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Thread: Network Configuration after MAC address changed on Microsoft Hyper-V

  1. #1

    Default Network Configuration after MAC address changed on Microsoft Hyper-V

    Hello, folks

    As far as I know, Suse Linux binds the IP Configuration to the MAC Address. If MAC address is changed, it will lose connection with Network.
    So I have to remap the Network Configuration(including IP, DNS, Netmask, etc) to the new MAC address.

    However, OpenSuse doesn't have same issue such like Suse. When I did a test in OpenSuse, it didn't lose connection although MAC address changed.
    As a result, does the design that network configuration binds to the MAC address be changed in OpenSuse?

    Best Regards,
    Haewon

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    Default Re: Network Configuration after MAC address changed on Microsoft Hyper-V

    Hello and welcome here.

    Can you please first and foremost always tell what version of openSUSE you use when you start a thread about a problem/question?

    When you have a problem with SUSE LInux Enterprise (again without version given), you are at the wrong forum. Most peopel here realy do not kno much about it, let alone about the subtle differences.
    Henk van Velden

  3. #3

    Default Re: Network Configuration after MAC address changed on Microsoft Hyper-V

    Thank you for reply
    I'm sorry I didn't write what you need.
    OpenSuse Version 3.11.6-4-desktop

    Is OpenSuse be designed not to bind network configuration(IP Address, NetMask, etc) to MAC Address?
    In other Linux distribution, because network configuration is bound to MAC address, it will lose its network connection after MAC address changed.
    Any ideas would be very appreciated.

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    Default Re: Network Configuration after MAC address changed on Microsoft Hyper-V

    Quote Originally Posted by hwjung View Post
    Thank you for reply
    I'm sorry I didn't write what you need.
    OpenSuse Version 3.11.6-4-desktop
    Sorry, but that is not the openSUSE version. (Most likely you're referring to the kernel version.)
    Code:
    cat /etc/os-release

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    Default Re: Network Configuration after MAC address changed on Microsoft Hyper-V

    Quote Originally Posted by hwjung View Post
    Is OpenSuse be designed not to bind network configuration(IP Address, NetMask, etc) to MAC Address?
    As far as I know, opensuse is no different from other distros in this respect.

    You are actually confusing multiple issues.

    If you acquire an IP address using DHCP, then the DHCP server bases that on MAC address. If you change the MAC address, then the DHCP server will assign a different IP address.

    If you statically assign the IP, then it is assigned to the device. If you change the MAC address on the device, you will still use the same IP address.

    Communication with other computers on your LAN is always done with the use of MAC address. The "arp" cache provides a short-term mapping between IP and MAC. If you change the MAC address, then other systems on your LAN will lose contact. They will continue to send packets to the old MAC. But, after a timeout, they should discover the new MAC and resume communication.

    Presumably there is a router on your LAN to connect to the rest of the Internet. If a change in MAC causes a temporary communication failure with the router, that will affect connects to the Internet.
    openSUSE Leap 15.3; KDE Plasma 5.18.6;

  6. #6

    Default Re: Network Configuration after MAC address changed on MicrosoftHyper-V

    On 05/29/2014 08:56 AM, nrickert pecked at the keyboard and wrote:
    > hwjung;2646089 Wrote:
    >> Is OpenSuse be designed not to bind network configuration(IP Address,
    >> NetMask, etc) to MAC Address?

    > As far as I know, opensuse is no different from other distros in this
    > respect.
    >
    > You are actually confusing multiple issues.
    >
    > If you acquire an IP address using DHCP, then the DHCP server bases that
    > on MAC address. If you change the MAC address, then the DHCP server
    > will assign a different IP address.
    >
    > If you statically assign the IP, then it is assigned to the device. If
    > you change the MAC address on the device, you will still use the same IP
    > address.
    >

    No it will not as the static address is assigned to the old mac address.
    The new mac address will get a different address via DHCP until the new
    mac address is assigned the original static address.

    Ken

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    Default Re: Network Configuration after MAC address changed on MicrosoftHyper-V

    Quote Originally Posted by kensch View Post
    No it will not as the static address is assigned to the old mac address.
    The new mac address will get a different address via DHCP until the new
    mac address is assigned the original static address.

    Ken
    That just adds confusion.

    The traditional meaning of "statically assigned", particularly when contrasted with "DHCP", is that the IP address is assigned with the "ifconfig" command, or with "ifup" settings. The IP address is assigned to the device.

    Yes, you can have a static entry in the DHCP tables on the DHCP server. But that's covered in my earlier comment on using DHCP to acquire IP address.
    openSUSE Leap 15.3; KDE Plasma 5.18.6;

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    Default Re: Network Configuration after MAC address changed on MicrosoftHyper-V

    Quote Originally Posted by nrickert View Post
    That just adds confusion.

    The traditional meaning of "statically assigned", particularly when contrasted with "DHCP", is that the IP address is assigned with the "ifconfig" command, or with "ifup" settings. The IP address is assigned to the device.

    Yes, you can have a static entry in the DHCP tables on the DHCP server. But that's covered in my earlier comment on using DHCP to acquire IP address.
    I agree with you. A static IP address is called as such from the systems view and means that it is not configured using DHCP And being connected to the device (earlier something like eth0,now newer naming) through ifup, and not to the MAC address. Thus when the MAC address chances (even when the NIC is replaced, but again becomes eth0), it will get the same IP address on boot (or other ifup of the NIC)

    When you have the DHCP server configured in a way that it serves allways the same IP address to the same MAC address, then that is not called a static IP address from the system's point of view (if at all).
    Henk van Velden

  9. #9

    Default Re: Network Configuration after MAC address changed on MicrosoftHyper-V

    On 05/29/2014 10:36 AM, hcvv pecked at the keyboard and wrote:
    > nrickert;2646171 Wrote:
    >> That just adds confusion.
    >>
    >> The traditional meaning of "statically assigned", particularly when
    >> contrasted with "DHCP", is that the IP address is assigned with the
    >> "ifconfig" command, or with "ifup" settings. The IP address is assigned
    >> to the device.
    >>
    >> Yes, you can have a static entry in the DHCP tables on the DHCP server.
    >> But that's covered in my earlier comment on using DHCP to acquire IP
    >> address.

    > I agree with you. A static IP address is called as such from the systems
    > view and means that it is not configured using DHCP And being connected
    > to the device (earlier something like eth0,now newer naming) through
    > ifup, and not to the MAC address. Thus when the MAC address chances
    > (even when the NIC is replaced, but again becomes eth0), it will get
    > the same IP address on boot (or other ifup of the NIC)
    >
    > When you have the DHCP server configured in a way that it serves allways
    > the same IP address to the same MAC address, then that is not called a
    > static IP address from the system's point of view (if at all).
    >
    >

    Then you are NOT using DHCP to serve an address to the machine but
    assigning one statically on the machine.

    Ken

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    Default Re: Network Configuration after MAC address changed on Microsoft Hyper-V

    To the OP:
    Obviously your incorrect use of terminology is causing confusion, here are some common definitions:

    DHCP (automatically assigned addresses) - When a machine (virtual or physical) boots up on the network, it broadcasts its existence and a DHCP server responds by providing a unique network configuration the machine can use. You configure the client machine as a "DHCP client," on openSUSE typically in YAST or Network Manager.

    Static Address - When a machine (virtual or physical) boots up on the network, it is pre-configured with known network settings. On openSUSE this is more commonly configured using YAST, but can also be configured in Network Manager.

    Reserved Lease - This is a hybrid of the above, when a machine (virtual or physical) boots up on the network, it broadcasts its existence and a DHCP server responds by first finding the machine's MAC address in a list of reserved addresses mapped to specific IP addresses. In this way, the newly booted machine is always assigned the same IP address whereas a normal DHCP address could change.

    Solutions to the above:

    First, you should understand that the MAC address is always the fundamental way a machine identifies itself but it is difficult to use when designing an IP network. For that reason although machines communicate fundamentally using MAC addresses, they normally find and manage each other using IP addresses which are mapped locally to the MAC address. In this way there is typically a "soft relationship" (configurable) between the IP address and the MAC address.

    Note that the following only re-establishes fundamental networking. If you're also running network security, ie LDAP, AD, etc. then there will be other far-ranging consequences. That gets complicated, would be something you need to contact your Network Administrator about (and would more than triple the length of this post).

    DHCP - Since the DHCP server assigns "some" IP address to any machine that needs one, all you need to do is restart your client machine's networking service which can be done by the following command, note that this is comparable to the Windows "ipconfig -renew"
    Code:
    systemctl restart network
    When the local machine's network service restarts, it again broadcasts requesting an IP address. The DHCP server responds, replacing any old configuration on the machine.

    Static IP address - Depending on circumstances, changing your MAC address shouldn't cause much of a network issue although you may need to either wait or manually initiate some ARPs to announce your machine's changes.

    Reserved Lease - Since the DHCP server maintains a list of MAC addresses mapped to IP addresses, that list would have to be modified, followed by the procedure described for a regular DHCP IP address above.

    Lastly, these are fundamental principles that apply to any virtualized or physical Hosts, it does not matter that your Guest is running on Hyper-V.

    HTH,
    TSU

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