Re: WDS ping

From: Eric Enockson (
Date: 2002-03-04 17:58:49 UTC

On Mon, Mar 04, 2002 at 12:13:08AM -0800, Kristian Hoffmann wrote:
> We used to bridge our wireless network which included 7 T1s and ~10 access
> points. The amount of broadcast traffic being generated and needlessly
> broadcast over the wireless portion of our network was disgusting.
> Instead of playing with BREPF (Bridged Ethernet Packet Filtering, I
> think), we decided to do something that didn't crash our routers on a
> regular basis. Routing. It was/is a painful process to switch but it was
> worth it in our case. And yes, dhcp relay agents play an important part
> in making that work. There was a definite advantage to bridging in the
> beginning. But as the network got larger it's drawbacks became very
> visible. I have to appologize for being so negitive towards bridging but
> I wasted a lot of valuable time trying to get WDS to work before giving up
> on it.

        So you are down on the whole

ethernet <--> WDS <--> WDS <--> WDS <--> ethernet

        802.11 distribution systems extended service sets thing. Fair enough. It sound like it didn't work out in your case and i'm wondering if it won't in any.

        However i've had this argument with some of the other seattlewireless guys and finally started looking at it from the point that all those smart guys making the 802.11 spec didn't plan all these bridges and extended service sets for nothing. Possible they weren't believing in real time routing table updates or a grand ipv6 implementation, but when you have mobile(not portable) 802.11 clients and are fantasizing about making your own telco network as the portland guys are(please don't flame if i'm wrong, not involved in that in anyway just have read a bit of the website and found it a tremendous resource) you have to support mobile users walking from one ap to another.

        Could you have routing tables on those ap's and update them in realtime? Ah at some point you have to bridge the pkts cause you won't know where the f-er is headed. Have you seen some of the mobile phone users cracked out wandering the west end yelling at their girl/boy friends.

        So in your case bridging and 802.11 distribution systems didn't scale but with mobile users in the wireless world you will have to bridge pkts to ap's around a mobile user, and appear to the LLC tcp/ip level as one large network???(thinking out loud) 
        Interaction with other IEEE 802 layers IEEE 802.11 is
required to appear to higher layers [logical link control (LLC)] as a current style IEEE 802 LAN. This requires that the IEEE 802.11 network handle station mobility within the MAC sublayer. To meet reliability assumptions (that LLC makes about lower layers), it is necessary for IEEE 802.11 to incorporate functionality that is untraditional for MAC sublayers.

        Also maybe when ipv6 is implemented everwhere these parts of the 802.11 spec will become obsolete but until then i'm thinking implementing the full spec will be usefull for something, and doing that on linux acccess points would rock!  

The only case I can think of where bridging is absolutely
> necessary is if you want to run PPPoE over a multiple wireless networks
> linked together. I don't think there is any way to route ppp packets
> unless you somehow manage to do PPPoEoIPoE. :P
> -Kristian
> On Sun, 3 Mar 2002, Jim Thompson wrote:
> >
> > On Sun, Mar 03, 2002 at 03:20:04AM -0600, Jim Thompson wrote:
> > >
> > > I'd love to look at the code. Routing isn't *always* possible.
> > >
> > > Jim
> >
> > Could you name some your top instances of this?
> >
> > The main one is 'wireless extension'.
> >
> > ethernet <--> WDS <--> WDS <--> WDS <--> ethernet
> >
> > One in particular i'm thinking of is where i have an antenna
> > shooting into a coffee house down the street, and want to put an openap
> > in there, but have my dhcp server in my apartment. So forwarding dhcp
> > requests from openap to smc(prism2 card) card in pc sitting by window
> > is what i desire. I have set up an openap and am getting familiar
> > with what it can/can't do. Possibly i could forward the request via
> > routing foo or the linux regular ethernet bridging but then the only
> > device i'm going to have is the prism card in the openap so probably
> > i'm stuck with WDS 802.11 foo, but still figuring.
> >
> > In this instance you can run a DHCP relay on the openap box inside the coffee shop,
> > and have the dhcp server in your apartment service the requests.
> >
> >

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