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

Dave Taht dave.taht at gmail.com
Sun Jan 25 00:02:50 EST 2015

On Sat, Jan 24, 2015 at 8:35 PM, David Lang <david at lang.hm> wrote:
> On Sat, 24 Jan 2015, dpreed at reed.com wrote:
>> On Thursday, January 22, 2015 1:19pm, "Richard Smith"
>> <smithbone at gmail.com> said:
>>> On 01/22/2015 04:18 AM, David Lang wrote:
>>> >> Recently, we picked up the 11th floor as well and moved many people up
>>> >> there. I got a 3rd AP (another TP-Link AC1750) and set that one up on
>>> >> a free channel with a different ESSID.
>>> >
>>> > I like to put all the APs on the same ESSID so that people can roam
>>> > between them. This requires that the APs act as bridges to a dedicated
>>> > common network, not as routers.
>>> That's the ultimate plan but for convenience of being able to easily
>>> select what AP I'm talking to or to be able to tell folks to move from
>>> one to another I've got them on different ESSIDs. It also helps me keep
>>> track of what RF channel things are on.

My usual use case for using different APs is to find an error in the campus.

When someone tells me that "Lupin-lodge" is down, I know exactly which machine
to check. If everything was named Lupin, I'd have to check far more
than one AP, and
to ask approximately where on the campus they were.

>> 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.

I am under the impression that network-manager and linux, at least,
tend to renegotiate
IPv6 addresses on an down/up, and preserve ipv4.

> Bridgeing allows the connections to remain intact. The wifi stack
> re-negotiates the encryption, but the encapsulated IP packets don't change.

While I actually agree with dlang on having all the same ssid and
bridging, and not routing, on a conference, as well as with the idea
of disabling broadcast (and I assume direct connectivity between two
people seated side by side), it is a pita:

More than once I've wanted to share a git tree with someone right next
to me. I try to hand them my ip to grab the tree, and they can't even
ping me, so I end uploading it somewhere, and he or she downloading it
from there. Similarly, breaking interconnectivity precludes sane usage
of in-conference

In my case, since choosing to live in a routed, rather than bridged
world, I have modified the nailed up tools I use to be more
connectionless. Instead of ssh (tcp), I use mosh-multipath (udp),
which is far superior for interactive shells in lousy wifi
environments. For vpns, I switched to tinc, which will attempt direct
connections over udp, and tcp on both ipv4 and ipv6. For access to
google, I adopted quic in my chrome browser. Since doing all these
things I rarely notice losing a nailed up connection or migrating from
AP to AP. Additionally I use babel (where I control the network) and
ad-hoc wifi to transparently migrate from AP to AP, and (often) from
AP to wired to AP to wired as I change locations, also with no loss in

I don't expect the scale userbase to have made these adjustments in behavior. :/

> I do this with the wifi on it's own VLAN (actually separate VLANs for 2.4
> and 5GHz) and have the APs configured not to relay broadcast traffic from
> one wireless user to another. This cuts down a LOT on the problems of
> broadcasts.
> In about a month I'm going to be running the wireless network for SCaLE
> again, and I would be happy to instrament the network to gather whatever
> info anyone is interested in. I will be using ~50 APs to handle the ~2800 or

I will look into some tools bismark and others have.

Will you attempt to deploy ipv6?

> so devices that show up, with the footprint of each AP roughly covering a
> small meeting room (larger rooms have 2 APs in them, the largest room has 3,
> and I'm adding APs this year to cover the hallways better because the ones
> in the rooms aren't doing well enough at the low power settings I'm using)

I am of course interested in how fq_codel performs on your ISP link, and
are you planning on running it for your wifi?

> David Lang
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Dave Täht


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