Split DNS inconsistencies

johnpoz

I checked his authoritative nameservers for that domain on the public net, and they only respond with 1 record for that uk host.

If nslookup or dig or host resolves the public, but ping resolves some rfc1918 address I assume he is not asking dns but finding it in a hosts file on the pfsense box. Pfsense stores the overrides in the hosts file, and it also can store dhcp leases in the hosts file.

So even if he has no host override on his forwarder to point to the local rfc1918 address, if he gave the box a dhcp IP then its quite possible its in his /etc/hosts file and there is where applications like ping could find it since they look there before asking dns.

bryan.paradis

@johnpoz:

I checked his authoritative nameservers for that domain on the public net, and they only respond with 1 record for that uk host.

If nslookup or dig or host resolves the public, but ping resolves some rfc1918 address I assume he is not asking dns but finding it in a hosts file on the pfsense box. Pfsense stores the overrides in the hosts file, and it also can store dhcp leases in the hosts file.

So even if he has no host override on his forwarder to point to the local rfc1918 address, if he gave the box a dhcp IP then its quite possible its in his /etc/hosts file and there is where applications like ping could find it since they look there before asking dns.

I see.

 Do not use the DNS Forwarder as a DNS server for the firewall	
By default localhost (127.0.0.1) will be used as the first DNS server where the DNS forwarder is enabled, so system can use the DNS forwarder to perform lookups. Checking this box omits localhost from the list of DNS servers.

With this on I do not get queries from pfsense shell shown in the resolver log either. Guess that makes sense then :'(

@zandr:

Yes, on the pfsense box itself.

I've fixed the customer box by switching to unbound, let me see if I can reproduce this on my own machine.

Here we go:

[2.1-RELEASE][amilewski@ashby.milewski.org]/home/amilewski(2): host uk.milewski.org
uk.milewski.org has address 5.2.16.118
[2.1-RELEASE][amilewski@ashby.milewski.org]/home/amilewski(3): ping uk.milewski.org
PING uk.milewski.org (172.23.16.11): 56 data bytes
64 bytes from 172.23.16.11: icmp_seq=0 ttl=64 time=1.130 ms

[EDIT: I do not see queries for this host at all in /var/log/resolver.log. Should I be looking somewhere else?]

What are all the steps you are doing the reproduce this without the rinetd and vhosts package?

zandr

Sorry, distracted by other things, working around the fact that I can't develop packages because the xmlrpc server repository has been taken off the net. >:(

Anyway… to reproduce this problem, add a host override for some external host (in above case, uk.milewski.org) pointing to an address on the LAN (above, 172.23.16.11) and check "Do not use the DNS Forwarder as a DNS server for the firewall".

But as you've pointed out, since overrides are stored in /etc/hosts, the firewall still sees overrides even if the firewall is not using the forwarder. This seems broken, as it means the "Do not use..." checkbox doesn't do a lot.

I'm guessing at this point, but it looks like it's dnsmasq that's copying the overrides into /etc/hosts, and that unbound reads the xml without messing with /etc/hosts.

bryan.paradis

@zandr:

Sorry, distracted by other things, working around the fact that I can't develop packages because the xmlrpc server repository has been taken off the net. >:(

Anyway… to reproduce this problem, add a host override for some external host (in above case, uk.milewski.org) pointing to an address on the LAN (above, 172.23.16.11) and check "Do not use the DNS Forwarder as a DNS server for the firewall".

But as you've pointed out, since overrides are stored in /etc/hosts, the firewall still sees overrides even if the firewall is not using the forwarder. This seems broken, as it means the "Do not use..." checkbox doesn't do a lot.

I'm guessing at this point, but it looks like it's dnsmasq that's copying the overrides into /etc/hosts, and that unbound reads the xml without messing with /etc/hosts.

I looked through all the code and after the dnsmasq manual. Below is what I have come up with to clarify:

The Option "Do not use the DNS Forwarder as a DNS server for the firewall" removes 127.0.0.1 from firewall's resolv.conf only.
If you want DNS forwarder to not be used for dhcp clients you need to specify DNS servers in Services -> DHCP Server or Services -> DNS Forwarder -> Uncheck Enable
"Host Overrides" are host file based overrides and it is done through php code only. Dnsmasq will read from this file for lookups though.
If you want a record and not a host override you need to use "host-record=www.fudzilla.com,192.168.55.1" and you will see the expected result.
The overrides you are using in unbound are much like these ones. Where as pFsense is using host based overrides on that page that dnsmasq can read for lookups unforunately this will affect other things on the firewall side.

Hope that helps.

–host-record=<name>[,<name>….][<ipv4-address>],[<ipv6-address>]
Add A, AAAA and PTR records to the DNS. This adds one or more names to the DNS with associated IPv4 (A) and IPv6 (AAAA) records. A name may appear in more than one host-record and therefore be assigned more than one address. Only the first address creates a PTR record linking the address to the name. This is the same rule as is used reading hosts-files. host-record options are considered to be read before host-files, so a name appearing there inhibits PTR-record creation if it appears in hosts-file also. Unlike hosts-files, names are not expanded, even when expand-hosts is in effect. Short and long names may appear in the same host-record, eg. –host-record=laptop,laptop.thekelleys.org,192.168.0.1,1234::100</ipv6-address></ipv4-address></name></name>

johnpoz

I am curious why this is an issue to be honest? If your creating records that point to local an address "172.23.16.11"

Why would you not want to use this? If your not using it, why create it in the first place?

zandr

@johnpoz:

Why would you not want to use this? If your not using it, why create it in the first place?

There are lots of reasons why you'd want to run split DNS. In my case, I need to run rinetd on the firewall in front of a real host on the internet. My LAN clients need to resolve a certain hostname to a Virtual IP on the firewall, but I need rinetd to be able to resolve the real external address of that hostname so it can connect.

johnpoz

I understand the reason for split dns, that is not what I asked.. My question is to why you want pfsense to resolve the public record vs the local private record? But now I see your running an application on pfsense that you don't want to use the host file to resolve.

But why does pfsense or apps on it have to resolve anything? Why don't you just forward to the IP your wanting rinetd to forward too vs using fqdn? Does this fqdn change its IP?

zandr

@johnpoz:

But why does pfsense or apps on it have to resolve anything? Why don't you just forward to the IP your wanting rinetd to forward too vs using fqdn? Does this fqdn change its IP?

Circling back to this, I certainly could use a hard-coded IP. That would mean that if the service I'm using moves, we have to remember to reconfigure the pfsense box as well. This is exactly what DNS was designed to avoid.

Unbound doesn't seem very stable, so if there's a way to get this to work, perhaps by having dnsmasq use a separate file rather than /etc/hosts, that would be a win for me.

johnpoz

@zandr:

perhaps by having dnsmasq use a separate file rather than /etc/hosts, that would be a win for me.

Well just use

"host-record=www.fudzilla.com,192.168.55.1"

See the post from above.

So here is my /etc/host

[2.1.1-PRERELEASE][admin@pfsense.local.lan]/root(2): cat /etc/hosts
127.0.0.1 localhost localhost.local.lan
192.168.1.253 pfsense.local.lan pfsense
192.168.1.31 raspberrypi.local.lan raspberrypi
192.168.1.99 popcorn.local.lan popcorn
192.168.1.100 i5-w7.local.lan i5-w7

snipped

dhcpleases automatically entered

192.168.1.215 w81.local.lan w81 # dynamic entry from dhcpd.leases
192.168.1.214 2012r2.local.lan 2012r2 # dynamic entry from dhcpd.leases
192.168.2.217 G500.local.lan G500 # dynamic entry from dhcpd.leases
192.168.2.213 android-497a3c8329e0a007.local.lan android-497a3c8329e0a007 # dynamic entry from dhcpd.leases
192.168.2.211 Chromecast.local.lan Chromecast # dynamic entry from dhcpd.leases
192.168.3.100 W7X64-VM.local.lan W7X64-VM # dynamic entry from dhcpd.leases

etc…

There is no www.fudzilla.com in there.. But if I put in the above, see attached -- so pfsense using outside dns, not itself resolves the public IP for that host, but boxes on my lan using pfsense for dns resolve the record I put in. So as long as you don't have it entered via dhcp record your fine.

dnsmasgrecord.png_thumb

zandr

host-record is exactly what I was after. I missed that the first time I read bryan.paradis's post, thanks johnpoz for pointing it out again.

This is great, it lets me ditch unbound (which hasn't been the most stable in production)

Thanks again,
-Zandr