Difference between a loopback device and tun/tap device.

dE_logics · Advocate Joined: 02 Jan 2009 Posts: 2253 Location: $TERM

One requires a module and one does not? I can have many tun/tap devices and just one loopback?

Another question -- on the tun/tap device, the server/daemon/kernel will listen for incoming connections on an IP which the virtual interface. The client will connect from the same interface and have the same source IP? e.g.

A packet is received by the kernel from a userspace application, it's source = 192.168.2.1 and destination = 192.168.2.1.

Am I missing something?
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eccerr0r · Posted: Mon Sep 09, 2013 5:35 pm Post subject:

Not sure what you're asking here, they are kind of different...

Loopback points back to the same machine you're on...

TUNnel/TAP "wires into" a network interface so you can add/extract packets into the interface, and they can lead out of the machine (but not always necessary)...

You can have many taps/tunnels. But you can only be yourself (though 127.x.x.x all are loopback, so you have 16 million loopback addresses minus broadcast...)

I had a UML virtual machine using tun/tap (creating a tap). It had an external IP address. People could connect to it from the outside world and connections from with the VM shows up as the external address. If I connect from it to the machine the VM is hosted on, it shows up as its own IP address.

This isn't the only use for tun/tap, can create software tunnels for VPNs as well so packets going through will go through software before sent back...

Maybe this is more confusing now. hmm.
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dE_logics · Advocate Joined: 02 Jan 2009 Posts: 2253 Location: $TERM

Ok, so the main thing is bridging to a real interface which cannot happen (?) with a loopback device. But bridging requires tap exclusively.
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666threesixes666 · Posted: Tue Sep 10, 2013 3:55 am Post subject:

out of curiosity, what tap/tun method are you using, openvpn?

eccerr0r · Posted: Tue Sep 10, 2013 3:11 pm Post subject:

You can bridge interfaces together but a tap is associated with an interface.

What are you trying to do here, I guess that'd be interesting information.

Currently for me:

I use virtual network interfaces for my virtual machines and bridge them together. You make a bridge and then attach the physical/virtual interfaces to it.

On another machine I use tun/tap with openvpn that opens software tunnel interfaces that will encrypt and send out packets...
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dE_logics · Advocate Joined: 02 Jan 2009 Posts: 2253 Location: $TERM

"Method"? I'm using ip command (iproute2) to create the interfaces.

@eccerr0r
Purpose is same as yours -- Advanced networking with Qemu -- I'm learning that right now.

But tun device doesn't have level 2, and bridging requires handling of frames and ARP.
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eccerr0r · Posted: Wed Sep 11, 2013 5:43 am Post subject:

Apparently QEMU virt-manager made it really easy, except networkmanager does not support bridges.

This is what I did:

I got rid of networkmanager.

I setup enp4s0 (my onboard ethernet) to be enabled but not get an ip address
I setup br0 with a bridge connection to enp4s0
I setup br0 to get an IP address.
/etc/conf.d/net

dE_logics · Advocate Joined: 02 Jan 2009 Posts: 2253 Location: $TERM

Thanks. In Qemu networking I'll take this into reference.
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