[Babel-users] Fwd: Why we switched to Babel

[Saverio Proto]

So why they switched to babel ?
babel makes some magic with MTU ?

I dont see the end of the story.
Il 08/ago/2015 04:47, "Jenny Ryan" <tunabananas at gmail.com> ha scritto:

> ---------- Forwarded message ----------
> From: "Marc Juul" <juul at labitat.dk>
> Date: Aug 6, 2015 9:58 AM
> Subject: Why we switched to Babel
> To: "Jenny Ryan" <tunabananas at gmail.com>
> Cc:
>
> When people share their internet we use a tunnel to hide their IP (and to
> connect them to the mesh through the Internet). This tunnel takes a few
> bytes of overhead. All physical connections, whether they're ethernet, wifi
> or even an abstraction like a tunnel, have an MTU (Maximum Transfer Unit)
> which is the size of the largest packet that can be sent over the
> connection. Normally the MTU is 1500 but since the tunnel needs a few bytes
> for overhead the MTU of the tunnel will be less than 1500.
>
> When people connect to the wifi network called peoplesopen.net they will
> connect with an MTU of 1500 since this is the default for wifi. We need a
> way to tell them that the MTU is actually less than 1500. In an IP network
> (which is at layer 3) there is a built-in system for dealing with this. If
> any router receives a packet larger than what it can pass on through the
> next connection (in this case through the tunnel) it can report back to the
> client using the ICMP protocol (a companion protocol to IP, and the
> protocol used for ping) that the packet was too big and the client can then
> adjust its MTU accordingly.
>
> For batman-adv, because it is a layer 2 protocol, we don't have this
> system available. We tried different tactics such as using DHCP to tell the
> clients the MTU they should use, but it turns out that many operating
> systems completely ignore this. We tried something called TCP MSS clamping,
> which is a bit of a dirty hack, but that only works for TCP, which is a
> problem since UDP is widely used for e.g. VOIP, video streaming, gaming,
> torrenting, etc.
>
> Even combining the different tricks we still had a problem where some
> operating systems would get in trouble if they tried to send large UDP
> packets. We had a moment where we realized that the only types of common
> communication that wouldn't work on this mesh would be torrenting and video
> streaming from windows computers, and joked about that being a feature
> instead of a bug :) but in the end we switched to Babel.
>
> There was another reason: In batman-adv the MAC address is the identifier
> used for each device. It is possible to configure many devices to randomize
> their MAC address but it needs the user to do something, so most people
> will never know to do it. Having the MAC address as the identifier makes it
> pretty easy for anyone to track anyone else as they move about the city, as
> long as they know the MAC address of e.g. their phone, which it is easy to
> discover if you are ever in the same room with them, just by listening to
> network traffic. We had some ideas for how this could be fixed, but the
> potential solutions we came up with were never satisfactory.
>
> For mesh, each time a user connects to a new node they get a new IP
> address. In the future we may implement roaming support which will let
> people keep their IP as they move around the city, but it will still switch
> after e.g. 10 minutes, so tracking people becomes much harder.
>
> That's a lot of text, but eh it's a complicated issue. It sounds like
> you're having many late night conversations. Hope it is enjoyable!
>
> --
> marc/juul
>
>
>
>
> _______________________________________________
> Babel-users mailing list
> Babel-users at lists.alioth.debian.org
> http://lists.alioth.debian.org/cgi-bin/mailman/listinfo/babel-users
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.alioth.debian.org/pipermail/babel-users/attachments/20150808/166b5cbb/attachment.html>