What are the differences between using dev tap and dev tun for openvpn? I know the different modes cannot inter-operate. What is the technical differences, other then just layer 2 vs 3 operation. Are there different performance characteristics, or different levels of overhead. Which mode is better. What functionality is exclusively available in each mode.

  • Please explain the difference? whats ethernet bridging and why is it bad? Commented Jun 7, 2009 at 16:13

11 Answers 11


if it's ok to create vpn on layer 3 (one more hop between subnets) - go for tun.

if you need to bridge two ethernet segments in two different locations - then use tap. in such setup you can have computers in the same ip subnet (eg on both ends of vpn, and they'll be able to 'talk' to each other directly without any changes in their routing tables. vpn will act like ethernet switch. this might sound cool and is useful in some cases but i would advice not to go for it unless you really need it. if you choose such layer 2 bridging setup - there will be a bit of 'garbage' (that is broadcast packets) going across your vpn.

using tap you'll have slightly more overhead - besides ip headers also 38B or more of ethernet headers are going to be sent via the tunnel (depending on the type of your traffic - it'll possibly introduce more fragmentation).

  • If I run traceroute from computer in one location to computer in another location, I can see that gateway is added in the communication when using VPN TUN. So is it confirmed that TAP communication is straight? So in traceroute output I will see just first item?
    – laimison
    Commented Nov 11, 2020 at 14:59
  • No, it isn't "straight". Traceroute is simply not the right tool to consider a performance the network. It obviously won't count Ethernet switches along the way, and in case of any VPN it doesn't count, say, hops the encapsulated packet encountered. OpenVPN in tap mode looks like a switch, that's granted, but it doesn't remove any real hops the traffic went. If you need a useful metric, use RTT (round trip time) statistics, which could be obtained with simple ping. Commented Nov 9, 2021 at 6:22
  • You could configure a VLAN to dismiss the "garbage" broadcast traffic from one subnet Commented Jul 21, 2022 at 9:03
  • Let's say I have two subnetworks and What exactly happens when I configure OpenVPN in tap mode? Should I make them use the same subnet and their IPs unique first? What if I want to use DHCP? How does OpenVPN in tap mode works exactly? AFAICT in tun mode you have 1 tun interface on each side (1 tunnel). These 2 interfaces form a subnet consisting of 2 nodes. Each node is a gateway. In tap mode you supposedly have a tap interface bridged to a physical NIC on each side. And probably also one tunnel. And the tunnel is probably also like a bridge (L2)...
    – x-yuri
    Commented Apr 16 at 22:48
  • tap works like an ethernet switch / bridge; if you have two separate DHCP servers - one on, another on and then you bridge them via tap - you'll create a race condition and risk that users from one of the subnets will get DHCP responses from other subnet. in short - sounds like tap is not the right solution.
    – pQd
    Commented Apr 20 at 6:59

I chose "tap" when setting up a VPN for a friend who owned a small business because his office uses a tangle of Windows machines, commercial printers, and a Samba file server. Some of them use pure TCP/IP, some seem to only use NetBIOS (and thus need Ethernet broadcast packets) to communicate, and some I'm not even sure of.

If I had chosen "tun", I would probably have faced lots of broken services — lots of things that worked while you are in the office physically, but then would break when you went off-site and your laptop couldn't "see" the devices on the Ethernet subnet anymore.

But by choosing "tap", I tell the VPN to make remote machines feel exactly like they're on the LAN, with broadcast Ethernet packets and raw Ethernet protocols available for communicating with printers and file servers and for powering their Network Neighborhood display. It works great, and I never get reports of things that don't work offsite!

  • What happens when VPN server dies in VPN TAP mode in 3 locations setup? I'm brainstorming if there is no downside for TAP, because in TUN mode you can connect each location to each location. There are just different subnets connected to each server. So if one VPN server dies, other two locations will be able to communicate. To me it sounds like not achievable in TAP or at least it needs something additional, any thoughts?
    – laimison
    Commented Nov 11, 2020 at 17:23

I always set up tun. Tap is used by ethernet bridging in OpenVPN and introduces an unprecendented level of complexity that is simply not worth bothering with. Usually when a VPN needs to be installed, its needed now, and complex deployments don't come fast.

The OpenVPN FAQ and the Ethernet Bridging HOWTO are excellent resources on this topic.

  • 14
    In my experience, tun is easier to setup but doesn't handle as many network configurations, so you run into a lot more weird networking problems. In contrast, tap is a bit more complicated to setup, but once you do, it typically "just works" for everyone.
    – Cerin
    Commented Mar 28, 2013 at 21:36

Because I find simple advice hard to come by:

You can use TUN if you just use the VPN to connect to the internet.

You need to use TAP if you want to connect to the actual remote network (printers, remote desktops, etc.)

  • 4
    You can still connect to remote desktops (RDP/VNC/etc) with tun. Commented Jan 5, 2021 at 15:09
  • 1
    @KongChunHo: I'm pretty sure I've had trouble with some stuff (printing?) with tun... have you not?
    – user541686
    Commented Jun 24, 2021 at 22:06

If you plan to connect mobile ( iOS or Android ) devices using OpenVPN, then you should use TUN as currently TAP is not supported by OpenVPN on them:

TAP drawbacks: ..... can not be used with Android or iOS devices

  • 2
    TAP is supported on Android through a third party app: OpenVPN Client (Developer: colucci-web.it)
    – Boo
    Commented Feb 6, 2017 at 14:43

I started out using tun, but switched to tap since I didn't like the use of a /30 subnet for each PC (I need to support Windows). I found that to be wasteful and confusing.

Then I discovered the "topology subnet" option on the server. Works with the 2.1 RCs (not 2.0), but it gives me all the advantages of tun (no bridging, performance, routing, etc) with the convenience of one (sequential) IP address per (windows) machine.

  • For VPN you'll use some RFC1918 private subnet, and if you say use, which has 2²⁴=16777216 addresses and 4194304 /30 subnets. The argument in the answer is valid only if this is not enough for you, but I strongly doubt that. Also, the answer went out of the truth. The recent OpenVPN versions could work on Windows in "tun" mode even without these /30 subnets. net30 topology is deprecated long ago. Commented Nov 9, 2021 at 6:29

My "rules of thumb"
TUN - if you ONLY need access to resources connected directly to the OpenVPN server machine at the other end, and there are no Windows issues. A little creativity here can help, by making resources "appear" to be local to the OpenVPN server. (examples might be a CUPS connection to a network printer, or a Samba share on another machine MOUNTed on the OpenVPN server.)

TAP - if you need access to multiple resources (machines, storage, printers, devices) connected via the network at the other end. TAP may also be required for certain Windows applications.

TUN normally confines VPN access to a single machine (IP address) and therefore (presumably) better security through limited connectivity to the far-side network. TUN connection will create less load on the VPN tunnel, and in turn the far-side network because only traffic to/from the single IP address will cross the VPN to the other side. IP Routes to other stations in the subnet are not included, so traffic is not sent across the VPN tunnel and little or no communication is possible beyond the OpenVPN server.

TAP - usually allows packets to flow freely between the endpoints. This gives the flexibility of communication with other stations on the far-side network, including some methods used by older Microsoft software. TAP has the inherent security exposures involved with granting outside access "behind the firewall". It will allow more traffic packets to flow through the VPN tunnel. This also opens the possibility of address conflicts between the endpoints.

There are differences in latency because of the stack layer, but in most end-user scenarios the connection speed of the endpoints is probably a more significant contributor to latency than the particular stack layer of the transmission. If latency is at issue, it might be a good idea to consider other alternatives. Current GHz-level multiprocessors normally outrun the bottleneck of transmission via the internet.

"Better" and "Worse" are not definable without a context.
(This is the consultant's favorite answer, "Well that depends...")
Is a Ferrari "better" than a dump truck? If you are trying to go fast, it may be; but if you're trying to haul heavy loads, probably not.

Constraints like "need for access" and "security requirements" must be defined, as well as defining constraints like network throughput and equipment limitations, before one can decide whether TUN or TAP is better-suited to your needs.

  • 2
    This is absolutely wrong. With proper routing and firewall setup (which is required anyway if you deploy VPN) the access could be made to any resource via either mode. This is not the proper criteria to choose the virtual NIC mode. The correct criteria were described in the wiki. Commented Nov 9, 2021 at 6:17

Setting up TAP requires almost no additional work from the person setting it up.

Of course if you know how to setup TUN but don't understand what you're doing and simply following a tun tutorial, you will be fighting to setup TAP but not because it's more difficult but because you don't know what you're doing. Which easily can lead to network conflicts in a TAP environment and then it looks like it's more complicated.

fact is, if you don't need a tutorial because you know what you're doing, setting up tap takes as much time as setting up tun.

with tap there are many solutions about subnetting, i found myself the easiest way is to use a class B subnet. site1 (Network1) using site2(network2) using site3 using etc.

you setup site1 with the oVPN server and to give clients the ip range - so you can have over 200 ovpn clients (subnets) each subnet can have over 200 clients in itself. Makes a total of 40.000 clients you can handle (doubt oVPN can handle that but as you see, setting up proper subnetting will give you more then enough as you most likely ever need)

you use a tap and all clients are together as in a huge corporate network.

IF, however each site has it's own DHCP, and it should have, you need to make sure using ebtables or iptables or dnsmasq to block dhcp distribution to go wild. ebtables however will slow down the performance. using dnsmasq dhcp-host=20:a9:9b:22:33:44,ignore for example will be a huge task to setup on all dhcp servers. however, on modern hardware the impact of ebtables isn't that big. only 1 or 2 %

the overhead of the tap, roughly 32 to the tun, isn't that much a problem either (might be on unencrypted networks) but on encrypted networks it's usually the AES that will cause the slowdown.

On my wrt3200acm for instance unencrypted I get 360Mbps. Using encryption it goes down to 54-100Mbps depending on what kind of encryption I choose) but openvpn doesn't do encryption on 1500 and a 2nd encryption on the 32 overhead. Instead it does a 1 time encryption on 1500+32overhead.

So the impact here is minimal.

On older hardware you might notice the impact more, but on modern hardware it's really down to the minimum.

Encryption between 2 virtual machines with AES support gets me my ovpn with TAP to 120-150Mbps.

Some report dedicated routers WITH AES hardware encryption support getting as high as 400Mbps! 3 times faster then a i5-3570k can do (which on my test system couldn't get higher then 150Mbps at 100% of 1 core utilization) My other end: E3-1231 v3, then was roughly at 7% CPU utilization, around 25% of the core openvpn was using was utilized. So the E3 most likely could increase the connection by 3 to 4 times.

so you'd have something between 360Mbps and 600Mbps with a connection between E3-1231 v3 cpu doing tap AES265 cipher, auth SHA256 and ta.key, certificates tls-cipher I also used the highest TLS-DHE-RSA-WITH-AES-256-SHA256

To point this out, with tap: wrt3200acm gets up to 70-80mbps with encryption. i5-3570k gets to 120-150 with encryption. E3-1231 v3 gets at least 360Mbps with encryption (this is interpolated from my findings with case 1 and 2 because I didn't have 2 E3-1231 v3 to test with.)

These are my findings based on windows to windows copying between 2 clients in 2 different subnets connected by openvpn TAP

  • I like the info provided here, but that was a bit too much to tell "he does not know what he is doing". I also find configuring TAP not hard, because I know what to do after reading really a lot about networking. Nevertheless that was not easy at all to get all information together to get TAP to work properly. Even configuring TUN with the proper route table if needed can be tricky if someone is newbie. What I want to say is, I would not discourage the people, but rather I would motivate by providing some links necessary to get a full understanding what to do and how to use this info Commented Aug 30, 2021 at 7:57

I had this same question years ago and attempted to explain it in straightforward terms (which I personally found lacking in other resources) on my blog: An OpenVPN Primer

Hope it helps someone

  • 3
    Whilst this may theoretically answer the question, it would be preferable to include the essential parts of the answer here, and provide the link for reference. Commented Apr 8, 2015 at 19:28
  • Great post! I rarely read a whole post like this but this one I did. I agree with Mark Henderson though, you should write a small summary and put the link after. Commented Jul 7, 2015 at 1:46

I usually default to TUN as having it in it's own subnet is better for a variety of reasons, among which firewalling, and OpenVPN basicly works out of the box like this.

TAP has several advantages though, among which is that connected clients behave exactly like physical ones. This means that for example any ip restricted resources that are normally only available in the physical network also work.

Another use case I see in home situations is that the OpenVPN server has no internet facing side and thusly routes through some sort of provider supported modem/router. More often then not these don't support things like static routing which is a must if you let OpenVPN use it's own subnet.

  • Use of tap makes bridging possible, but doesn't require it. You may setup tap VPN which still uses a dedicated subnet. Commented Nov 9, 2021 at 6:33

If then, why what, how much have you got? I would utilize TAP, explicitly for the reason that the layering of the packets proceeds with much less latency and loss of transmission which is abated with this method. However only with layer 3 does this affect any apparent effect on the operation of the VPN, notably the tunneling aspect and which IPs are allowed through and assignable addresses. The use of UDP possibly introduces another situation where you would need to decide which is the best route to take for you. Each network is different and requires a unique set of parameters. Hope this helps.

  • 1
    Quite confusing. Please consider cleaing it up, explaining the differences that matter and keying off them.
    – vonbrand
    Commented Jun 25, 2014 at 20:03

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .