Names & Addresses. Names & Addresses. Names vs. Addresses. Identity. Names vs. Addresses. CS 194: Distributed Systems: Naming

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1 Names & Addresses CS 9: Distributed Systems: Naming Computer Science Division Department of Electrical Engineering and Computer Sciences University of California, Berkeley Berkeley, CA What is a? What is an address? What is the difference between s and addresses? EECS - UCB Names & Addresses Names vs. Addresses Name: string of bits that refer to an entity E.g., your Address: string of bits that have location semantics E.g., your home address, your phone # Voyager address Seven-of-Nine Borg Weather a string is is a or or address may depend on context Names vs. Addresses Identity address Florence Name that uniquely identify an entity E.g., your SSN Identifier properties: An identifier refers to at most one entity Each entity is referred to by at most one identifier An identifier always refers to the same entity (i.e., it is never reused) Leonardo da Vinci City of Vinci

2 Addresses: Internet Centric View Says how to reach an object it has location semantics associated to it Usually, a format easy to process by computers Name: Does not have any location semantics associated to it Usually, a format easier to understand/read/remember by people Examples: IP address: Name: arachne.berkeley.edu Name Service Name space: define the set of possible s and their relationship Hierarchical (e.g., Unix and Windows file s) Flat Bindings: the mapping between s and values (e.g., addresses or other s) Bindings can be implemented by using tables Resolution: procedure that, when invoked with a, returns the corresponding value Name server: specific implementation of a resolution mechanism that is available on the network and that can be queried by sending messages Binding and Resolution in the Internet In general there are multiple mappings Host : arachne.berkeley.edu DNS resolution IP address: ARP (Address Resolution Protocol) Ethernet MAC address: Mapping Multiple s can map onto the same address Example: and arachne.berkeley.edu maps to the same machine (i.e., the same IP address) One can map onto multiple addresses Example: can be mapped to multiple machines Name Space Linking and Mounting () A general naming graph with a single root node directory node Named entity Symbolic link in a naming graph

3 Linking and Mounting () Mounting remote spaces through a specific process protocol Linking and Mounting () Organization of the DEC Global Name Service Domain Name System (DNS) Hierarchy() root edu com gov mil org net uk fr berkeley cmu eecs sims sonoma DNS Hierarchy () Unique domain suffix is assigned by the Internet Authority The domain administrators have complete control over the domain No limit on the number of subdomains or number of levels Name space is not related with the physical interconnection Geographical hierarchy is allowed (e.g., cnri.reston.va.us) A could be a domain or an individual objects DNS Top Level Domains DNS Name Servers Domain Name com edu gov mil net org country code Assignment Commercial Educational Government Military Network Other organizations au, uk, ca, Why not centralize DNS? Single point of failure Traffic volume Distant centralized database Maintenance Doesn t scale!

4 Server Hierarchy: Zones A zone corresponds to an administrative authority that is responsible for that portion of the hierarchy berkeley root edu com gov mil org net uk fr cmu Server Hierarchy Server are organized in hierarchies Each server has authority over a portion of the hierarchy A single node in the hierarchy cannot be split A server maintains only a subset of all s It needs to know other servers that are responsible for the other portions of the hierarchy eecs sims divine Server Hierarchy Authority: each server has the to address translation table for all s in the space it controls Every server knows the root Root server knows about all top-level domains DNS Name Servers No server has all -to-ip address mappings Local servers: Each ISP (company) has local (default) server Host DNS query first go to local server Authoritative servers: For a host: stores that host s (, IP address) Can perform /address translation for that host s DNS: Root Name Servers Simple DNS Example Contacted by local server that can not resolve Root server: Contacts authoritative server if mapping not known Gets mapping Returns mapping to local server ~ Dozen root servers worldwide Host whsitler.cs.cmu.edu wants IP address of. Contacts its local DNS server,. contacts root server, if necessary. Root server contacts authoritative server, ns.berkeley.edu, if necessary root server local server authorititive server ns.berkeley.edu

5 Root server: May not know authoritative server May know intermediate server: who to contact to find authoritative server? DNS Example local server 8 root server 7 intermediate server (edu server) authoritative server ns.berkeley.edu Recursive query: Puts burden of resolution on contacted server Heavy load? DNS: Iterated Queries Iterated query: local server Contacted server replies with of server to contact 8 I don t know this, but ask this server root server iterated query intermediate server (edu server) 7 authoritative server ns.berkeley.edu