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Resolver Lab

The Resolver Lab is a comprehensive platform that offers a controlled testing environment where various DNS resolver implementations can be thoroughly assessed and compared. At its core, the lab features dockerized resolver containers for testing with variables for changing versions and configurations. The Resolver Lab includes an authoritative name server for a pseudo-top-level domain (.lab), a suite of authoritative second-level domain name servers, and a versatile client script for structured query testing. These components collectively facilitate the analysis of resolver behavior under various scenarios in an isolated environment entirely under the user's control. Interacting with the resolvers and observing queries at the authoritative name servers reveal valuable insights into resolver behavior and potential vulnerabilities.

Components

Docker compose file

The docker-compose.yml specifies a network and 9 services: 4 test resolvers, 1 auxilliary resolver, 1 authoritative TLD name server, and 3 authoritative SLD name servers. The services specify images built beforehand. The 4 test resolvers have their version and configuration file parameterized, set in a separate .env file.

Resolver containers

The heart of the Resolver Lab is its collection of Dockerfiles, each tailored to build a distinct open-source DNS resolver:

  • Unbound (/unbound) [10.0.53.1]
  • Bind (/bind) [10.0.53.2]
  • Knot (/knot) [10.0.53.3]
  • PowerDNS (/powerdns) [10.0.53.4]

There are build.sh scripts taking the version of the software as a parameter:

cd unbound
./build.sh 1.17.1

By containerizing these resolvers, you can easily spin up stable instances for testing. Each test resolver has a "configs" directory, containing configuration files which can be set in run-time using the .env file.

Authoritative name server containers

The lab includes an authoritative TLD name server configured for the pseudo-top-level .lab zone. This name server facilitates testing scenarios by responding to queries for domains under the .lab zone. Each of the four resolvers have been configured to use this local authoritative TLD name server when resolving a .lab domain. This is particularly useful for observing resolver behavior when interacting with authoritative sources. To comprehensively analyze the behavior of recursive resolvers, the Resolver Lab incorporates various authoritative SLD name servers in the .lab zone:

  • fpdns.lab (/fpdns.lab)
  • oldqmin.lab (/qmin.lab)
  • newqmin.lab (/qmin.lab)
  • polar.lab (/polar.lab)

These authoritative name servers are designed to interact with the resolvers and log queries for analysis. This data serves as a valuable resource for assessing resolver behaviour and potential vulnerabilities.

Client scripts

The client scripts bundled with the lab allows structured queries to be sent to a defined list of resolvers. The lab currently have the following scripts:

  • one-to-many.py, takes a domain name and a list of resolvers

How to run

Make sure that you have docker/-compose and dig or equivalent installed.

docker compose up -d
dig @10.0.53.1 www.example.com +short
dig @10.0.53.1 a.b.newqmin.lab TXT +short
docker compose down

You can also run the following to use host names in /etc/hosts:

sudo sh -c 'cat hosts >> /etc/hosts'
docker compose up -d
dig @unbound.resolver www.example.com +short
dig @powerdns.resolver www.example.com +short
dig @bind.resolver www.example.com +short
dig @knot.resolver www.example.com +short
docker compose down

Testing with different versions

The Resolver Lab offers the flexibility to test different versions and configurations of the resolvers. By building new images ([resolver]/build.sh [version]) and modifying the contents of the environment file (.env), you can build the resolver container to run specific versions. Adding configuration files ([resolver]/configs/new.conf) and selecting them in the environment file allows changing of resolver configurations without rebuilding the image.

.env

UNBOUND_VER=1.17.1
UNBOUND_CONF=qmin-off

BIND_VER=9.18.15
BIND_CONF=qmin-relaxed

KNOT_VER=5.6.0
KNOT_CONF=default

POWERDNS_VER=4.8.4
POWERDNS_CONF=forward

When building new images, these are some nice debugging tools to include:

  • vim
  • net-tools
  • tmux
  • dnsutils
  • iproute2