Slides for Chapter 9: Name Services From Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edition 4, Pearson Education 2005
Figure 9.1 Composed naming domains used to access a resource from a UR URL http://www.cdk3.net:8888/webexamples/earth.html DNS lookup Resource ID (IP number, port number, pathname) 55.55.55.55 8888 WebExamples/earth.html Network address 2:60:8c:2:b0:5a file Web server Socket
Figure 9.2 Iterative navigation NS2 Client 2 1 NS1 Name servers 3 NS3 A client iteratively contacts name servers NS1 NS3 in order to resolve a name
Figure 9.3 Non recursive and recursive server controlled navigation NS2 NS2 client 1 4 NS1 2 3 NS3 client 1 5 NS1 2 4 3 NS3 Non recursive server controlled Recursive server controlled A name server NS1 communicates with other name servers on behalf of a client
Figure 9.4 DNS name servers Note: Name server names are in italics, and the corresponding domains are in parentheses. Arrows denote name server entries ns1.nic.uk (uk) co.uk ac.uk a.root servers.net (root) uk purdue.edu yahoo.com ns0.ja.net (ac.uk) ns.purdue.edu (purdue.edu) *.purdue.edu ic.ac.uk qmw.ac.uk dcs.qmw.ac.uk *.qmw.ac.uk *.dcs.qmw.ac.uk *.ic.ac.uk alpha.qmw.ac.uk (qmw.ac.uk) dns0.dcs.qmw.ac.uk (dcs.qmw.ac.uk) dns0 doc.ic.ac.uk (ic.ac.uk)
Figure 9.5 DNS resource records Record type Meaning Main contents A A computer address IP number NS An authoritative name server Domain name for server CNAME The canonical name for an alias Domain name for alias SOA Marks the start of data for a zone Parameters governing the zone WKS A well known service description List of service names and protocols PTR Domain name pointer (reverse Domain name lookups) HINFO Host information Machine architecture and operating system MX Mail exchange List of <preference, host> pairs TXT Text string Arbitrary text
Figure 9.6 DNS zone data records domain name time to live class type value 1D IN NS dns0 1D IN NS dns1 1D IN NS cancer.ucs.ed.ac.uk 1D IN MX 1 mail1.qmul.ac.uk 1D IN MX 2 mail2.qmul.ac.uk domain name time to live class type value www 1D IN CNAME apricot apricot 1D IN A 138.37.88.248 dcs 1D IN NS dns0.dcs dns0.dcs 1D IN A 138.37.88.249 dcs 1D IN NS dns1.dcs dns1.dcs 1D IN A 138.37.94.248 dcs 1D IN NS cancer.ucs.ed.ac.uk
Figure 9.7 GNS directory tree and value tree for user Peter.Smith DI: 599 (EC) DI: 543 UK FR DI: 574 DI: 437 AC DI: 322 QMW Peter.Smith mailboxes password Alpha Beta Gamma
Figure 9.8 Merging trees under a new root Well known directories: #599 = #633/EC #642 = #633/NORTH AMERICA DI: 599 DI: 633 (WORLD) EC NORTH AMERICA DI: 642 DI: 543 UK FR DI: 574 DI: 732 US CANADA DI: 457
Figure 9.9 Restructuring the directory Well known directories: #599 = #633/EC #642 = #633/NORTH AMERICA DI: 599 DI: 633 (WORLD) EC NORTH AMERICA DI: 642 DI: 543 UK FR US DI: 574 DI: 732 US CANADA DI: 457 #633/EC/US
Figure 9.10 X.500 service architecture DUA DSA DSA DUA DUA DSA DSA DSA DSA
Figure 9.11 Part of the X.500 Directory Information Tree X.500 Service (root)... France (country)great Britain (country)greece (country)...... BT Plc (organization)university of Gormenghast (organization)...... Computing Service (organizationalunit) Department of Computer Science (organizationalunit) Engineering Department (organizationalunit)...... Departmental Staff (organizationalunit) ely (applicationprocess) Research Students (organizationalunit)...... Alice Flintstone (person)... Pat King (person)james Healey (person) Janet Papworth (person)...
Figure 9.12 An X.500 DIB Entry info Alice Flintstone, Departmental Staff, Department of Computer Science, University of Gormenghast, GB commonname Alice.L.Flintstone Alice.Flintstone Alice Flintstone A. Flintstone surname Flintstone telephonenumber +44 986 33 4604 uid alf mail alf@dcs.gormenghast.ac.uk Alice.Flintstone@dcs.gormenghast.ac.uk roomnumber Z42 userclass Research Fellow
Exercícios (Cap. 9) 1. Como a técnica de caching ajuda a disponibilidade de um serviço? 2. Qual a diferença entre navegação recursiva e iterativa? Qual das duas é mais eficiente em termos de velocidade de resposta e sobrecarga dos servidores? 3. Quando um servidor DNS provê várias respostas como resultado de uma consulta e porquê? 4. Qual a diferença entre X.500 e LDAP? (especificação x protocolo?)
Exercícios (Cap. 9) 5. Qual a semelhança entre as árvores de diretório do sistema de arquivos UNIX e a do serviço de diretórios GNS? 6. Qual a semelhança entre xpath e expressão do filtro para mecanismo de busca no X.500? 7. O que é uma entrada MX no DNS? 8. Explique a diferença entre: navegação recursiva controlada pelo servidor e navegação nãorecursiva controlada pelo servidor.
Exercícios (Cap. 6) 9. Conceitue Processo e Thread 10.Quais são as arquiteturas multi thread para servidores? (Thread por requisição...) 11.EXTRA (Cap. 7): A. Qual o papel de um Firewall? B. O que é criptografia? C. O que é chave em criptografia? D. O significa chave pública e privada? E. O que é criptografia simétrica e assimétrica? F. O que é autenticação?