Naming and Addressing

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1 Naming and Addressing Sanjeev Setia 9/14/99 INFt 803 Fall '99 1

2 Outline URI,URN,URL,URC, Functional requirements [RFC 1737] Knoxville framework for URNs DNS-based URI resolution 9/14/99 INFt 803 Fall '99 2

3 URIs URN persistent name: identifies a resource or unit of information URL identifies the location or container for an instance of a resource identified by a URN identify the host to contact and protocol to use, e.g. URC (UR characteristic) meta-data (owner, encoding, access list, etc.) 9/14/99 INFt 803 Fall '99 3

4 Functional Requirements Global scope same meaning everywhere Global uniqueness Persistence Scalability Legacy support Extensibility 9/14/99 INFt 803 Fall '99 4

5 Functional Requirements cont d Independence solely responsibility of naming authority to determine conditions under which it will issue a name Resolution there must be some feasible mechanism to translate a URN into a URL 9/14/99 INFt 803 Fall '99 5

6 URN encoding requirements Single encoding simple comparison human transcribability transport friendliness machine consumption text recognition 9/14/99 INFt 803 Fall '99 6

7 Implications for URNs To satisy uniqueness & scalability, name assignment is delegated to naming authorities name of top-level authorities are persistent, globally unique, centrally registered Naming authorities that support scalable naming are encouraged Strongly recommended that there be a mapping between URNs generated by a naming authority and URLs mapping need not be provided by naming authority necessary to limit character set usable in URNs 9/14/99 INFt 803 Fall '99 7

8 Knoxville framework framework distinguishes between naming schemes and resolution systems naming scheme: procedure for creating and assigning unique URNs according to a specified syntax resolution system: a network-accessible service that stores URNs and resolves them independence between naming scheme and resolution system naming scheme not tied to a particular resolution system 9/14/99 INFt 803 Fall '99 8

9 Knoxville framework cont d mechanisms need to be created so that the user of a URN can discover what resolution systems are able to resolve the URN URN registry URN syntax naming scheme identifier followed by a colon and a string that has a naming scheme-specific syntax urn:hdl:cnri.dlib/august95 urn:lifn:some.domain:anything-goes-here urn:path:/a/b/c/doc.html urn:inet:library.bigstate.edu:aj17-mcc 9/14/99 INFt 803 Fall '99 9

10 DNS-based URI resolution Maps internet hostnames to IP addresses widely deployed and understood however, not appropriate to use DNS to maintain information for each resource never intended to handle that many records limited record size domain names are not appropriate as URNs therefore, use DNS to locate resolvers that can provide information on a particular resource 9/14/99 INFt 803 Fall '99 10

11 Approach Introduce a new DNS record: NAPTR Rewrite the URI into a domain name following rules specified in the NAPTR record NAPTR fields order, preference, flags service (specifies resolution protocol and service available if rewrite is applied) regexp (sed-like substitution expression) replacement Rules applied by client not server 9/14/99 INFt 803 Fall '99 11

12 Approach cont d First known key has a first known key of http.uri.net urn:foo:1234 has a first known key of foo.urn.net Services I2L, I2R, I2Rs, I2C, I2N Protocols used for communicating with resolver service 9/14/99 INFt 803 Fall '99 12

13 Example 1 urn:duns: :annual-report-1997 lookup NAPTRs for duns.urn.net duns.urn.net order pref flags service regexp replac IN NAPTR s dunslink+i2l+i2c dunslink.udp.isi.com IN NAPTR s thttp+i2l+i2c+i2r thttp.tcp.isi.com s flag denotes next lookup should be for SRV records, a for A records looking up SRV records for thttp.tcp.isi.com will return hosts that can be contacted plus which port the thttp server is listening on 9/14/99 INFt 803 Fall '99 13

14 Example 2 urn:cid:199940@mordred.gatech.edu lookup NAPTR for cid.urn.net cid.urn.net order pref flags service regexp repla IN NAPTR /urn:cid:.+@([^\.]+\.)(.*)$/\2/i. Substitution expression returns string gatech.edu lookup NAPTR for gatech.edu gatech.edu IN NAPTR s rcds+i2l+i2c _rcds._udp.gatech.edu 9/14/99 INFt 803 Fall '99 14

15 Example 3 lookup http.uri.net http.uri.net IN NAPTR ! lookup IN NAPTR s thttp+l2r _thttp._tcp.foo.com looking up SRV records for thttp.tcp.foo.com should return information on hosts that are mirror sites for foo.com 9/14/99 INFt 803 Fall '99 15

Request for Comments: Xerox Corporation December Functional Requirements for Uniform Resource Names

Request for Comments: Xerox Corporation December Functional Requirements for Uniform Resource Names Network Working Group Request for Comments: 1737 Category: Informational K. Sollins MIT/LCS L. Masinter Xerox Corporation December 1994 Status of this Memo Functional Requirements for Uniform Resource