The document discusses Zero Configuration Networking (zeroconf), a protocol that simplifies the addition of devices to a local area network (LAN) without the need for manual configuration. Key features include automatic IP address assignment, naming through multicast DNS, and service discovery protocols to locate services within the network. It highlights the importance of simplicity in design and provides insights into implementation through various tools and technologies.

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Zero Configuration
Networking
by
Zafar Shahid
Oct. 8 2017
Silicon Valley Code Camp, San Jose CA

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Have you heard the term ZERO-CONF ?Have you heard the term ZERO-CONF ?
1394
DVD and HDTV /
Display
Audio Jukebox
Tablet
100BaseT
802.11a+e+g
AP
Home PlugPrinter
Laptop

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Let us Imagine…Let us Imagine…
A service/device is added to LAN, and it is working
without installation. For example:
Refrigerator
Surveillance camera
Printer
Chat service
File service
All the computers has an updated list of services/
devices.
In short:
Must have for home LANs and Ad-hoc Networks.

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Concept
Zero Conf Stack
Addressing
Naming
Browsing
USB vs Ethernet
Conclusion
AgendaAgenda

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Plug and Play on LANPlug and Play on LAN
Just like Electric LampJust like Electric Lamp
On Wide area networks, we can communicate to
servers without much problem.
Wide area networks were mature since long. E.g.
email server, web server etc.
On Local area networks, it is not that easy. Just
connect two laptops using an ethernet cable using
hub, and try to make communication between them.
ZeroConf is a protocol stack which makes Services
on LAN plug and play.
Apple has done it 30+ years ago in AppleTalk, but
somehow it was missing in IP community

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Challenge: SimplicityChallenge: Simplicity
Any body can make a complicated product. The real
challenge is to make a simple product.
Once that cannot be broken in any scenario, on any
platform etc.
Protocol Design principle:
In protocol design, perfection has been reached:
not when there is nothing left to add,
but when there is nothing left to take away
RFC 1925 The Twelve Networking Truths

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Plug n play - HowPlug n play - How
Addressing:
First you need IP address.
Naming:
Human being don't like numbers, we need names.
Browsing:
IP networks don't have browsing.
Non-trivial part of the zero-conf stack.
More than Dozen technologies were proposed for
browsing, but they failed, because they were
complicated.

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AddressingAddressing
Automatic IP address assignment.
Pick random IP address from IPv4LL
ARP if anyone else is using it.
Perform conflict resolution if anyone is using it.
No DHCP server needed
Link-local addresses
IPv4 169.254.0.0/16
IPv6 FE80::/64
RFCs
RFC 3927 IPv4LL
RFC 2462 IPv6

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NamingNaming
Once addressing is done, computers can talk to each
other, but human likes names.
Multicast DNS (mDNS) - Extension to well known
DNS protocol
Same Query syntax
Same Packet format
Same naming and record types.
Similar to addressing where 169.254/16 is reserved
for LL. “.local” TLD is reserved for ZeroConf.
www.multicastdns.org

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NamingNaming
Pick desired name in .local TLD ( Top level domain. E.g.
zafarLaptop.local
Issue query to see if anyone else is using it by
multicasting it over the network.
If someone else is using it, try another.
Muilcast addresses:
IPv4 224.0.0.251
IPv6 FF02::FB
.local TLD is free so you don’t have to pay annual fee to
keep it.
Anyone can take any name.

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Browsing – Discovery protocolsBrowsing – Discovery protocols
So far, we have achieved addressing and naming
successfully using existing technologies.
But it we mis-type a name or don’t know the name, no
body is there to correct. So we need a browsing or
discovery protocol.
Historically there have been many tries but all
failed, probably because the protocols were too
complicated.
It is less obvious BUT possible to do Service
discovery using semantics of DNS protocols.

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Service Discovery using DNSService Discovery using DNS
We use some of the semantics of DNS in newer ways.
Multiple answers: IP can return multiple addresses. If
you have MULTI-HOMES hosts, you will get back
multiple address This is normal.
PTR records: performs reverse DNS, from addresses
to hostname.
SRV records (RFC 2782): returns the port number. If
directory service could tell you that number, then you
don't need it.

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Service Discovery – Three basic operationsService Discovery – Three basic operations
Register: register the service you are offering.
Browse : Client can browse for all the available
services.
Resolve(at time of service): .local name to IP
address. Names are persistent, but addresses are
not.
Service discovery does not find addresses. It finds
names. And at time of use, we resolve names to
addresses.

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DNS Service Discovery - ExampleDNS Service Discovery - Example
A computer wants to know the printers are on the LAN:
PTR DNS query: (multicast)
_ipp._tcp.local PTR
Response:
Sales._ipp._tcp.local
Marketing._ipp._tcp.local
Engg._ipp._tcp.local
2nd
floor QA._ipp._tcp.local // spaces allowed
Components of Service Name:
User-Visible Name:User-Visible Name: 2nd floor QA2nd floor QA._ipp._tcp.local.._ipp._tcp.local.
Service Type/Service Protocol Name: 2nd floor QAService Type/Service Protocol Name: 2nd floor QA._ipp._ipp._tcp.local.._tcp.local.
Domain: 2nd floor QA._ipp._tcp.Domain: 2nd floor QA._ipp._tcp.locallocal..

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LOOKUP via DNS SRVLOOKUP via DNS SRV
Let us connect to Engg printer Engg._ipp._tcp.local,
we will make the following calls:
Sales._ipp._tcp.local SRV
=> 0 0 30000 myprinter.local (port 30000)
Sales._ipp._tcp.local TXT
=> pdl=application/postscript (name/value pair.
myprinter.local A =>169.254.12.34
DNS-SD Availability
Use apple's Darwin open source
Very portable around ~20k lines of code.

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Avoiding ChattinessAvoiding Chattiness
AppleTalk was too chatty. We have taken measure to
make ZeroConf less chatty.
Aggressive caching //opportunistic caching for later
use.
Duplicate Suppression section in Queries.
Duplicate answer suppression
Duplication question supperession
Exponential query backoff.
TTL is too long.

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Joining/Leaving networkJoining/Leaving network
If new service joins, it announces itself.
If service leaves:
Shorter TTL will put un0necessary load.
So we go the other way, we use connection failure- as a
hint.
Other clients also witness this connection-failure over the
network
If resolve() fails => PTR record is reconfirmed.
If reconfirm fails =? Record removed from browser list. –
When other clients observe failed queries – They also
remove records from their lists.

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ImplementationImplementation
Bonjour on Mac/Windows
Avahi on Linux
Also available on Android.

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USB vs. EthernetUSB vs. Ethernet
Plug n play
Power
With Ethernet cable
Power over ethernet
Plug n play with Zero conf
Plus, can even work with 100 meter cable.
And have speed of gbps
So if we have all ZeroConf well in time, we might not
need USB interface at all.

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ConclusionConclusion
It is difficult to imagine a network deviceIt is difficult to imagine a network device
without ZeroConf capability.without ZeroConf capability.

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DemoDemo
Bonjour BrowserBonjour Browser
TeamViewerTeamViewer
DNS-SD cmd lineDNS-SD cmd line
WebcamWebcam
WiresharkWireshark