Ethernet bridging questions - TCP-IP

This is a discussion on Ethernet bridging questions - TCP-IP ; I'm planning on setting up ethernet bridging on a Windows XP system, in order to get a connection with OpenVPN working. From what I understand, when I bridge the two ethernet adapters in XP (*), it makes some sort of ...

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Thread: Ethernet bridging questions

  1. Ethernet bridging questions

    I'm planning on setting up ethernet bridging on a Windows XP system,
    in order to get a connection with OpenVPN working. From what I
    understand, when I bridge the two ethernet adapters in XP (*), it
    makes some sort of announcement that the bridge has been set up.

    (*) One being the physical NIC, the other the "virtual" OpenVPN NIC.

    What is the nature of this announcement? Is there an RFC that covers
    the details? Is it routable, or does it only go as far as the local
    subnets attached to the two interfaces?

    Enquiring minds want to know.

    Thanks in advance.

  2. Re: Ethernet bridging questions

    > From what I understand, when I bridge the two ethernet adapters in
    > XP, it makes some sort of announcement that the bridge has been set
    > up.


    The most obvious announcement comes in the form of STP, which XP will
    enable by default. An IP host may announce its presence in the form of a
    gratuitous ARP. Neither is routable.

  3. Re: Ethernet bridging questions

    "David Goodenough" wrote:

    > I'm planning on setting up ethernet bridging on a Windows XP system,
    > in order to get a connection with OpenVPN working. From what I
    > understand, when I bridge the two ethernet adapters in XP (*), it
    > makes some sort of announcement that the bridge has been set up.
    >
    > (*) One being the physical NIC, the other the "virtual" OpenVPN NIC.
    >
    > What is the nature of this announcement? Is there an RFC that covers
    > the details? Is it routable, or does it only go as far as the local
    > subnets attached to the two interfaces?


    If you're really bridging, and not routing, then in principle there's no
    need for any announcement. A new host connecting via an Ethernet bridged
    through the Windows machine would go about its business the usual way,
    e.g. beginning with a DHCP broadcast request, and the bridge sends on
    the broadcast to the VPN side. And the reply would come back the same
    way, because the switches between the new host and the router will have
    learned the way back.

    If the Windows machine is running STP or RSTP, then Bridge Protocol Data
    Unit (BPDU) frames are exchanged between this switch and other switches
    in the catenet, as described in IEEE 802.1D, which you can download for
    free from the IEEE web site.

    Bert


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