Hi!
Comments?
Mitar
---------- Forwarded message ---------- From: Jenny Ryan tunabananas@gmail.com Date: Fri, Aug 7, 2015 at 11:41 PM Subject: [Babel-users] Fwd: Why we switched to Babel To: babel-users@lists.alioth.debian.org
---------- Forwarded message ---------- From: "Marc Juul" juul@labitat.dk Date: Aug 6, 2015 9:58 AM Subject: Why we switched to Babel To: "Jenny Ryan" tunabananas@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@lists.alioth.debian.org http://lists.alioth.debian.org/cgi-bin/mailman/listinfo/babel-users
regarding MACs, would it be possible for batman-adv to use hashed MACs?
On 08/08/2015 11:51 PM, Mitar wrote:
Hi!
Comments?
Mitar
---------- Forwarded message ---------- From: Jenny Ryan tunabananas@gmail.com Date: Fri, Aug 7, 2015 at 11:41 PM Subject: [Babel-users] Fwd: Why we switched to Babel To: babel-users@lists.alioth.debian.org
---------- Forwarded message ---------- From: "Marc Juul" juul@labitat.dk Date: Aug 6, 2015 9:58 AM Subject: Why we switched to Babel To: "Jenny Ryan" tunabananas@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@lists.alioth.debian.org http://lists.alioth.debian.org/cgi-bin/mailman/listinfo/babel-users
On Saturday, August 08, 2015 23:51:42 Mitar wrote:
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.
What spoke against using the batman-adv layer2 fragmentation: http://www.open-mesh.org/projects/open-mesh/wiki/2012-09-24-GSoC-2012-Martin... ?
Cheers, Marek
b.a.t.m.a.n@lists.open-mesh.org
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Marek Lindner -
Mitar -
Moritz Warning