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Split-Range DHCP - DNS-Servers? RRS feed

  • Frage

  • Hello,

    I'm having a Windows Server 2008 powered Network over here, where we are currently increasing redundancy everywhere.

    The current Project is the DHCP, where only one Server is powering the whole network of about 300 Clients.

    The Network ranges from 10.10.10.1 to 10.10.13.254, so should be able to cover the next years.

    Now - when introducing split-range-DHCP - I'm thinking of an (almost) 50:50 split, as this would currently allow ANY DHCP to fail, without any limitation of Service.

    Some questions: 
    I tested it with 2012 R2, it seems like Reservations are taking effect even if they are inside the "Exclusion" Range of an DHCP - right? (i.e. the second dhcp, having the exclusion range 10.10.10.10 - 10.10.11.254 can still give away the 10.10.10.19 ip, if there is a proper Reservation?)

    Now I'm thinking of "swapping" the DNS Servers to have some sort of load-balancing between the Primary and secondary DNS-Server. While this seems to work nice in My homelab, just wanted to clearify that this won't cause any headache later.

    After all, I'm thinking to deploy the following Setup:

    DHCP1:
    Range: 10.10.10.10 - 10.10.13.254
    Exclusion: 10.10.12.1 - 10.10.13.254
    Primary DNS: 10.10.10.1
    Secondary DNS: 10.10.10.2

    DHCP2:
    Range: 10.10.10.10 - 10.10.13.254
    Exclusion: 10.10.10.10 - 10.10.11.254
    Primary DNS: 10.10.10.2 (note the swap)
    Secondary DNS: 10.10.10.1 (note the swap)

    Any thoughts? Does the Swap of the DNS-Servers Show the desired "Impact" in Terms of load-balancing between the DCs?

    Dienstag, 26. Januar 2016 21:22

Alle Antworten

  • Hi, Dognose

    This is the German Technet forum, about HA. Anyway :-) we'll try to answer your questions.

    Q:

    "I tested it with 2012 R2, it seems like Reservations are taking effect even if they are inside the "Exclusion" Range of an DHCP - right? (i.e. the second dhcp, having the exclusion range 10.10.10.10 - 10.10.11.254 can still give away the 10.10.10.19 ip, if there is a proper Reservation?)"

    A:

    Normally this shouldn't happen. If DHCP1 is out of service, DHCP2 doesn't hand out addresses from DHCP1 ... I assume this has something todo, that the client only checked if it is in the same subnet as before and continued using its old IP-address.

    Q:

    "Now I'm thinking of "swapping" the DNS Servers to have some sort of load-balancing between the Primary and secondary DNS-Server. While this seems to work nice in My homelab, just wanted to clearify that this won't cause any headache later."

    A: You can do that, but normally only one DHCP is running for a long time. So this isn't the right way to load-balance DNS requests, but it will not hurt you.


    Viele Grüße, Bernd Pfann [Microsoft] - This posting is provided "AS IS" with no warranties, and confers no rights.

    Freitag, 29. Januar 2016 11:34
    Moderator
  • Hallo Bernd,

    oh, da habe ich mich im Forum vertan. Dennoch vielen Dank für deine Antwort.

    zu 1.) Beide DHCPs haben die "gleiche" Range, nur jeweils andere Exclusions. Ich hatte in meinem test-Lab den "DHCP1" für einige Tage deaktiviert - die DHCP Reservation wurde von DHCP2 vergeben, obwohl diese innerhalb der Exclusion Range lag.

    Gerade auch im TechNet gefunden, dass es so ist: http://technet.microsoft.com/en-us/library/cc737055(v=WS.10).aspx

    Reservations can be created using any IP address in the scope’s address range, even if the IP address is also within an exclusion range. Because of this design, when the 80/20 rule is implemented and some addresses in the scope are excluded (80 percent at one server, 20 percent at the other), reservations still function properly.

    zu 2.) Ja, ein aktives Load-Balancing ist das natürlich nicht. Aber geht man davon aus, dass nach Zeit "X" etwa gleich viele Clienten von DHCP1 bzw. DHCP2 versorgt sind, sollten sich die DNS Anfragen ebenfalls 50:50 aufteilen (unterstellt, dass jeder Computer gleich viel DNS Anfragen generiert, was ja auch nicht stimmt)

    Samstag, 30. Januar 2016 19:04