Does DLink DWL-G810 bridge networks?

Discussion in 'Wireless Internet' started by John ., Oct 7, 2004.

  1. John .

    John . Guest

    From the DLink documentation I can't determine if the DWL-G810 bridge
    can be used to interconnect 2 wired Lans into one?

    I know the DWL-2100AP+ can do this.

    But the DWL-G810 looks like it is used to support just ONE device.
    Does anyone know if it will pass ALL ip's across the bridge from/to
    the two lans?
    John ., Oct 7, 2004
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  2. John .

    Guest Guest

    I have 4 of the 2100 setup as a bridge and they kick but. The 4 houses are
    about 3 - 4 miles from the main 2100 AP. All are connected to antennas on
    there roofs.

    Were going to be adding some more houses soon with more 2100's.

    Digital D
    Guest, Oct 8, 2004
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  3. No. One device, one MAC address, and one badly written data sheet.
    Bridges don't know what to do with IP addresses, which run on Layer 3.
    Bridges work on Layer 2, which are MAC addresses. The DWL-G810+
    apparently (i.e. not absolutely sure) looks like a simple client-end
    wireless bridge which will pass exactly one MAC address. This is in
    contrast to the WET11, DWL-900AP+, DWL-2100AP+, and WAP11, which will
    pass about 32 MAC addresses.

    This is about the WET11 but might help explain the problem:

    Different types of wireless bridges:
    I don't agree with their definitions and names, but I think you can
    see the problem. There are a sufficiently wide variety of types (and
    names) of wireless bridges to confuse anyone. If I get ambitious and
    find some time, I'll scribble a web page with my names for the various
    types of wireless bridges, which should add to the confusion.
    Jeff Liebermann, Oct 8, 2004
  4. John .

    Bob Alston Guest

    What antennas are you using on the rooftop 2100s that connect 3-4 miles

    Bob Alston, Oct 8, 2004
  5. John .

    John . Guest

    Maybe I misstated my question, but wouldn't ONLY ONE mac address be
    passed between two DWL-G810's, the mac of the bridge? Even though
    each wired LAN in two separate buildings has 5 or 6 PC's, wouldn't two
    DWL-G810's just be passing traffic to/through the other corresponding

    DWLG810--pc1--pc2--pc3==>switch (all cat5e)
    DWLG810--pc4--pc5--pc6==>switch (all cat5e)

    Does this work?
    John ., Oct 8, 2004
  6. Nope. The problem is the type of bridge. Again, I'm guessing that
    the DWL-G810+ is a "imple bridge and not a transparent bridge. It's
    difficult to tell from the data sheet. The difference is that a
    simple bridge only deals with one MAC address, while the transparent
    bridge or "network bridge" is designed to connect two networks
    together as in your ascii drawing.

    Reminder: bridges deal with MAC addresses, not IP addresses. Let's
    start with a wired LAN bridge. (Incidentally, a switch is a bridge
    with more than 2 ports.) The wired bridge builds a table of MAC
    addresses that it hears on each port. It looks something like:
    Address Port
    MAC1 1
    MAC2 2
    MAC3 1
    MAC4 2
    MAC30 2
    MAC31 1
    For convenience I decided the odd MAC addresses would be plugged into
    port 1, while the even MAC addresses in port 2. The 802.3 ethernet
    MAC address header includes the source and destination MAC address of
    each packet. The source address is used to populate the table, while
    the destination address is used to determine which port it needs to

    bridging decision time:
    1. If the destination MAC address is in the bridge table, the packet
    crosses the bridge.
    2. If the destination MAC address is in the bridge table, but on the
    same port as the originating MAC address, the packet does NOT cross
    thr bridge (because it has nowhere to go).
    3. If the destination MAC address is NOT in the bridge table, it is
    assumed to be local traffic and does NOT cross the bridge.
    4. If there is no destination MAC address, as in a broadcast packet,
    then the traffic crosses the bridge.

    Remember, the whole idea of a bridge is to reduce network (or
    wireless) traffic.

    With a two port bridge, such decisions are fairly trivial in that all
    that needs to be decided is whether to cross or not to cross. With a
    switch (more than 2 ports), a decision as to which port needs to be
    made. A bridge or switch also needs a little time to make the decode
    the header and make a decision, so some buffering (FIFO) is usually
    added to each port.

    I'm going to ignore the added complexities of a VLAN, spanning tree
    algorithm, and WDS repeaters.

    Now we introduce a wireless bridge. Let's start with the "simple
    bridge" and it's one MAC address. The last thing you want is for
    every last lousy packet on your LAN to go out the wireless port on
    your router and pollute the airwaves with useless traffic. The simple
    wireless bridge works exactly the same way as the wired LAN bridge
    exept that it's only concerned about traffic to one computah. The
    access point has a table of radio MAC addresses and makes a decision
    if the packet has a destination at the other end of the wireless
    bridge. Multiple simple bridges are not a problem as the table can
    have multiple "ports" or radios. This is the way all of the common
    wireless access points and client radios operate. A wireless access
    point should really be called a wireless switch.

    Just one problem. Each client radio only passes one MAC address to
    the access point. If you build a network of PC's behind the client
    radio, the wireless access point cannot determine if a given packet is
    destined for any of these computahs because the access point MAC
    address table only has one table entry for the client radio.

    To connect two networks together, a wireless transparent bridge is
    needed. It's exactly the same as a wired bridge, with its MAC address
    table, except that the table is now duplicated at each end of the
    bridge. Every time a new MAC address appears on one end of the
    bridge, the information has to be added to the table on the other end.
    The protocol for doing this is proprietary by manufacturer, which is
    why mixing different radio types is a bad idea. The size of the MAC
    address tables is also limited in many bridges. The cheapo bridges
    are 31 MAC addresses, while the fancy one's (Proxim, Alvarion) can
    handle about 2000 or more.

    So, why can't you just take two access points, aim them at each other,
    and use them to bridge two networks? Well, they can but they lack
    support for duplicating the bridge table entries at each end. All the
    hardware and most of the software is there, but without a bridging
    table protcol, the common access point can only deal with one MAC
    address per radio.

    That leaves us with your original question, which reduces down to why
    can't I pile a bunch of MAC addresses behind a simple bridge (client
    radio) and use it to connect two LAN's together though a single MAC
    address? You could if the access point was able to store MAC
    addresses for the destination PC's. 802.11 will encapsulate the 802.3
    ethernet packets. The bridge will see only one of the encapsulated
    MAC addresses, and only one computah will be able to communicate.
    Were it not for the encapsulation of MAC addresses, it would be

    I'm not sure how the "game adapters" and other bridges handle the
    multiple computahs. My guess(tm) is that they expose the encapsulated
    source MAC address in the 802.11 header, which makes the traffic look
    like multiple client radios. The common access point can easily
    handle multiple radios. Again, I'm not sure about this and need to so
    some wireless sniffing to be sure (yet another project).
    Jeff Liebermann, Oct 9, 2004
  7. John .

    John . Guest

    Jeff, thanks for your complete exhaustive explanation. It really
    really too bad that manufacturers don't more fully explain their

    My goal was to replace an older pair of DLink DWL-900+ (b mode)
    bridges operating in one to one bridge mode. It was fine
    interconnected two small wired lans (about 4 PC's each) into one
    network neighborhood.

    I just replaced the DLink's with a pair of Netgear WGE101 (g mode)
    bridges. To get the Netgear bridges to work, I had to set them to
    ad-hoc mode with WEP security.

    It's working, but I have an uncanny feeling it's not a true
    transparent bridge. I could easily see all the shared folders from
    both lans, but had trouble with Internet access through the
    router/switch that is on one LAN only.

    There's very little setup with the Netgear, so it's hard to see what's

    BTW, qcheck throughput went from about 4.5 mbps actual throughput, to
    11-12 mbps actual throughput.

    Except for the ad hoc mode strangeness, it seems to work.

    John ., Oct 10, 2004
  8. Yep. Last month I attended a meeting where such things were
    discussed. The consensus was that advanced technical data would
    "confuse" the typical customer and would be detrimental to sales. My
    past experience confirms this effect. The more technobabble included
    in the sales and installation literature, the more problems. If the
    goal were to keep the support phone from ringing, most manufacturers
    would supply zero technical information. Sorry.
    The DWL-900AP+ does 22Mbits/sec quite reliably if you turn off the 4x
    (bottom of page). The Rev C incantation will do 802.11g speeds.
    Unfortunatly, both will only bridge 31 MAC addresses. That's fine for
    4 PC's at each end. I have several pairs of these at customers.

    Dumb question: Why would you wanna replace a wireless bridge with one
    that offers no additional features or improvements? More
    specifically, what problem are you trying to solve?

    I guess that's correct. A point to point bridge sorta kinda operates
    in ad-hoc mode. You would use the infrastructure mode if you had a
    central access point connected to an internet connection and a bunch
    of random client radios accessing the internet through it. However,
    for a point to point transparent bridge, ad-hoc should work.

    I just slogged through the manual at:
    Well, at least it has a signal strength indicator. Unfortunately, it
    doesn't have a display of a bridging table to see who's connected.
    However, it doesn't look like a typical wireless transparent bridge
    (such as the DWL-900AP+). For example, there's no way to filter by
    MAC address, manually set the exact speed, or deliver SNMP traps or
    alarms. No WPA encrytion. No clue how many MAC addresses it can
    bridge. I wouldn't call this box much of an improvement. It would
    make a nice "game adapter" but I suspect it might be lacking for
    bridging two networks. (Disclaimer: I haven't played with it so I may
    be totally wrong).
    What kind of trouble? Be specific.

    If it's a real live genuine trasparent bridge, then methinks you
    should be able to ping all the IP addresses on the other side of the
    bridge, and then immediately run:
    arp -a
    to display the MAC address table showing BOTH sides of the bridge. I
    don't have an easy way to test this right now, but suspect that it
    should be possible. If it's a single MAC address simple wireless
    bridge, you'll only see the MAC address of the bridge radio from the
    far end.

    Another way to describe the operation of a transparent wireless
    ethernet bridge is that it should operate EXACTLY as if an ordinary
    ethernet switch box were inserted in place of the two wireless bridge
    That's intentional. The more you know, the more questions you'll ask,
    and the more you'll complain. Can't have that happen. What's scarey
    is that some of these boxes have well hidden VTAM diagnostic ports the
    belch LOTS of information (if you grok hexadecimal). It gets used
    during development and troubleshooting, but remain inaccessible to the
    customers. You can often find a the connector in the block diagrams
    on the FCC ID web pages or just by snooping around the board.
    Something like this:
    Distance? Antennas? I'm getting about 10-12Mbits/sec thruput with
    pairs of DWL-900AP+ bridge radios using mostly 8dBi patch antennas at
    ranges between 150ft to 1500ft. However, I had to disable the flakey
    4x mode to make it happen. I woudn't give up on the DWL-900AP+ radios
    quite yet.

    Oh, if you're using external antennas with pigtails, there a real
    problem with the SMA plugs not bottoming properly on the DWL-900AP+
    panel mounted SMA receptacle. Unscrew the SMA nut, remove the gold
    lockwasher, and replace the nut. The connector will now fit snuggly.
    In this case, all ad-hoc means is that there's no controlling access
    point to deal with cts/rts flow control and system management.
    Jeff Liebermann, Oct 10, 2004
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