Dhcpd does not hand out default DNS server when using a tagged interface

  • Hi,

    noticed the following symptom:

    After changing to an all-tagged L2 environment in one off my setups, I noticed that DHCP server did not hand out a DNS server to the dhcp clients.
    "leave blank" -> no dns server handed out with the options. This happens only when I assign a tagged vlan to my "LAN". Untagged the issue does not show. It is repeatable.

    Easily solved by setting the DNS server's (pfSense in this case) IP in "Services\DHCP Server\LAN\Servers\DNS Servers", but smells like a bug.
    My system = Version 2.3.2-RELEASE (amd64) , built on Tue Jul 19 12:44:43 CDT 2016 , FreeBSD 10.3-RELEASE-p5.

  • Rebel Alliance Developer Netgate

    DHCP does not and cannot see any difference between a tagged and untagged interface. Something else in your configuration must be different between those interfaces.

    pfSense will hand itself out as a DNS server if the DNS resolver or DNS forwarder is enabled. If neither are enabled, it hands out the servers from System > General. Otherwise you have to set the DNS servers on the DHCP settings manually.

  • Hmm, tnx for the feedback, and agreed that makes sense, but I have gone back and forward a couple of times on this just to rule out human error (me ;)) and there isn't much exotic in my setup (imho).
    I'm using the DNS forwarder btw.
    I was -still am- in the impression the dhcpd just didn't hand out dns information. I'll try to repeat the test (but this time with packet capture on 67&68) when I get the chance during the next couple days and report back.

  • LAYER 8 Global Moderator

    so your saying these clients on your vlan get dhcp its just missing dns??

    I can tell you that my dhcp settings for a vlan is left blank and it hands out the Pfsense IP in that vlan as the dns server as it is designed to do..

    if it didn't then none of my wifi clients that are on vlans via tags would work..

    Here as you can see I have a vlan 500, this is via wifi AP where that ssid has a vlan tag on it.  So pfsense has that vlan setup, its dhcp has no dns set all blank both on the general pool and the specific reservation I created for that client.  I then force a reconnect of that client so it would send a dhcp request that I did a packet capture of.  As you can clearly see it sent out the dns with is pfsense IP address in that vlan.

    I don't know what could be causing or what your perceiving as a problem, but I can assure you pfsense hands out its IP for vlan interfaces for dns just fine.

  • Yes I did make that statement, as it was the observed behavior.
    Though in my case, it was not an OPT interface, it was on LAN (unsure that would make any difference). I have other setups, where I have many vlans on the same IF and as you say that works fine.
    However, I was setting my WAN and LAN as tagged on the same IF (different tags off course ;)), and from the moment I changed LAN as a tagged IF I did get an IP but no DNS server etc. Therefor I made this topic.
    The more I think on it the more I have the idea I must have done something odd…
    Anyway, allow me to test again (this weekend) & report back before wasting too much bandwidth on this (while it's unconfirmed).

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