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Naming

Naming. CSCI 4780/6780. Name Space Implementation. Naming service – A service that lets users to add/delete and lookup names In large distributed systems naming service has to be distributed For convenience namespace is partitioned into logical layers

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Naming

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  1. Naming CSCI 4780/6780

  2. Name Space Implementation • Naming service – A service that lets users to add/delete and lookup names • In large distributed systems naming service has to be distributed • For convenience namespace is partitioned into logical layers • Global layer – Highest level nodes (root and first level children) • Administration layer – Directory nodes managed by single organization (Ex: Departmental nodes in UGA) • Managerial layer – Nodes of local network, shared files, etc.

  3. Name Space Distribution • An example partitioning of the DNS name space, including Internet-accessible files, into three layers.

  4. Layers and their Characteristics • Global layer • Stability – Directory tables rarely change • High availability is critical • Permits high levels of caching, throughput is critical • Administrative Layer • Availability is critical • Permits high levels of caching • Response time should be fast • Managerial level • Client-side caching is in general less effective • Fast response time is crucial

  5. Comparison of Layers

  6. Name Resolution - Implementation • Distribution affects name resolution implementation • Example: root:<nl, vu, cs, ftp, pub, globe, index.txt> • Two types – Iterative process and Recursive Process • Iterative Process • Each node resolves as much as it can and sends result to client, which contacts the next level of node • Recursive Process • Nodes do not return intermediate results to client • Contact next level of nodes obtain addresses and send complete results to the client

  7. Iterative Name Resolution

  8. Recursive Name Resolution (2)

  9. Iterative Vs. Recursive Name Resolutions • Iterative • Shorter connection durations -> Less load on servers • Less effective caching -> High latency • Recursive • Longer connection duration -> High loads on servers • Permits caching at higher levels of nodes • High-level nodes can “learn” about lower level nodes • Permits shortcuts • Cheaper with respect to communication latency

  10. Caching in Recursive Name Resolution • Recursive name resolution of <nl, vu, cs, ftp>. Name servers cache intermediate results for subsequent lookups.

  11. Implementation of Name Resolution • The comparison between recursive and iterative name resolution with respect to communication costs.

  12. The Domain Name Service • Largest distributed naming service • Used for looking up host addresses and mail servers • Hierarchically organized as a rooted tree • Labels – 63 Characters; Pathnames – 256 characters • String representation – Listing labels from right to left separated by dots • Domain – Subtree of nametree • Domain name – Path to the root of the domain • Contents of node – Resource records

  13. The DNS Name Space • The most important types of resource records forming the contents of nodes in the DNS name space.

  14. DNS Implementation • DNS namespace is divided into global layer and administration layer • Managerial layer not part of DNS • Each zone implemented by a name server • Replicated for availability • Updates happen only at primary name server • Lazy replication – Zone transfer • Database is made up of collection of files

  15. DNS Implementation - Example • An excerpt from the DNS database for the zone cs.vu.nl.

  16. Reference to Subdomains • Part of the description for the vu.nl domain which contains the cs.vu.nl domain.

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