[Tfug] Problems with local DNS using DD-WRT and dnsmasq

[John Gruenenfelder]

TFUG,

Hello again.  I'm having some annoying problems with my current installation
of DD-WRT when trying to set up local DNS resolution.  So far, I've asked
first in the DD-WRT forum with no reply and then posted on StackExchange
(superuser forum) again with no reply.  I hope somebody here is knowledgeable
about DD-WRT and dnsmasq in particular.

I can work around the problem on most of my machines by putting the correct
entries in the /etc/hosts file, but that's not really an option for other
machines like Android phones.  The other big issue is portability (physical,
that is).  When an Android phone or a laptop is connected through the LAN, it
needs to resolve the hostnames to internal IP addresses, but when it is
connecting from the Internet (to the one host accessible that way) the same
hostname needs to resolve to the external IP.  You can do this with local DNS
resolution but not so much with static /etc/hosts entries.

Anyway, here is my original forum posting with all the config info.  I really
hope somebody here has some ideas because, so far, the Internet has been a big
let down on this issue...  :(   Thanks!

----------------------------------------

I just upgraded my ASUS RT-AC56U router to a newer DD-WRT, build 23940. This
is the latest as provided by the website's router database even though it is
from April 22, 2014. If a newer release contains a fix for the following DNS
issues, I would install it, but I don't want to make that jump unless I know
for sure that I need a newer build (that is, I'm trying to avoid beta
builds).

My configuration is simple enough, but I am having trouble getting my full DNS
configuration working. My network setup:

    Using subnet 192.168.1.0
    Router at 192.168.1.1
    Two machines with static IPs: 192.168.1.2 and .3
    One static DHCP lease at: 192.168.1.5
    All other wired and wifi clients are DHCP

Using just the settings available in the admin GUI, with most everything set
at the defaults, I get no local DNS resolution at all. DNS for the wider
Internet does work. After searching around the Net and on both Stack Exchange
and DD-WRT forums, I did find some helpful config advice. I have the following
in the "Additional DNSMasq Options" box:

    #####
    # Additional dnsmasq config options
    #####

    local=/merseine.nu/
    expand-hosts
    domain-needed

    ### DNS records - merseine.nu home network ###
    #host-record=moongate.merseine.nu,moongate,192.168.1.1
    #host-record=swordfish.merseine.nu,swordfish,192.168.1.2
    #host-record=bebop.merseine.nu,bebop,192.168.1.3

    ### DNS records (reverse lookup) - merseine.nu home network ###
    ptr-record=1.1.168.192.in-addr.arpa,moongate.merseine.nu
    ptr-record=2.1.168.192.in-addr.arpa,swordfish.merseine.nu
    ptr-record=3.1.168.192.in-addr.arpa,bebop.merseine.nu

    ### static DHCP records ###
    dhcp-host=e8:03:9a:38:e4:90,192.168.1.5,redtail.merseine.nu,infinite

With this setup, remote DNS functions, but I can do local resolution only on
the "redtail" hostname. Notice that the host-record lines are commented
out. If I uncomment them, DNSMasq no longer starts on the router and therefore
all DNS is broken.

If it helps, the remaining DNS/DNSMasq related settings in the GUI are:

    Basic setup -> DHCP settings:

    Use DNSMasq for DHCP: checked
    Use DNSMasq for DNS: checked
    DHCP-Authoritative: checked


    Services -> DHCP server:

    Used domain: LAN & WLAN
    LAN domain: merseine.nu


    Services -> DNSMasq:

    DNSMasq: cheked
    Local DNS: checked
    No DNS rebind: checked

What am I doing wrong here? Is 'dhcp-host' the wrong option to use? From the
manual, it should add A, AAAA, and PTR records, and I think that is what I
want it to do. I believe the manual also said that 'host-record' lines would
also create all of the necessary records, but, as stated above, using them
appears to create an invalid configuration which then prevents dnsmasq from
even starting.

It seems like much of this would be simpler if I could just add these items to
/etc/hosts on the router, but you cannot do that from the admin GUI, and I
think if I edit that file on the router it will be overwritten (probably on a
reboot).

Everything else that I use dd-wrt for is functioning properly. I don't make
much use of many of the more advanced features, so most of them are disabled.


-- 
--John Gruenenfelder    Systems Manager, MKS Imaging Technology, LLC.
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