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dns.md

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+# DNS - Domain Name System
+
+Resolves hostnames and fully qualified domain names (FQDNs) to IP addresses.
+
+| TCP / UDP | Port | Description                                                            |
+| --------- | ---- |------------------------------------------------------------------------|
+| UDP       | 53   | - DNS client requests<br/>- DNS server replies                         |
+| TCP       | 53   | - Dynamic DNS<br/>- Zone transfers between DNS servers for replication |
+
+### DNS Server Software
+
+- [ISC Bind](https://www.isc.org/bind/) - the classic unix DNS - still runs most of the internet
+- [DjbDNS / TinyDNS](https://cr.yp.to/djbdns.html) - smaller faster DNS server
+- [DNSmasq](https://thekelleys.org.uk/dnsmasq/doc.html) - simple, serves `/etc/hosts` as DNS records
+  - good for local labs or small local networks
+- [InfoBlox](https://www.infoblox.com/) - enterprise DDI (DNS, DHCP, IPAM - IP Address Management) and threat protection - see [infoblox.md](infoblox.md)
+
+#### Lab DNS - Create FQDNs with embedded IP addresses
+
+https://sslip.io/ - maps anything `<anything>[.-]<IP Address>.sslip.io` in either 'dot' or 'dash' notation to the embedded IP address.
+
+https://nip.io - maps `<anything>[.-]<IP Address>.nip.io` in either 'dot' or 'dash' notation to the embedded IP address.
+
+Commonly used for labs and demos where you need to put hostnames / FQDNs in software configuration instead of IP addresses.
+
+
+### Public DNS Servers for Clients
+
+Public DNS servers available for clients to use:
+
+- `1.1.1.1` - Cloudflare - privacy first DNS
+- `8.8.8.8` - Google DNS servers (as if they don't track you enough)
+- `8.8.4.4` - Google DNS servers
+- `208.67.222.222` - OpenDNS
+- `208.67.220.220` - OpenDNS
+
+### Misc
+
+TSIG key - shared key for one-way hash auth for DDNS and zone transfers
+
+DNS Security - see [security.md](security.md)
+
+### Linux Packages for DNS Clients
+
+Contains the `host` and `dig` commands:
+
+```shell
+sudo yum install -y bind-utils
+```
+
+### DNSmasq on macOS
+
+```shell
+brew install dnsmasq
+```
+
+To configure dnsmasq, copy the example configuration to `/usr/local/etc/dnsmasq.conf`
+and edit.
+
+```shell
+cp /usr/local/opt/dnsmasq/dnsmasq.conf.example /usr/local/etc/dnsmasq.conf
+```
+
+```shell
+vim /usr/local/etc/dnsmasq.conf
+```
+
+Sample config I used to use in labs to only serve local VirtualBox VMs -
+only listens on `vboxnet0` interface and contains `*.local` lookups:
+
+```
+local=/dev/
+local=/local/
+local=/localdomain/
+local=//
+interface=vboxnet0
+bind-interfaces
+```
+
+To have launchd start dnsmasq at startup:
+
+```shell
+sudo cp -fv /usr/local/opt/dnsmasq/*.plist /Library/LaunchDaemons
+```
+
+Then to load dnsmasq now:
+
+```shell
+sudo launchctl load /Library/LaunchDaemons/homebrew.mxcl.dnsmasq.plist
+```
+
+
+
+
+### DNSMasq on RHEL7
+
+```shell
+sudo yum install -y dnsmasq
+```
+
+```shell
+dnsmasq --test
+```
+
+```shell
+sudo systemctl enable dnsmasq
+```
+
+```shell
+sudo systemctl start dnsmasq
+```
+
+Test DHCP response:
+
+```shell
+sudo yum install -y dhcping
+```
+
+```shell
+sudo dhcping -s localhost
+```
+
+### DDNS - Dynamic DNS
+
+Requires TCP port 53
+
+http://www.semicomplete.com/articles/dynamic-dns-with-dhcp/
+
+http://www.debian-administration.org/articles/591
+
+```shell
+nsupdate -v -k /etc/bind/admin-updater.key
+```
+
+```shell
+> update delete www.example.com cname
+> send
+
+> update add www1.example.com 86400 a 172.16.1.1
+> update add www.example.com 600 cname www1.example.com.
+> send
+```
+
+###### Ported from private Knowledge Base page 2010+ - should have had notes going back to 2003 but young guys don't document enough!