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title Zeroconf

How to compile

Compile me with:

pandoc --standalone --to=revealjs --output=README.html README.md --slide-level=2

Objectives

Preliminaries

  • Wide-area network (wan) vs local-area network (LAN)
  • Internet Protocol (IP)
    • Connectionless (delivers packets unreliably)
    • IP address (base 10)
    • Internal/external
  • Unicast vs broadcast
    • LAN Broadcast address 255.255.255.x

Traditional networking

  • DHCP delivers IP of some fixed things (including DNS)
  • DNS delivers IP of everything else

Example

  • Bob: Hey everone! I'm new here. Can I have 192.168.2.44?
  • DHCP server: Bob, yes you may have 192.168.2.44. Here is our networks DNS server 192.168.2.56
  • A few moments later
  • Bob: Hello DNS server (192.168.2.56), who is "printer.local"?
  • DNS server: Oh, that's 192.168.2.98

Ho to add a new printer?

  • Requires server admin
  • Server admin: [Plugs in printer to network]
  • Printer: Hey everyone! I'm new here. Can I have IP ...?
  • DHCP server: Printer, yes you may have ...
  • Server admin: DHCP server, what address did you give the printer?
  • DHCP server: ...
  • Server admin: DNS server, please send "printer2.local" to ...

Zeroconf

  • Idea: Use multicast IP address to send DNS request
  • Special semantics for *.local
    • "considered a problem by some members of the IETF"
  • Protocols: Multicast DNS (MDNS), Micro$oft's Link-Local Multicast Name Resolution
  • MDNS Clients: Apple Bonjour, Avahi (open), Systemd

Example

  • Bob: Hey everyone, who has "printer.local"?
  • Printer: I do.
  • Bob: Ok, noted.
  • Alice: I didn't ask, but ok. Also noted.

DNS Service Discovery (DNS-SD)

  • What if we don't know the domain-name of printer?
  • Broadcast a DNS request for PTR and TXT records
  • Service types in DNS-SD
  • Could use WS-Discovery instead of DNS-SD

Clients

  • Systemd (lol)
  • Others

Trust issues

  • Do you trust the entire network?
  • Attacker can learn your devices
  • Devices can lie

Other issues

  • Separate broadcast domains?
  • Name conflicts

Related ideas

  • Managed vs unmanaged service directory
    • Managed: LDAP, DNS, others
    • Unmanaged: mDNS, Bluetooth SDP
  • Service description language
  • Service mesh
  • Leader election