How do you bridge one ethernet and not the other? - Networking

This is a discussion on How do you bridge one ethernet and not the other? - Networking ; I have a Linux computer that sits in my living room and speaks over a wireless network with WPA using wpa_supplicant. That works fine. This computer also has an ethernet card in it. I'd like to connect another device into ...

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Thread: How do you bridge one ethernet and not the other?

  1. How do you bridge one ethernet and not the other?

    I have a Linux computer that sits in my living room and speaks over a
    wireless network with WPA using wpa_supplicant. That works fine. This
    computer also has an ethernet card in it. I'd like to connect another
    device into that ethernet with a crossover cable and let that other
    device use DHCP to get an address from my DHCP server (which is on the
    other side of the wireless network). Do I set that ethernet card up as a
    bridge? If so, how?

  2. Re: How do you bridge one ethernet and not the other?

    Scott Simpson wrote:
    > I have a Linux computer that sits in my living room and speaks over a
    > wireless network with WPA using wpa_supplicant. That works fine. This
    > computer also has an ethernet card in it. I'd like to connect another
    > device into that ethernet with a crossover cable and let that other
    > device use DHCP to get an address from my DHCP server (which is on the
    > other side of the wireless network). Do I set that ethernet card up as a
    > bridge? If so, how?


    It can be tricky to bridge a wireless device. An alternative option is
    to use proxy arp. See http://tldp.org/HOWTO/Proxy-ARP-Subnet/why.html

    Chris

  3. Re: How do you bridge one ethernet and not the other?

    Hello,

    Chris Davies a écrit :
    >
    > It can be tricky to bridge a wireless device. An alternative option is
    > to use proxy arp. See http://tldp.org/HOWTO/Proxy-ARP-Subnet/why.html



    Unfortunately, the wireless Ethernet interface cannot be put into
    "Promiscuous" mode. This is mainly due to the lower bandwidth of the
    wireless Ethernet (2MBit/sec) meaning that we don't want to carry any
    traffic not specifically destined to another wireless Ethernet machine
    or broadcasts.


    Huh ? What does promiscuous mode have to do with the supposedly lower
    bandwidth ? Sending traffic takes bandwidth, receiving doesn't. The
    explanation found in the Linux-net wiki seems more credible to me.




    It doesn't work with my Wireless card!

    This is a known problem, and it is not caused by the bridge code. Many
    wireless cards don't allow spoofing of the source address. It is a
    firmware restriction with some chipsets. [...]

    Doing full bridging of wireless (802.11) requires supporting WDS. The
    current implementation doesn't do it.

    It is possible to do limited wireless to Ethernet functionality with
    some wireless drivers. This requires the device to be able to support a
    different sender address and source address. That is what WDS provides.


    Any opinions ?

  4. Re: How do you bridge one ethernet and not the other?

    On Jan 6, 6:05*pm, Scott Simpson wrote:
    > I have a Linux computer that sits in my living room and speaks over a
    > wireless network with WPA using wpa_supplicant. That works fine. This
    > computer also has an ethernet card in it. I'd like to connect another
    > device into that ethernet with a crossover cable and let that other
    > device use DHCP to get an address from my DHCP server (which is on the
    > other side of the wireless network). Do I set that ethernet card up as a
    > bridge? If so, how?


    O do it at home with bridge-utils and a Madwifi powered wireless
    device...

    Google it: bridge-utils

  5. Re: How do you bridge one ethernet and not the other?

    Pascal Hambourg wrote:
    > Huh ? What does promiscuous mode have to do with the supposedly lower
    > bandwidth ? Sending traffic takes bandwidth, receiving doesn't. [...]


    Two questions, two answers.

    1. You can't assign multiple MACs to a wireless interface, so the only
    other alternatives are promiscuous mode or proxy ARP.

    2. If you bridge, you bridge. Ethernet is much faster than wireless
    (obviously), so you can easily overload the wireless capability. Proxy
    ARP allows you to send only the traffic that's needed over the wireless
    connection.

    Chris

  6. Re: How do you bridge one ethernet and not the other?

    Chris Davies a écrit :
    > Pascal Hambourg wrote:
    >
    >>Huh ? What does promiscuous mode have to do with the supposedly lower
    >>bandwidth ? Sending traffic takes bandwidth, receiving doesn't. [...]

    >
    >
    > Two questions, two answers.


    Where did you see two questions ?

    > 1. You can't assign multiple MACs to a wireless interface, so the only
    > other alternatives are promiscuous mode or proxy ARP.


    I don't think you can assign multiple MAC addresses to an ethernet
    interface either, so what ? How would this help anyway ?

    > 2. If you bridge, you bridge.


    Sure. :-)

    > Ethernet is much faster than wireless (obviously),


    Not in all cases. Despite the terrible 802.11 protocol overhead which
    divides the useful throughput by 2, I believe that wireless at a
    signalling rate of 54 Mbit/s is still faster that 10Mbit/s ethernet.

    > so you can easily overload the wireless capability.


    Even though you're right, so what ? You can bridge ethernet ports at
    different speeds and overload a low speed port from a higher speed one,
    and no one complains about that. Besides, how would promiscous mode on
    the wireless interface increase the load on the wireless network ?
    Promiscuous mode is about receiving, not transmitting.

    > Proxy ARP allows you to send only the traffic that's needed over the
    > wireless connection.


    Same with most of the traffic forwarded by a bridge. A bridge doesn't
    blindly repeat all traffic, it can learn which port is connected to a
    given MAC address. Anyway neither bridging nor proxy ARP will prevent
    the wireless side from being overloaded by a faster ethernet side. And
    how do you mix proxy ARP with the DHCP requirement expressed by the OP ?

  7. Re: How do you bridge one ethernet and not the other?

    Pascal Hambourg wrote:
    > Chris Davies a écrit :
    >> Pascal Hambourg wrote:
    >>
    >>>Huh ? What does promiscuous mode have to do with the supposedly lower
    >>>bandwidth ? Sending traffic takes bandwidth, receiving doesn't. [...]

    >>
    >>
    >> Two questions, two answers.


    > Where did you see two questions ?


    Maybe I'm getting tired. Or perhaps I need new eyes. What I wrote last
    night was as clear as glass. When I re-read it again today I think
    "huh?" :-/

    I think it would be best if I bail out of this conversation. I know
    what I'm trying to say but I can't get it into words. Sorry.

    Chris

  8. Buying wifi hardware (was: How do you bridge one ethernet and not the other?)

    >> I have a Linux computer that sits in my living room and speaks over a
    >> wireless network with WPA using wpa_supplicant. That works fine. This
    >> computer also has an ethernet card in it. I'd like to connect another
    >> device into that ethernet with a crossover cable and let that other
    >> device use DHCP to get an address from my DHCP server (which is on the
    >> other side of the wireless network). Do I set that ethernet card up as a
    >> bridge? If so, how?


    > O do it at home with bridge-utils and a Madwifi powered wireless
    > device...


    Where can I find such hardware?

    I've seen sites that try to record which card uses which (set of)
    chipsets as well as data about which drivers to use for which chipset,
    but I wish someone tried to compile this info into an actual set of
    recommendations. E.g. for each type of hardware (mini-pci, PCI, USB,
    pcmcia, ...) it could start by listing the linux drivers by order of
    quality, then for each one, list the devices that are known to *always*
    use this chipset, then the devices that sometimes use it (listing which
    revisions and whether they're likely to be found in *new* hardware), ...


    Stefan

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