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FAQ
247-i-am-having-problems-running-openvpn-with-the-windows-xp-firewall-enabled-whats-wrong
249-upgraded-the-openvpn-daemon-on-one-side-of-the-connection-to-v20-and-now-it-cant-connect
251-openvpn-server-successfully-connected-a-client-to-it-but-when-i-try-to-connect-a-second-client-the
253-tls-error-tls-key-negotiation-failed-to-occur-within-60-seconds-check-your-network-connectivity
255-qconnection-initiated-with-xxxxq-but-i-cannot-ping-the-server-through-the-vpn
257-can-an-openvpn-server-be-set-up-on-a-machine-with-a-single-nic
259-tap-win32-adapter-is-not-coming-up-initialization-sequence-completed-with-errors
261-when-i-try-configure-on-red-hat-9-linux-or-higher-it-complains-about-openssl-headers-not-found
263-openvpn-can-ping-both-peers-but-i-cant-reach-any-of-the-other-machines-on-the-remote-subnet
265-how-do-i-enable-ip-forwarding
267-i-am-having-trouble-getting-openvpn-1x-to-talk-with-openvpn-20
269-tue-oct-26-143448-2004-36880-write-udpv4--no-buffer-space-available-code105
271-i-can-ping-through-the-tunnel-but-any-real-work-causes-it-to-lock-up-is-this-an-mtu-problem
273-qifconfig-poolq-option-use-a-30-subnet-4-private-ip-addresses-per-client-when-used-in-tun-mode
275-why-cant-i-run-openvpn-on-windows-from-a-non-admin-user-account
277-i-uninstalled-openvpn-on-windows-2000-and-now-it-appears-that-winsock-is-broken-how-to-fix
279-are-there-any-issues-related-to-pushing-dhcp-options-to-windows-clients
281-what-to-do-if-the-installation-of-the-tap-win32-driver-fails
283-can-i-run-multiple-openvpn-tunnels-on-a-single-machine
285-everything-seems-to-be-configured-correctly-but-i-cant-ping-across-the-tunnel
287-is-ipv6-support-plannedin-the-works
289-how-can-i-build-a-binary-rpm-package-for-my-specific-linux-platform
291-on-slackware-i-get-the-error-cipher-algorithm-bf-cbc-not-found-openssl
293-what-is-the-principle-behind-openvpn-tunnels
295-are-there-any-known-security-vulnerabilities-with-openvpn
297-is-it-important-to-openvpn-security-practices-to-build-an-intermediate-certificate-authoritykey
299-can-openvpn-handle-the-situation-where-both-ends-of-the-connection-are-dynamic
301-does-openvpn-support-certificate-revocation-lists-crls
303-how-stable-is-the-openvpn-protocol-ie-can-old-versions-of-openvpn-talk-to-new-versions
305-what-is-the-difference-between-a-tun-device-and-a-tap-device
307-what-is-bridging
309-what-is-the-difference-between-bridging-and-routing
311-what-are-the-fundamental-differences-between-bridging-and-routing-in-terms-of-configuration
313-how-can-i-connect-windows-xp-to-a-linux-based-samba-server-using-routing-rather-than-bridging
315-i-get-the-error-cannot-ioctl-tunsetiff-tun0-file-descriptor-in-bad-state-errno77
317-qmulti-bad-source-address-from-client--packet-droppedq-or-qget-inst-by-virt-failedq
319-how-do-i-make-the-windows-network-adapter-my-default-adapter-again
321-remap-local-addresses-to-connect-two-networks-with-an-overlap-in-the-private-address-range
323-i-want-to-set-up-an-ethernet-bridge-on-the-1921681024-subnet-existing-dhcp
325-openvpn-as-a--forking-tcp-server-which-can-service-multiple-clients-over-a-single-tcp-port
327-changed-hex-bytes-in-the-static-key-the-key-still-connects-to-a-remote-peer-using-the-original-key
328-route-and-route-ipv6-in-ccd-files
329-problems-with-tls
330-CanIUseAWebBrowserAsAnOpenvpnClient
331-DoesOpenvpnSupportIpsecOrPptp
332-CanOpenvpnTunnelOverATcpConnection
333-WhyChooseTLSAsOpenvpnsUnderlyingAuthenticationAndKeyNegotiationProtocol
334-WhyMyOpenVPNTunnelDoesNot
GSoC2026_ideas
GSoC_howtopropose
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Topology
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easy_rsa_fr
easyrsa-upgrade
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ReleaseHistory
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CVE-2016-10229
CVE-2017-12166
CVE-2018-7544
CVE-2020-15078
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CVE-2021-3606
CVE-2022-0547
CVE-2023-46849
CVE-2023-46850
CVE-2023-6247
CVE-2023-7235
CVE-2024-1305
CVE-2024-13454
CVE-2024-24974
CVE-2024-27459
CVE-2024-27903
CVE-2024-28882
CVE-2024-4877
CVE-2024-5198
CVE-2024-5594
CVE-2025-10680
CVE-2025-12106
CVE-2025-13086
CVE-2025-13751
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CVE-2026-13379
CVE-2026-13698
CVE-2026-2738
CVE-2026-35058
CVE-2026-40215
CVE-2026-63649
CVE-2026-63650
CVE-2026-78043
CVE-2026-78221
CVE-2026-81738
CVE-2026-81830
CVE-2026-82312
CVE-2026-82325
CVE-2026-84226
CVE-2026-84256
CVE-2026-84471
CVE-2026-84732
DUHKattack
NSISBug1125
QuarkslabAndCryptographyEngineerAudits
SWEET32
SecurityAnnouncement-97597e732b
SecurityAnnouncement-FREAK
SecurityAnnouncement-f375aa67cc
SecurityOverview
SecurityVulnerabilities
TLSTripleHandshakeVulnerabilityAndOpenVPN
TapWindows6BufferOverflowVulnerability
TunnelCrack
UnquotedServicePathIn24WindowsInstallers
VORACLE
VulnerabilitiesFixedInOpenSSL1_0_1i
VulnerabilitiesFixedInOpenSSL1_0_1j
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VulnerabilitiesFixedInOpenVPN243
heartbleed
An Otter Wiki
Archived
Page Index
Toggle page headings
A
ACKSystemReview
Current ACK/NACK code review system
Scope
Evolution
Pros
Limitations
Cons
Raw data
Generic statistics
ACKs by person
Effects of the ACK system on patches
Big patchsets
Conclusions
B
BuildingTapWindows
Setting up the Windows build computer
Building TAP-windows
BuildingUsingGenericBuildsystem
Building natively on *NIX
Cross-compiling on *NIX ("generic" subdir)
Creating a NSIS installer ("windows-nsis" subdir)
Code-signing
Making the release builds of OpenVPN
External links
D
DynamicDNS
Requirements
Installation
Configuration
Installing DDNS TSIG Keys
Sharing a Zone with DHCP
ISC DHCPD Server Integration
To Do
IPv6
DUID and dhcp-client-identifier
More Documentation and Testing
G
GettingOpenvpnBuild
Fetching openvpn-build using Git
Getting openvpn-build releases
H
HLKTesting
Getting source code for tap-windows6
HLK test environment overview
Installing HLK software
Preparing HLK clients
Setting up OpenVPN for HLK tests
Preparing HLK studio/controller
Select the device to test
Set product type
Loading compatibility playlists
Adding machines to pool
Configuring and running the mandatory HLK tests
Multi-machine tests
NDISTest 6.5 - 2 machine - Linkcheck
NDISTest 6.0 - 2 Machine - 2c_Priority
NDISTest 6.5 - 2 Machine - AddressChange
NDISTest 6.5 - 2 Machine - E2EPerf
NDISTest 6.0 - 1 machine - 1c_FaultHandling
NDISTest 6.0 - 1 machine - 1c_NdisRequestCov
NDISTest 6.0 - 1 machine - 1c_Registry
NDISTest 6.0 - 2 machine - 2c_Mini6Stress
TDI filters and LSPs are not allowed
Static Tools Logo Test
Various known issues
Failures to Copy downlevel NDISTest binaries
HLK clients can't be activated
Packet transmission too slow
Packets reordering
Address Change test failures
HLK client version mismatches
Controller misuses support machine
Driver parameters
Test-signing issues
HLK logging
Debugging
Addendum
Default browser on HLK controller
Tap-windows6 as virtual network device
Note on reboots
Firewall rules for HLK server and clients
External links
I
IOSinline
N
Nonprivileged
Solution for Windows XP
New and working solution for Windows 7 (and above)
2 scripts that help us
Script 1 create_main_task_only_runonce.cmd
Script 2 create_usertask.cmd
Install OpenVPN-GUI
Prepare and fix Registry Keys
Copy script files to target
Setup the main task
Change OpenVPN-GUI shortcut
Test it!
First logon
Main scheduled task will execute
Security related information
Future logons
Main scheduled task will execute
User task will execute
Summary
O
OpenvpnMSIInstaller
Installer targets
Notes
Optimizing Performance on Gigabit Networks
Network Setup
Understanding the Flow of Packets
Standard Setup
Tweaked Setup
Explanation
txqueuelen
Using OpenSSL 1.0.0 with AES-NI patch
Explanation
Using OpenSSL 1.0.0 with AES-NI capable hardware
For reference: using no encryption
10 Gigabit networks
P
PerformanceTesting
Goals
Prequisites
Test cases
Throughput tests
Connection tests
Test results
Test setup details for m1.small servers
Test setup details for m1.large servers
MP-2 results
OpenVPN 2.2.1/m1.large/UDP/IPv4/OpenSSL/20 clients (MP-2)
MP-3 results
OpenVPN 2.2.1/m1.large/UDP/IPv4/OpenSSL/50 clients (MP-3) ===
MP-4 results
Test environments
General considerations
Amazon EC2
Local (LAN)
Configuring test server(s)
Configuring test clients
Tools
Deploying clients
Generating network traffic
Collecting data
Notes
Head/tail effect
PrivilegeSeparation
OpenVPN use-cases
Standalone workstations
Enterprise workstations
Practical privilege separation models (enterprise use-case)
GUI/service ==
alonbl notes
Interactive service
COM+
Alonbl notes
External links
R
RoadMap
Introduction
Similar projects
Current issues and potential fixes
Monolithic architecture
Threading
Event system
OpenVPN 3.0: Development issues
Organic vs. planned development
Start from scratch vs. incremental approach
Generic network stack vs. focus on VPN functionality
OpenVPN 3.0: Design and implementation
S
SecurityOverview
OpenVPN Protocol
StaticKeyMiniHowto
Static Key advantages
Static Key disadvantages
Simple Example
Server configuration file
Client configuration file
Firewall configuration
Testing the VPN
Expanding on the Simple Example
Use compression on the VPN link
Make the link more resistent to connection failures
Run OpenVPN as a daemon (Linux/BSD/Solaris/MacOSX only) ==
Allow client to reach entire server subnet
T
TapWindowsLicenseChange
TracWikiReplacements
Requirements
General observations
Open source wikis that seem most suitable
Seemingly good candidates that got rejected after a closer look
Other possibly suitable open source wikis
Unsuitable alternatives that were reviewed
Open source wikis with wrong focus
Non-open source wikis
Open source wikis that are outdated
U
UsingSmartcards
External resources
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