Re: [Cerowrt-devel] Recording RF management info _and_ associated traffic?

[dpreed@reed.com]

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Disagree. See below.


On Saturday, January 24, 2015 11:35pm, "David Lang" <david@lang.hm> said:



> On Sat, 24 Jan 2015, dpreed@reed.com wrote:
> > A side comment, meant to discourage continuing to bridge rather than route.
> >
> > There's no reason that the AP's cannot have different IP addresses, but a
> > common ESSID. Roaming between them would be like roaming among mesh subnets.
> > Assuming you are securing your APs' air interfaces using encryption over the
> > air, you are already re-authenticating as you move from AP to AP. So using
> > routing rather than bridging is a good idea for all the reasons that routing
> > rather than bridging is better for mesh.
> 
> The problem with doing this is that all existing TCP connections will break when
> you move from one AP to another and while some apps will quickly notice this and
> establish new connections, there are many apps that will not and this will cause
> noticable disruption to the user.
> 
> Bridgeing allows the connections to remain intact. The wifi stack re-negotiates
> the encryption, but the encapsulated IP packets don't change.


There is no reason why one cannot set up an enterprise network to support roaming, yet maintaining the property that IP addresses don't change while roaming from AP to AP.  Here's a simple concept, that amounts to moving what would be in the Ethernet bridging tables up to the IP layer.
 
All addresses in the enterprise are assigned from a common prefix (XXX/16 in IPv4, perhaps).  Routing in each access point is used to decide whether to send the packet on its LAN, or to reflect it to another LAN.  A node's preferred location would be updated by the endpoint itself, sending its current location to its current access point (via ARP or some other protocol).   The access point that hears of a new node that it can reach tells all the other access points that the node is attached to it.  Delivery of a packet to a node is done by the access point that receives the packet by looking up the destination IP address in its local table, and sending it to the access point that currently has the destination IP address.
 
This is far better than "bridging" at the Ethernet level from a functionality point of view - it is using routing, not bridging.  Bridging at the Ethernet level uses Ethernet's STP feature, which doesn't work very well in collections of wireless LAN's (it is slow to recalculate when something moves, because it was designed for unplug/plug of actual cables, and moving the host from one physical location to another).
 
IMO, Ethernet sometimes aspires to solve problems that are already well-solved in the Internet protocols. (for example the 802.11s mess which tries to do a mesh entirely in the Ethernet layer, and fails pretty miserably).
Of course that's only my opinion, but I think it applies to overuse of bridging at the Ethernet layer when there are better approaches at the next layer up.

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