On 31/05/18 11:50, Raphaël Halimi wrote:
> Hi,
> 
> I have two questions about authoritative mode.
> 
> I have a home LAN, with a classic Bind / ISC DHCP / HPA TFTP setup
> (started long before dnsmasq ever existed).
> 
> Recently I decided to rent a server to externalize some public services
> (web, mail and DNS servers). This server is a libvirt/KVM hypervisor and
> all virtual machines are connected through a purely virtual bridge, and
> dnsmasq handles the DNS/DHCP/TFTP part of this LAN (the private part
> only, no relation to the the public DNS mentioned above). So I'm quite
> new to dnsmasq and so far I'm quite impressed by the vast possibilities
> it allows with such a small footprint. Note that for practical reasons,
> I don't use libvirt's builtin iptables/dnsmasq configurations, I made my
> own.
> 
> So, I interconnected both LANs through a VPN (OpenVPN) and all machines
> can happily communicate. Now I'm trying to ease the DNS administration
> part, and that's where I'm stuck on a couple of minor problems (really
> minor, since my setup works quite well, I'm just trying to perfect it a
> bit).
> 
> What I'm trying to do is to allow my home LAN's DNS system (Bind) to
> know about the remote LAN's zone, and fetch the zone data from the
> remote LAN's dnsmasq (through AXFR). It was quite easy to define a slave
> type zone, in Bind, and then allow zone transfers in dnsmasq with two
> configuration lines:
> 
> auth-sec-servers=<Bind server's IP>
> auth-peer=<Bind server's IP>
> 
> Now, the problem is that I'd like the remote LAN to be completely
> unaware (DNS-wise, at least) of the home LAN's DNS system; in other
> words, I don't want the Bind server's IP to be listed as a secondary
> server in the remote LAN's zone data. So I tried to remove the
> "auth-sec-servers=..." line, but unfortunately this prevented the zone
> transfer to work.
> 
> I know it works with Bind: I can define slave zones on some server,
> while the actual zone file on the master has no mention of any slave
> server (of course, it's still allowed in the server's configuration by
> an "allow-transfer" directive, though), making the slave server
> completely stealth. So this is my first question: is there a way to
> achieve this with dnsmasq ? If not, is this planned, or could it be
> considered for a future release ?
> 

This is just some security logic, since omiting auth-peer is allowed,
and accepts AXFR requests from anywhere, AXFR is inhibited unless
auth-sec-servers is specified. Otherwise, a dnsmasq instance without any
secondary-server configuration would be open to zone transfers from
anywhere, which is not a good default. The obvious solution is to allow
zone transfers even if there is no auth-sec-servers config, as long as
auth-peer is specified and satisfied.

This commit implements that.

http://thekelleys.org.uk/gitweb/?p=dnsmasq.git;a=commit;h=090856c7e6d483bc4d7ec41f55208a9842769c45




> My second question is more of a feature... inquiry (I was about to write
> "request" but that would be not only rude, but also not totally faithful
> to my state of mind).
> 
> As stated in dnsmasq's manual page (version 2.76, Debian stretch): "at
> present, reverse (in-addr.arpa and ip6.arpa) zones are not available in
> zone transfers, so there is no point arranging secondary servers for
> reverse lookups". So my second question is quite simple: is it planned
> for a future release ? By searching the mailing list, I saw that a lot
> of features were considered by the developer(s ?) kind of "outside of
> scope for such a tiny tool" a decade ago, yet they were finally
> implemented and are nowadays supported (the power of popular demand, I
> guess). Since the code for managing AXFR requests is already there,
> would this feature be hard to implement ?


The complexity arises because dnsmasq doesn't store "reverse" records
and PTR records in an in-addr.arpa zone. To answer individual queries,
it essentially extracts the IP address encoded in the domain name, and
looks up IP addresses in the internal data structures. This is a result
of a very old design decision.

Doing a AXFR of a in-addr.arpa zone, therefore requires iterating over
all the name<->IP address mappings, and looking for addresses that end
up in the zone in question. It would be possible, but it would be a lot
of new code, especially for IPv6.

Cheers,

Simon.

> 
> (note that as much as I'd like to, I couldn't help with this, since I'm
> a pure admin, my development skills are limited to shell and, to some
> extent, Perl).
> 
> Thanks a lot in advance for answering those two questions.
> 
> Regards,
> 
> 
> 
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