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Dear we have two dhcp server ( one running by cisco switch and another running on linux server) we use first one to get ip addresses to all clients, VOIP ...
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  1. #1
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    Two DHCP Server in same subnet


    Dear
    we have two dhcp server ( one running by cisco switch and another running on linux server)
    we use first one to get ip addresses to all clients, VOIP Phone and network printer.
    second one use to get ip addresses to only vmware player running into windows workstation to boot by pxe boot enable.
    our problem is sometimes our clients or VOIP Phone or network printer get ip address from linux server that we do not want to happen, and we want take ip address to only vmware player machines.
    please let me know how to restrict linux server to service as dhcp server for vm machines, or is there another option in cisco switch to by pass linux server can not take ip address to non vm machines.

    Regards,
    Mahdi

  2. #2
    Linux Guru Rubberman's Avatar
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    In my experience, this is not a good idea. You should only have one dhcp server per subnet. Put your virtual machines on another subnet would be my recommendation.
    Sometimes, real fast is almost as good as real time.
    Just remember, Semper Gumbi - always be flexible!

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    we use 192.168.172.* for windows workstation and another network devices except vm machines, and use 192.168.1.* to our vm machines.
    but as you know while devices dhcp enabled on network and want to take ip address, two dhcp server may be answer and one of them answer to dhcp requester.
    in this sutation problem occur and windows workstation or another network devices take ip address from linux server not cisco dhcp service enabled switch

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    Trusted Penguin Irithori's Avatar
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    Then you have two options:
    1) consolidate the config of your two dhcp servers into one. Either by keeping the two subnets or having only one.
    2) separate the two subnets via vlans.
    This is tricky as you are using vmware player. Aka: multiple vmware hosts, each of those needs to be configured the same.
    It also forbids port based vlans, you need tags.

    I would recommend 1)
    You must always face the curtain with a bow.

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    Trusted Penguin Irithori's Avatar
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    As a third option, you migtht want to consider HostOnly networking for your VMs.
    But this means, that the VMs are only reachable from their host, not network-wide.
    You must always face the curtain with a bow.

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    Linux Guru Rubberman's Avatar
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    Quote Originally Posted by Irithori View Post
    As a third option, you migtht want to consider HostOnly networking for your VMs.
    But this means, that the VMs are only reachable from their host, not network-wide.
    Good suggestion, but my advice would be to assign static IP addresses to the virtual machines - after all, it's not like they are mobile systems. In fact, our recommendation (mine, and my organization's network operations group who have to manage thousands of physical and a similar number of virtual servers) is to do just that. On our network, fixed systems (servers, non-mobile workstations) are assigned static IP addresses, and only mobile devices (laptops, phones, tablets, etc) get dhcp addresses.
    Sometimes, real fast is almost as good as real time.
    Just remember, Semper Gumbi - always be flexible!

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    Linux Guru Lazydog's Avatar
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    And that is the way it should be but many network admins are getting lazy and simple setup a DHPC server for network addressing.

    Regards
    Robert

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    Trusted Penguin Irithori's Avatar
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    This is becoming a bit OT, but dhcp != lazy.
    dhcp is a tool and it does have usecases.

    For example: dhcp is an essential part of pxe:
    With the mac address as uniq identifier (yes, only valid in a controlled network) we do realize a staged pxe environment for our server machines, with which we can
    - boot into a BurnIn ISO
    - configure a hardware raid via the vendor ISO
    - boot into the vendorīs Diagnostic ISO
    - provision an OS
    - and at the end of a machineīs lifecycle: Deconfigure the raids and wipe each of the discs
    Note, that it is decided centrally on the pxe server what happens at the next reboot. Which is *very* convenient.

    Or another usecase: Push bits like gateway, ntp, dns, etc to a whole network of workstations/laptops.
    Whenever one of these parameters changes or s/th gets added, it is much easier to add it to a central dhcp daemon than modify each client.
    You must always face the curtain with a bow.

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    Linux Guru Rubberman's Avatar
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    Irithori, I agree with you 100%. The thing is to apply the right tool to the job at hand. Getting a system stood up and running may well require dhcp, but once it is functioning, then if it is a "static" resource on the network, a static IP address is (IMO) more reasonable, and can be easily added to your local DNS server for easy access to other systems on the LAN.
    Sometimes, real fast is almost as good as real time.
    Just remember, Semper Gumbi - always be flexible!

  11. #10
    Trusted Penguin Irithori's Avatar
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    I agree you want the same IP/hostname during the lifetime of a machine.
    Which can be achieved via the fixed-address option of isc dhcpd.
    This is done with *one* source-of-truth, which generates both dns zones and dhcpd config via puppet manifests.

    So you have both: A "static" mapping of mac-ip-hostname and a really simple and uniform network config for each node via dhcp.
    You must always face the curtain with a bow.

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