[mesh-dev] We need to talk about batman

[Mo Balaa]

+1 for abandon the idea of meshing at layer 2

On Friday, October 17, 2014, Alexander Papazoglou <papazoga at gmail.com>
wrote:

> Hello mesh-dev.
>
> I think we may finally have an explanation of the vexing issue of "I can't
> connect to the internet over peoplesopen.net."
>
> Marc and I spent some time staring at wireshark dumps and  thinking
> about why some clients are unable to consistently connect via the
> tunnel last night. I think Marc came up with a disappointing but correct
> answer: it is basically an mtu issue (mtu is not being discovered
> correctly), BUT there is no good fix because we are tunneling at layer 2.
>
> When a packet arrives at a node from a client with too large an mtu,
> what SHOULD happen in a normal forwarding situation (per RFC 1191)
> is that the node issue a ICMP "Destination Unreachable" packet with a
> "Fragmentation required" code. The client then uses this information to
> reset its mtu.
>
> This doesn't happen because we aren't really forwarding (forwarding happens
> at layer 3). Instead, our interfaces (open0 and bat0) are bridged. So if a
> frame
> coming from open0 doesn't fit into bat0 it most likely gets silently
> dropped.
>
> So bridging open0 with bat0 is a disaster. A quick fix might be to replace
> bridging with forwarding (at the IP level). I suspect this is not the
> right thing
> to do. It might be better to abandon the idea of meshing at layer 2; there
> are numerous advantages to this.
>
> In any case; we should discuss options this Tuesday.
>
> Alex
>
>
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