 192.168.8.120:62656 peer info: IV_VER=2.4.2
Wed Apr 25 14:55:24 2018 192.168.8.120:62656 peer info: IV_PLAT=win
Wed Apr 25 14:55:24 2018 192.168.8.120:62656 peer info: IV_PROTO=2
Wed Apr 25 14:55:24 2018 192.168.8.120:62656 peer info: IV_NCP=2
Wed Apr 25 14:55:24 2018 192.168.8.120:62656 peer info: IV_LZ4=1
Wed Apr 25 14:55:24 2018 192.168.8.120:62656 peer info: IV_LZ4v2=1
Wed Apr 25 14:55:24 2018 192.168.8.120:62656 peer info: IV_LZO=1
Wed Apr 25 14:55:24 2018 192.168.8.120:62656 peer info: IV_COMP_STUB=1
Wed Apr 25 14:55:24 2018 192.168.8.120:62656 peer info: IV_COMP_STUBv2=1
Wed Apr 25 14:55:24 2018 192.168.8.120:62656 peer info: IV_TCPNL=1
Wed Apr 25 14:55:24 2018 192.168.8.120:62656 Control Channel: TLSv1.2, cipher TLSv1/SSLv3 ECDHE-RSA-AES256-GCM-SHA384, 1024 bit RSA
Wed Apr 25 14:55:24 2018 192.168.8.120:62656 [craig-test] Peer Connection Initiated with [AF_INET]192.168.8.120:62656
Wed Apr 25 14:55:24 2018 MULTI: new connection by client 'craig-test' will cause previous active sessions by this client to be dropped.  Remember to use the --duplicate-cn option if you want multiple clients using the same certificate or username to concurrently connect.
Wed Apr 25 14:55:24 2018 MULTI_sva: pool returned IPv4=10.8.0.50, IPv6=(Not enabled)
Wed Apr 25 14:55:24 2018 MULTI: Learn: 10.8.0.50 -> craig-test/192.168.8.120:62656
Wed Apr 25 14:55:24 2018 MULTI: primary virtual IP for craig-test/192.168.8.120:62656: 10.8.0.50
Wed Apr 25 14:55:25 2018 craig-test/192.168.8.120:62656 PUSH: Received control message: 'PUSH_REQUEST'
Wed Apr 25 14:55:25 2018 craig-test/192.168.8.120:62656 SENT CONTROL [craig-test]: 'PUSH_REPLY,explicit-exit-notify 3,route 10.8.0.1,topology net30,ping 10,ping-restart 120,ifconfig 10.8.0.50 10.8.0.49,peer-id 2,cipher AES-256-GCM' (status=1)
Wed Apr 25 14:55:25 2018 craig-test/192.168.8.120:62656 Data Channel: using negotiated cipher 'AES-256-GCM'
Wed Apr 25 14:55:25 2018 craig-test/192.168.8.120:62656 Outgoing Data Channel: Cipher 'AES-256-GCM' initialized with 256 bit key
Wed Apr 25 14:55:25 2018 craig-test/192.168.8.120:62656 Incoming Data Channel: Cipher 'AES-256-GCM' initialized with 256 bit key

For completeness here's the config files.

##############################################
# Sample client-side OpenVPN 2.0 config file #
# for connecting to multi-client server. #
# #
# This configuration can be used by multiple #
# clients, however each client should have #
# its own cert and key files. #
# #
# On Windows, you might want to rename this #
# file so it has a .ovpn extension #
##############################################

# Specify that we are a client and that we
# will be pulling certain config file directives
# from the server.
client

# Use the same setting as you are using on
# the server.
# On most systems, the VPN will not function
# unless you partially or fully disable
# the firewall for the TUN/TAP interface.
;dev tap0
dev tun

# Windows needs the TAP-Win32 adapter name
# from the Network Connections panel
# if you have more than one. On XP SP2,
# you may need to disable the firewall
# for the TAP adapter.
;dev-node MyTap

# Are we connecting to a TCP or
# UDP server? Use the same setting as
# on the server.
;proto tcp
proto udp

# The hostname/IP and port of the server.
# You can have multiple remote entries
# to load balance between the servers.
;remote 192.168.1.129 1194
;remote aai.dynu.net 1194
remote 192.168.8.2 1194

# Choose a random host from the remote
# list for load-balancing. Otherwise
# try hosts in the order specified.
;remote-random

# Keep trying indefinitely to resolve the
# host name of the OpenVPN server. Very useful
# on machines which are not permanently connected
# to the internet such as laptops.
resolv-retry infinite

# Most clients don't need to bind to
# a specific local port number.
nobind

# Downgrade privileges after initialization (non-Windows only)
;user nobody
;group nobody

# Try to preserve some state across restarts.
persist-key
persist-tun

# If you are connecting through an
# HTTP proxy to reach the actual OpenVPN
# server, put the proxy server/IP and
# port number here. See the man page
# if your proxy server requires
# authentication.
;http-proxy-retry # retry on connection failures
;http-proxy [proxy server] [proxy port #]

# Wireless networks often produce a lot
# of duplicate packets. Set this flag
# to silence duplicate packet warnings.
;mute-replay-warnings

# SSL/TLS parms.
# See the server config file for more
# description. It's best to use
# a separate .crt/.key file pair
# for each client. A single ca
# file can be used for all clients.
ca ca.crt
cert craig-test.crt
key craig-test.key

# Verify server certificate by checking that the
# certicate has the correct key usage set.
# This is an important precaution to protect against
# a potential attack discussed here:
# http://openvpn.net/howto.html#mitm
#
# To use this feature, you will need to generate
# your server certificates with the keyUsage set to
# digitalSignature, keyEncipherment
# and the extendedKeyUsage to
# serverAuth
# EasyRSA can do this for you.
remote-cert-tls server

# If a tls-auth key is used on the server
# then every client must also have the key.
tls-auth ta.key 1

# Select a cryptographic cipher.
# If the cipher option is used on the server
# then you must also specify it here.
# Note that 2.4 client/server will automatically
# negotiate AES-256-GCM in TLS mode.
# See also the ncp-cipher option in the manpage
cipher AES-128-CBC

# Enable compression on the VPN link.
# Don't enable this unless it is also
# enabled in the server config file.
comp-lzo

# Set log file verbosity. 3 is the original value
verb 3

# Silence repeating messages
;mute 20

#for testing
#keepalive 2 0
#reneg-sec 0

#################################################
# Sample OpenVPN 2.0 config file for #
# multi-client server. #
# #
# This file is for the server side #
# of a many-clients <-> one-server #
# OpenVPN configuration. #
# #
# OpenVPN also supports #
# single-machine <-> single-machine #
# configurations (See the Examples page #
# on the web site for more info). #
# #
# This config should work on Windows #
# or Linux/BSD systems. Remember on #
# Windows to quote pathnames and use #
# double backslashes, e.g.: #
# "C:\\Program Files\\OpenVPN\\config\\foo.key" #
# #
# Comments are preceded with '#' or ';' #
#################################################

#script-security 3 system

# Which local IP address should OpenVPN
# listen on? (optional)
;local a.b.c.d

# Which TCP/UDP port should OpenVPN listen on?
# If you want to run multiple OpenVPN instances
# on the same machine, use a different port
# number for each one. You will need to
# open up this port on your firewall.
port 1194

# TCP or UDP server?
;proto tcp
proto udp4

# "dev tun" will create a routed IP tunnel,
# "dev tap" will create an ethernet tunnel.
# Use "dev tap0" if you are ethernet bridging
# and have precreated a tap0 virtual interface
# and bridged it with your ethernet interface.
# If you want to control access policies
# over the VPN, you must create firewall
# rules for the the TUN/TAP interface.
# On non-Windows systems, you can give
# an explicit unit number, such as tun0.
# On Windows, use "dev-node" for this.
# On most systems, the VPN will not function
# unless you partially or fully disable
# the firewall for the TUN/TAP interface.
;dev tap0
dev tun

# Windows needs the TAP-Win32 adapter name
# from the Network Connections panel if you
# have more than one. On XP SP2 or higher,
# you may need to selectively disable the
# Windows firewall for the TAP adapter.
# Non-Windows systems usually don't need this.
;dev-node MyTap

# SSL/TLS root certificate (ca), certificate
# (cert), and private key (key). Each client
# and the server must have their own cert and
# key file. The server and all clients will
# use the same ca file.
#
# See the "easy-rsa" directory for a series
# of scripts for generating RSA certificates
# and private keys. Remember to use
# a unique Common Name for the server
# and each of the client certificates.
#
# Any X509 key management system can be used.
# OpenVPN can also use a PKCS #12 formatted key file
# (see "pkcs12" directive in man page).
ca ca.crt
cert server.crt
key server.key # This file should be kept secret

# Diffie hellman parameters.
# Generate your own with:
# openssl dhparam -out dh1024.pem 1024
# Substitute 2048 for 1024 if you are using
# 2048 bit keys.
dh dh1024.pem

# Configure server mode and supply a VPN subnet
# for OpenVPN to draw client addresses from.
# The server will take 10.8.0.1 for itself,
# the rest will be made available to clients.
# Each client will be able to reach the server
# on 10.8.0.1. Comment this line out if you are
# ethernet bridging. See the man page for more info.
server 10.8.0.0 255.255.255.0

# Maintain a record of client <-> virtual IP address
# associations in this file. If OpenVPN goes down or
# is restarted, reconnecting clients can be assigned
# the same virtual IP address from the pool that was
# previously assigned.
ifconfig-pool-persist ipp.txt

# Configure server mode for ethernet bridging.
# You must first use your OS's bridging capability
# to bridge the TAP interface with the ethernet
# NIC interface. Then you must manually set the
# IP/netmask on the bridge interface, here we
# assume 10.8.0.4/255.255.255.0. Finally we
# must set aside an IP range in this subnet
# (start=10.8.0.50 end=10.8.0.100) to allocate
# to connecting clients. Leave this line commented
# out unless you are ethernet bridging.
;server-bridge 10.8.0.1 255.255.255.0 10.8.0.50 10.8.0.100

# Configure server mode for ethernet bridging
# using a DHCP-proxy, where clients talk
# to the OpenVPN server-side DHCP server
# to receive their IP address allocation
# and DNS server addresses. You must first use
# your OS's bridging capability to bridge the TAP
# interface with the ethernet NIC interface.
# Note: this mode only works on clients (such as
# Windows), where the client-side TAP adapter is
# bound to a DHCP client.
;server-bridge

# Push routes to the client to allow it
# to reach other private subnets behind
# the server. Remember that these
# private subnets will also need
# to know to route the OpenVPN client
# address pool (10.8.0.0/255.255.255.0)
# back to the OpenVPN server.
;push "route 192.168.1.1 255.255.255.0"
;push "route 192.168.20.0 255.255.255.0"

# To assign specific IP addresses to specific
# clients or if a connecting client has a private
# subnet behind it that should also have VPN access,
# use the subdirectory "ccd" for client-specific
# configuration files (see man page for more info).

# EXAMPLE: Suppose the client
# having the certificate common name "Thelonious"
# also has a small subnet behind his connecting
# machine, such as 192.168.40.128/255.255.255.248.
# First, uncomment out these lines:
;client-config-dir ccd
;route 192.168.40.128 255.255.255.248
# Then create a file ccd/Thelonious with this line:
# iroute 192.168.40.128 255.255.255.248
# This will allow Thelonious' private subnet to
# access the VPN. This example will only work
# if you are routing, not bridging, i.e. you are
# using "dev tun" and "server" directives.

# EXAMPLE: Suppose you want to give
# Thelonious a fixed VPN IP address of 10.9.0.1.
# First uncomment out these lines:
;client-config-dir ccd
;route 10.9.0.0 255.255.255.252
# Then add this line to ccd/Thelonious:
# ifconfig-push 10.9.0.1 10.9.0.2

# Suppose that you want to enable different
# firewall access policies for different groups
# of clients. There are two methods:
# (1) Run multiple OpenVPN daemons, one for each
# group, and firewall the TUN/TAP interface
# for each group/daemon appropriately.
# (2) (Advanced) Create a script to dynamically
# modify the firewall in response to access
# from different clients. See man
# page for more info on learn-address script.
;learn-address ./script

# If enabled, this directive will configure
# all clients to redirect their default
# network gateway through the VPN, causing
# all IP traffic such as web browsing and
# and DNS lookups to go through the VPN
# (The OpenVPN server machine may need to NAT
# or bridge the TUN/TAP interface to the internet
# in order for this to work properly).
;push "redirect-gateway def1 bypass-dhcp"

# Certain Windows-specific network settings
# can be pushed to clients, such as DNS
# or WINS server addresses. CAVEAT:
# http://openvpn.net/faq.html#dhcpcaveats
# The addresses below refer to the public
# DNS servers provided by opendns.com.
;push "dhcp-option DNS 208.67.222.222"
;push "dhcp-option DNS 208.67.220.220"

# Uncomment this directive to allow different
# clients to be able to "see" each other.
# By default, clients will only see the server.
# To force clients to only see the server, you
# will also need to appropriately firewall the
# server's TUN/TAP interface.
;client-to-client

# Uncomment this directive if multiple clients
# might connect with the same certificate/key
# files or common names. This is recommended
# only for testing purposes. For production use,
# each client should have its own certificate/key
# pair.
#
# IF YOU HAVE NOT GENERATED INDIVIDUAL
# CERTIFICATE/KEY PAIRS FOR EACH CLIENT,
# EACH HAVING ITS OWN UNIQUE "COMMON NAME",
# UNCOMMENT THIS LINE OUT.
;duplicate-cn

# The keepalive directive causes ping-like
# messages to be sent back and forth over
# the link so that each side knows when
# the other side has gone down.
# Ping every 10 seconds, assume that remote
# peer is down if no ping received during
# a 120 second time period.
keepalive 10 120

# For extra security beyond that provided
# by SSL/TLS, create an "HMAC firewall"
# to help block DoS attacks and UDP port flooding.
#
# Generate with:
# openvpn --genkey --secret ta.key
#
# The server and each client must have
# a copy of this key.
# The second parameter should be '0'
# on the server and '1' on the clients.
tls-auth ta.key 0 # This file is secret

# Select a cryptographic cipher.
# This config item must be copied to
# the client config file as well.
;cipher BF-CBC # Blowfish (default)
cipher AES-128-CBC # AES
;cipher DES-EDE3-CBC # Triple-DES

# Enable compression on the VPN link.
# If you enable it here, you must also
# enable it in the client config file.
comp-lzo

# The maximum number of concurrently connected
# clients we want to allow.
;max-clients 100

# It's a good idea to reduce the OpenVPN
# daemon's privileges after initialization.
#
# You can uncomment this out on
# non-Windows systems.
user nobody
group nogroup

# The persist options will try to avoid
# accessing certain resources on restart
# that may no longer be accessible because
# of the privilege downgrade.
persist-key
persist-tun

# Output a short status file showing
# current connections, truncated
# and rewritten every minute.
status openvpn-status.log

# By default, log messages will go to the syslog (or
# on Windows, if running as a service, they will go to
# the "\Program Files\OpenVPN\log" directory).
# Use log or log-append to override this default.
# "log" will truncate the log file on OpenVPN startup,
# while "log-append" will append to it. Use one
# or the other (but not both).
;log openvpn.log
;log-append openvpn.log

# Set the appropriate level of log
# file verbosity.
#
# 0 is silent, except for fatal errors
# 4 is reasonable for general usage
# 5 and 6 can help to debug connection problems
# 9 is extremely verbose
verb 3

# Silence repeating messages. At most 20
# sequential messages of the same message
# category will be output to the log.
;mute 20

#up "/etc/openvpn/up.sh"
#down "/etc/openvpn/down.sh"
push "explicit-exit-notify 3"

TinCanTech

Try adding --duplicate-cn to your server config.

craiggraham

Thanks, I'll have a go next time I'm in the office. Weirdly, the past two days I've been at home and it's been working fine. I've changed nothing aside from the address I'm VPNing to- it's now the external address of the office because of the different physical location. Yet when I did get it working last week, I was physically in the office. Don't understand it so I'll first see if it continues to work next time I'm in the office having not made any other changes.

In terms of keys, the server and each user have their own .key, .crt and .csr files and the CN field is different in each case. Well, the server has no .csr file. This has been the case for months- everything was working fine when pointing at the Linux box in a different physical location.