DNS

The Domain Name System is a hierarchical and decentralized naming system for computers, services, or other resources connected to the Internet or a private network.
It associates various information with domain names assigned to each of the participating entities.

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Two types of role

1 - Authoritative

Authoritative means the server is responsible for a (or several) zone(s). It is the only one (master + slaves (if exists)) which contains the records of this zone ! It's a part of the global dns database.

Example of technologies which support authoritative role by design (not by using plugin, config trick or whatever) :

2 - Recusrive

Example of technologies which support recursive role by design (not by using plugin, config trick or whatever) :

Implementation

Bind9

Bind is both an authoritative AND recursive domain main server

https://wiki.csnu.org/index.php/Installation_et_configuration_de_bind9
the process name of bind9 is "named"

rndc (bind runtime management tool)

name server control utility

Write (dump) cache of named in default file (/var/cache/bind/named_dump.db)
dumpdb [-all|-cache|-zones|-adb|-bad|-fail] [view ...]

rndc dumpdb -cache default_any

enable query logging in default location (/var/log/bind9/query.log)

rndc querylog [on|off]

toggle querylog mode

rndc querylog

flush Flushes all of the server's caches.

rndc flush

flush [view] Flushes the server's cache for a view.

rndc flush default_any

get unic master zone loaded

named-checkconf -z 2> /dev/null | grep 'zone' | sort -u | awk '{print $2}' | rev | cut --delimiter=/ -f2 | rev | sort -u
named-checkconf -z 2> /dev/null | grep 'zone' | grep -v 'bad\|errors' | sort -u | awk '{print $2}' | rev | cut --delimiter=/ -f2 | rev | sort -u

keep cache

systemctl reload bind9

empty cache

systemctl restart bind9

Knot

Troubleshooting command

Manually trigger a zone transfer from master to slave.
To run on slave side

knotc zone-retransfer example.org

Reload a zone from a disk and send NOTIFY to slave.
To run on master side

knotc zone-reload example.org

NSD

I advice you to check the fellow's tutorial

https://toutetrien.lithio.fr/article/installer-son-serveur-dns-faisant-autorite-avec-nsd

Record types

CAA

CAA stands for Certificate Authority Authorization
I.e. : Which CA do you allow to deliver certificate for your domain ?
How to generate your CAA record, for both wildcard + non-wildcard certificate common name.
https://sslmate.com/caa/

Query a dns server

dig

dig @8.8.8.8 +short +notcp  google.com 
dig @8.8.8.8 +noall +answer +tcp example.org A
dig @8.8.8.8 +noall +answer +notcp example.org A

dig @8.8.8.8 google.com +short +subnet=192.168.1.0/24
dig @8.8.8.8 google.com +short +subnet=10.0.0.0/8

dig @8.8.8.8 +short example.org +nodnssec

others options

  • +short
  • +(no)tcp
  • +(no)dnssec
  • +noall
  • +answer
  • type

Full manual

DNSSEC

  • Only one key is known and trusted by all resolver of the world. (The one of the .)
  • We have to think with zones

Each zone contains :

  • KSK : Key signing Key
  • ZSK : Zone signing Key (signed by KSK)
  • DS : (record DNS) Delegation Signer Each KSK digest of a given zone is contained in the parent zone

Si DNSSEC non activé, alors record NSEC3 ajouté (en auto souvent) dans la zone parente. (Preuve de non existence de la signature du domaine, pour ne pas faire fail le DNSSEC)

SoftHSM

softhsm : s'occupe de la gestion des clefs (stockage, generation, signature des ZSK par la KSK)

Exemple : https://dnsviz.net/d/lithio.fr/dnssec/

ods-enforcer key list --verbose --all --zone lithio.fr
Keys:
Zone:                           Keytype: State:    Date of next transition: Size: Algorithm: CKA_ID:                          Repository: KeyTag:
lithio.fr                       KSK      active    2020-04-24 05:26:19      2048  8          f88125e010c6c1ad671df83048f877f8 SoftHSM     65035
lithio.fr                       ZSK      retire    2020-04-24 05:26:19      1024  8          06ecab532b0b27c8ef2f17d6624c51d1 SoftHSM     65121
lithio.fr                       ZSK      ready     2020-04-24 05:26:19      1024  8          89087g092480f25470ce515c780ca373 SoftHSM     8685

Public Resolver classic flow

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Stub zone

A stub zone can ONLY be configured on a recursive server. This mecanism is intended to boost zone delegation, by avoiding to start again recursion process from root servers.
If you know the authoritative nameserver for a given zone you can avoid recursion process (because you already known, no need to discover).

For unbound.conf you can setup something like this :

stub-zone:
    name: "dyn.example.com"
    stub-addr: 10.10.10.10,10.10.10.11

Zone delegation

To be updated...

Performance test

DNS queryperf, un programme de mesure de performance, qui est distribué avec BIND (dans le répertoire contrib/).

Sur une Debian, queryperf peut s'installer ainsi :

Build queryperf tool

cd /tmp
apt-get source bind9
cd bind9-9.4.2/contrib/queryperf
./configure
make
# Pas de cible install dans le Makefile
sudo cp queryperf /usr/local/sbin

Nous pouvons maintenant le lancer pour voir les options (je n'ai pas tout montré) :

Usage: queryperf [-d datafile] [-s server_addr] [-p port] [-q num_queries]
                 [-b bufsize] [-t timeout] [-n] [-l limit] [-f family] [-1]
                 [-i interval] [-r arraysize] [-u unit] [-H histfile]
                 [-T qps] [-e] [-D] [-c] [-v] [-h]
  -d specifies the input data file (default: stdin)
  -s sets the server to query (default: 127.0.0.1)
  -q specifies the maximum number of queries outstanding (default: 20)
  -t specifies the timeout for query completion in seconds (default: 5)

Create your record list

In order to have an input file to give to queryperf
Form du fichier

www.0fjtvn3q0i.example     A
www.ngw7m3vq71.example     A
www.2u1.example     A

Run

./queryperf -d example.com.list -s 10.10.10.10

Sources : Stephane Bortzmeyer

Security

Web script injection via DNS

dig avalz.it TXT +short
"<script>alert(\"hi!\")</script>"

Try by yourself on weak website : https://dnslookup.online/

Root servers

https://root-servers.org/index.html

Name convention proposal

Private zone

node.fonction.env.tld

ceph case
gw1.s3.prod.example.com
gw2.s3.prod.example.com
gw.s3.prod.example.com
s3.prod.example.com CNAME gw.s3.prod.example.com

mon1.s3.prod.example.com
mon2.s3.prod.example.com
mon3.s3.prod.example.com

gw1.s3.staging.example.com
gw2.s3.staging.example.com
mon1.s3.staging.example.com
mon2.s3.staging.example.com
mon3.s3.staging.example.com

gw1.s3.dev.example.com
gw2.s3.dev.example.com
mon1.s3.dev.example.com
mon2.s3.dev.example.com
mon3.s3.dev.example.com

MinIO case
client.s3.prod.example.com
client.s3.staging.example.com
client.s3.dev.example.com

Oio case
client.s3.prod.example.com
client.s3.staging.example.com
client.s3.dev.example.com

Resources

https://www.dnsperf.com/dns-providers-list/

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