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Naming III

Naming III. CSE 5306 Lecture Quiz 14 Due at 5 PM Thursday, 25 September 2014. 5.3.4 Domain Name System. The Internet Domain Name System (DNS) is the world’s largest distributed naming service. It swaps IP addresses for human-friendly URLs. It’s performing well after 30 years of service!

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Naming III

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  1. Naming III CSE 5306 Lecture Quiz 14 Due at 5 PM Thursday, 25 September 2014

  2. 5.3.4 Domain Name System • The Internet Domain Name System (DNS) is the world’s largest distributed naming service. • It swaps IP addresses for human-friendly URLs. • It’s performing well after 30 years of service! • Its designer had a deep understanding of how to make things simple.

  3. The DNS Name Space • The DNS example flits.cs.vu.nl. has... • Dots separating the labels; i.e., node names. • 1 to 63-character labels. • 1 to 256-character total length. • Its tree root on the right with optional trailing dot. • Any subtree is called a domain, and the path name to a domain’s root (e.g., root:<nl, vu, cs, flits>) is called a (relative or absolute) domain name. • Every node has a collection of resource records (above): • The start of authority (SOA) identifies the host, admin, etc. • MX identifies the zone’s mail server; e.g., zephyr.cs.vu.nl. • SVR identifies a server record; e.g., _http._tc.cs.vu.nl. • NS identifies the zone’s name server. • CNAME lists the zone’s canonical name and its aliases. • PTR records contain pointers to host names indexed on IP addresses.

  4. DNS Implementation • Each local zone’sprimary name servers manage DNS’ managerial layer, which lies beneath its global and administrational layers. • Secondary name servers regularly request “zone transfer” copies of all files that make up its local DNS database. • One of those files (above) identifies the node and zone names, the zone’s name server, mail servers, its Web and FTP servers, etc.

  5. Decentralized DNS Implementation • Scaling up to a million leaf DNS record servers requires decentralization: • Hashing each DNS name enables quick IP address lookups. • Mapping DNS to a distributed hash table (e.g., Chord, CoDoNS) distributes the lookup processes. • Solving the Zipf-like equation on p.216 reveals: • Only the x0 = 70 most popular DNS records need be replicated among the highest-level (0th-level) nodes. • The x1= 3306 next-most popular are replicated at 1. • The x2= 155,769 next-most popular are replicated at 2.

  6. R U O K ? • Which of the following does NOT accurately characterize the Internet’s Domain Name System? __ • DNS is the world’s largest distributed naming service. • It swaps IP addresses for human-friendly URLs. • Its designer had a deep understanding of how to make things simple. • But after 30 years of distinguished service, it is ready for a redesign.

  7. R U O K ? Match the following DNS terms with their definitions below. 2. Root. __ 7. SOA. __ 3. Node name. __ 8. MX. __ 4. Domain. __ 9. NS. __ 5. Domain name. __ 10. CNAME. __ 6. Resource record. __ 11. PTR. __ • Categorized list of zone resource names. • Identifies zone’s host, admin, etc. • The “vu.nl” in flits.cs.vu.nl. • The “nl” in flits.cs.vu.nl. • Thestring root:<nl, vu, cs, flits> • Identifies zone’s mail server. • The zone’s primary name and its aliases. • The “vu” in flits.cs.vu.nl. k. Points at the host name that corresponds to given IP address. • Identifies the zone’s name server.

  8. R U O K ? 12. True or False: Each local zone’s primary name servers manage DNS’ (lowest) managerial layer, keeping distributed secondary name servers apprised of all changes as they happen. __ • True. • False.

  9. R U O K ? 13. Assuming α = 0.9, b = 32, a 10K node network and 1M DNS records, how many DNS records should be replicated at the lowest level for C = 2 hops? __ • 1 b. 57 c. 2.7K d. 127K e. 130K.

  10. 5.4 Attribute-Based Naming • In addition to having human-friendly names, every entity needs advertise its contents to facilitate searches. • Attribute-based naming requires Websites to provide lists of (attribute, value) pairs. • Web surfers provide similar lists to find the entities, whose pairs are most similar to their own.

  11. 5.4.1 Directory Services • Naming systems support structured naming, like DNS’ human-friendly URLs. • Directory services are systems that support attribute-based searches. • Humans must choose (attribute, value) pairs manually; even then, diverse groups of people disagree. When Enya’s songs didn’t fit any genre, she invented “New Age” (?) music. • The resource description framework (RDF) helps by adding a verb to the pair; e.g., (subject, predicate, object) = (person, name, Alice). Each of the 3 can be a resource; e.g., (URL, text string description, filename). • The lengthy named resources typically are stored a far away. This accounts for the Google cloud’s instant report that it has found “thousands of matches,” but only 10 URLs are displayed, and no resource is opened.

  12. 5.4.2 LDAP’s Hierarchy • Structured and attribute-based naming combine nicely in the lightweight directory access protocol (LDAP). • Like DNS’ resource records (slide 4’s figure), LDAP collects (attribute, value) pairs, but its values are arrays and lists (see “Mail_Servers” above). • LDAPs’ collection is called a directory information base (DIB). Each globally unique attribute is a relative distinguished name (RDN); e.g., / C=NL / O=VrijeUniversiteit / OU=Comp. Sc.

  13. LDAP’s Hierarchy (continued) • As in DNS, the RDNs listed in sequence form a hierarchical directory information tree (DIT) of directory-entry nodes, each of which is an LDAP record and a directory (see node N above) in the traditional sense. • Like UNIX’ cd and ls commands, LDAP’s read operation fetches the named node’s record (slide 8’s figure), and its list operation displays the names of all of the node’s outgoing (child) edges. • The DIT is distributed among many directory service agent (DSA) servers. Clients’ directory user agent (DUA) proxies resolve structured names, and they collaborate with DSAs on attribute-based DIB searches. For example, answer = search(“&(C=NL)(O-VrijeUniversiteit)(OU=*)(CN=Main Server)”) • Microsoft’s Active Directory has a forest of LDAP directory trees, and a global catalog that begins each search in a particular tree. • Grid computing’s recent universal directory and discovery integration (UDDI) blends a simplified LDAP with DNS.

  14. R U O K ? 14. Which of the following is a plausible attribute-based naming pair? __ • (running, shoes) • (houseCat, beagle) • (emailSender, BroSteve) • All of the above. • None of the above.

  15. R U O K ? Match the following terms with their definitions below. 15. Naming system. __ 16. Directory service. __ 17. Resource description framework. __ 18. Zone transfer. __ 19. Zipf-like distribution. __ • Primary name servers regularly write entire local DNS database to secondary name servers. • Systems that support attribute-based searches. • Supports structured naming; e.g., DNS’ human-friendly URLs. • Frequency distribution of similar Web searches. • Extends attribute-based naming to (subject, predicate, object) = (person, name, Alice).

  16. R U O K ? Match the following hierarchical implementation terms with their definitions below. 20. Lightweight directory access protocol. __ 21. Directory information base. __ 22. Relative distinguished name. __ 23. Directory information tree. __ 24. Directory service agent. __ 25. Directory user agent. __ • A guaranteed globally unique attribute. • A hierarchy of directory-entry nodes, each of which is an LDAP record. • A combination of structured and attribute-based naming. • Many servers among which the DIT is distributed. • LDAPs’ collection of (attribute, value) pairs. • A server that resolves a client’s structured name, before collaborating with a DSA on an attribute-based search.

  17. R U O K ? 26. Which of the following does NOT accurately describe LDAP? __ • LDAP combines structured and attribute-based naming. • LDAP collects (attribute, value) pairs like DNS resource records. • LDAP calls its collection (attribute, value) pairs a directory information base. • Grid computing’s recent universal directory and discovery integration (UDDI) blends a simplified LDAP with DNS.

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