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A gateway can not be assigned to DNS server which is on a directly connected network

Scheduled Pinned Locked Moved DHCP and DNS
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  • G
    geminux
    last edited by Feb 18, 2021, 2:21 PM

    Hello,

    I'm facing an issue while configuring a DNS forwarder.
    In my configuration, the upstream DNS server is also the upstream gateway.

    Let's say that :

    • LAN is 192.168.0.0/24
    • WAN is 192.168.255.0/24. (private network is not a mistake, this is an interconnection to the upstream router). .253 is pfsense, .254 is the upstream router.
    • An upstream gateway is declared on WAN interface with 192.168.255.254
    • The upstream router also privide the DNS service (And I have to use it for this WAN interface.
      It is related to MPTCP bypass function on the upstream router. No choice)
    • (of course nat is disabled on pfsense)

    So in "general config" I try to add 192.168.255.254 as DNS forwarder, and make it use the gateway (which has the same IP)

    It gives the following error :

    A gateway can not be assigned to DNS '192.168.255.254' server which is on a directly connected network.
    

    I can't figure out if it's a feature or a bug. What would be the point of such limitation ?

    Please note that everything is working well if I use an online DNS like 1.1.1.1 or 8.8.8.8 except that I will have some MPTCP limitation if I can't use 192.168.255.254 instead.
    I'm using version 2.4.5-RELEASE-p1.

    Does anybody have an explanation (or a solution) ?

    Thanks

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    • G
      geminux
      last edited by Feb 18, 2021, 3:35 PM

      OK I'm dumb... 🤦 🤦

      It's obvious that this gateway will be used to reach 192.168.255.254 DNS since it is a direct attached subnet... There is no risk that it uses any other gateway...

      I sticked too hard to the rule "at least one DNS must be set per gateway in a multiwan environment" In the case of a DNS in a WAN subnet, selecting none is fine because routing through this interface is implicit.

      My use case is not the most widespread but maybe a clarification could be made in the documentation. Meanwhile answer can now be found here 😊

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