Re: keeping sites off

From: Jonathan de Boyne Pollard <J.deBoynePollard-newsgroups_at_NTLWorld.COM>
Date: Mon, 30 Mar 2020 09:38:36 +0100

Laurent Bercot:

> What I do is:
> *
> run a tinydns on another IP address (if you only have 1 nic, you
> can still attribute several IPs to it)
> *
> fill that tinydns with sink data for the things I want to block
> *
> configure my dnscache to query my internal DNS server for the
> zones I want to block. In your case, if you tell your dnscache
> that your internal DNS server is authoritative for the
> zone, any query for will go to
> your internal server.
> *
> no /etc/hosts manipulation needed.

This is the third-best way to achieve this. The second-best way is a
variant. In the third-best way there's still a lot of setup and
on-going maintenance involved in the servers/ directory of the dnscache
service, as one adds/removes domain names. In the second-best way,
tinydns also serves up the root of the DNS namespace, delegating to the
next level of servers in the same way that the public root content DNS
servers do, and dnscache is simply configured to start with that root
content server. There's no further on-going dnscache work in this
approach, just the maintenance of the entries in the tinydns database.

A side-benefit is that this also makes your traffic to the root content
DNS server entirely private and not susceptible to network outages.
Whilst it applies less to real existing domain names, this in particular
helps with some of the other stuff that tends to leak out in DNS lookups
(caused by a whole bunch of things from the DNS client library search
path, through non-existent top-level domains, to applications passing
human-form IP addresses to DNS lookup), which would otherwise end up as
negative responses from the public root content DNS servers. Moreover,
properly dnscache should always be providing split-horizon DNS service
for address-to-name lookups of all of your RFC 1918 IP addresses, and
name-to-address lookups of any internal subdomains for your LAN(s),
which are both more private stuff that the outside world should never
see. This also can achieve that, as a further side-benefit, simply with
further additions to the tinydns database, and without need to configure
split-horizon in dnscache.

In the service bundles that accompany the nosh toolset, I supply a
tinydns_at_127.53.0.1 service bundle that does all of these. Its Makefile
populates its database with RFC 1918 IP address stuff, the root data
pulled from ICANN, and administrator-controlled extra stuff (where the
re-pointed wildcard domain name data would go).


The best way, however, is to realize that using the DNS for this breaks
every non-HTTP(S) protocol, and do this for HTTP(S) only. I've myself
done this in two ways in the past: with a custom proxy.pac/wpad.dat file
that the WWW browsers load, redirecting all of the relevant domains in
ECMAScript in the WWW browser itself; and with a fully-fledged proxy
HTTP server that I wrote, that used a database of URL patterns (not just
domain names) and how they should be handled in HTTP, including (as one
of several possibilities) rewriting them into temporary redirects to a
small static content HTTP server that served up coloured rectangles as
placeholder images amongst other things. These are the basic approaches
of most non-toy WWW advert-blockers, you will find.
Received on Mon Mar 30 2020 - 08:38:36 UTC

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