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Why Wireless Activity when Wired?

Discussion in 'Tomato Firmware' started by noob_for_life, May 28, 2008.

  1. noob_for_life

    noob_for_life Addicted to LI Member

    have a WRT54GL set up as a wireless bridge with Tomato v1.07. One of my servers is connecting to it via ethernet and then, wirelessly, to the rest of our network. Sometimes, I'll back up a laptop to a drive on this server. I'll plug in the laptop to one of the ethernet ports (and shut off the laptop's wireless network) and then start the backup.

    When I do, the wireless light on the WRT54GL goes on and stays solid. Doesn't this mean it is using network bandwidth even though both computers are connected to it? Assuming so, why does it use this bandwidth. Shouldn't it route between the two wired connections?

    Thanks, Gary
  2. HennieM

    HennieM Network Guru Member

    The key word here is "bridge". Now I'm not 100% on this, but what I think is this:

    There is a funny with WET mode, in that the WET device seems to proxy arp for anything connected to the wireless side of it. My opinion therefore is that your wired ports and wireless interface are "dumb" bridged in WET mode, which means that whatever comes in the one end, must go out on all other ends, like the hubs of old.

    I may be (and probably are) wrong... ;)
  3. noob_for_life

    noob_for_life Addicted to LI Member

    Thanks. That seems sensible. To avoid this, I should test it with a small router wired into the bridge?
  4. fyellin

    fyellin LI Guru Member

    Even when used as an AP, does the tomato firmware act as a switch or a hub? I.e. does it keep track of which devices are where, or does it just send everything destined for the LAN over both wired and wireless?

    When I look at http://<my router>/advanced-routing.asp, I see: * 0 br0 (LAN)

    This leads me to believe that all LAN traffic is sent to br0, which bridges the wireless ethernet port and the LAN wired ports. Perhaps there is some internal smarts that is not user-visible, though.
  5. HennieM

    HennieM Network Guru Member

    @noob: I would think the best way to test is to sniff the wireless while you have wired-only activity.

    @fyellin: The switch (the 5 ethernet connectors) on a WRT is an intelligent/managed switch, with 4 of them normally bridged to interface br0. When used as a router, AP, and even a WDS node, the wireless interface is joined with the 4 physical ports of the switch into the br0 interface, but this bridge/switch never functions like a hub; i.e. every port, whether it's an ethernet port or the wireless port, just pass traffic from the source to the destination port.

    NB! This happens on the OSI layer 3 level (I think it's called the MAC layer). The IP routing you see " * 0 br0 (LAN)" is on level 4, i.e. the IP level, and has nothing to do with the layer 3 handling of traffic to individual physical ports.

    In WET (Wireless Ethernet Bridge) mode however, I suspect the bridge (br0) is set to "hub" or semi-hub mode, re-transmitting everything that comes in on one port to all the other ports on layer 3, whether it's IP traffic or not. As mentioned, I may be wrong.
  6. fyellin

    fyellin LI Guru Member

    Thanks for the clarification. I'm glad to know that the router is smart enough to do the right thing.

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