... 1. 1. Contacts its local DNS server, Contacts its local DNS - PDF document

✚ ❈ ● � � ❋ ❊ ❉ ❇ ● � � ❆ ❅ ✶ ✻ ❈ ❈ ✶ ✂ ✄ � � ☎ ✁ ✂ ❃ ● ❖ ❍ ❆ ✄ ✄ ❍ ✽ � � ✄ ✚ ✛ ✄ ✄ ✄ ✎ ✄ ✚ ✛ ✚ ✄ ✄ ✄ ✆ � ☛ � ✚ ✚ ✚ ☎ ✄ ✚ ✕ � ✚ � ✛ � ✚ � ☎ � ✄ ✄ ✁ ✄ � � ❖ ✽ ✄ ✂ ❅ � � � � ✄ DNS: Domain Name System Application Layer in the Domain Name System: Domain Name System: Internet People: People: many identifiers: many identifiers: SSN, name, Passport # distributed database implemented distributed database implemented SSN, name, Passport # �������������������� �������������������� in hierarchy of many name servers in hierarchy of many name servers Internet hosts, routers: Internet hosts, routers: application-layer protocol application-layer protocol host, host, IP address (32 bit) - used IP address (32 bit) - used routers, name servers to routers, name servers to for addressing for addressing datagrams datagrams ✁ name communicate to resolve communicate to resolve names names ✂ , e.g., name , e.g., (address/name translation) (address/name translation) harmony.cs cs. .huji huji.ac. .ac.il il - - harmony. used by humans used by humans note: core Internet function note: core Internet function implemented as application- implemented as application- Q: map between IP addresses Q: map between IP addresses layer protocol layer protocol and name ? and name ? ✁ edge complexity at network complexity at network ☎ s s edge 29 March, 2002 1 29 March, 2002 The Computer Communications Course 2 DNS name servers DNS: Root Name Servers no server has all name-to-IP no server has all name-to-IP ✝✟✞✡✠☞☛✟✌✍✝☞☛✟✎✡✏✒✑✔✓✖✕ ✞✗✝✟✌✡✕✗✠✟✌✍✘✙✎ address mappings address mappings Why not centralize DNS? Why not centralize DNS? ✎✡✛✟✜✟✎✢✛✣☛☞✤✍✌✔☛✥✝✟✌✗✠✦✠✟✞✍☛ Local name servers: Local name servers: single point of failure single point of failure ✞✢✕ ✜☞✎✖✠✟✌✗✘✙✎ each ISP, company has local each ISP, company has local traffic volume traffic volume ✞✔✞✍☛✥✠☞✌✍✘✙✎ ✎✡✛✟✜✟✎✡✛✔✧ (default) name server (default) name server distant centralized database ✝✟✞✡✠☞☛✟✌✍✝☞☛ distant centralized database host DNS query first goes to host DNS query first goes to ✌✔★✔☛☞✤✍✞✗✛✔✩ ✌✍☛✔✩ ✜✟✎✒✠✟✌✗✘✙✎ maintenance maintenance local name server local name server ✎✡✛✟✜✟✎✢✛✪✩ ✫✬✠✟✌✍✘✙✎ Authoritative name server: Authoritative name server: ✘✙✌✍✭✍✭✡✩ ✠☞✮✬✠✟✞✍☛✪✯✔✠✟✞✍✰✙✠ ✆ t doesn t scale! scale! ✮✱✎✡☛ ✘✙✌✗✭✔✭✡✩ ✠☞✮ doesn ☎ s for a host: stores that host for a host: stores that host s ✎✗☛✟★✍✛✱✠ ✘✙✌✗✭✔✭✡✩ ✠☞✮✪☛✟✞ IP address, name IP address, name ✞✗✝☞✌✡✕✗✠✟✌✍✘✙✎ ✎✡✛✟✜✟✎✡✛ can perform name/address can perform name/address ☎ s ✲✖✏✗✞✗✳☞✎✴✠✥✛ ✞✔✞✍☛✪✠✟✌✍✘✙✎ translation for that host translation for that host s ✎✡✛✟✜✟✎✢✛ ✰✵✞✗✛✔✕ ✏✗✰✙✩ ✏✍✎ name name 29 March, 2002 The Computer Communications Course 3 29 March, 2002 The Computer Communications Course 4 Domain Name Servers Simple DNS example ❁☞❁✟✻❂✽ ❃✱❄✵✷❀✺ ✷✔✶ ✷✔✶ root root root root Host Host harmony. harmony.cs cs. .huji huji.ac. .ac.il il 2 4 wants IP address of wants IP address of 3 gaia gaia. .cs cs. .umass umass. .edu edu 5 ... 1. 1. Contacts its local DNS server, Contacts its local DNS server, nsf.gov purdue.edu huji.ac.il co.il shuldig shuldig. .cs cs. .huji huji.ac. .ac.il il 2. shuldig 2. shuldig. .cs cs. .huji huji.ac. .ac.il il contacts root name server, if contacts root name server, if ❁✱P ❃✱❄✵✷❀✺ ✷✔✶ ✷✍✶ ■❑❏ ▲✡■◆▼ ■✟❋ ■✟❋ necessary necessary shuldig.cs.huji.ac.il dns.umass.edu cs.purdue.edu math. cs. 3. root name server contacts 3. root name server contacts 1 6 authoritative name server, authoritative name server, huji. huji. dns. dns .dmass dmass. .edu edu, , if necessary if necessary ac. ac. il il ✷✱✸☞✹ ✷✱✺ ✻☞✼ ✾❀✿✱❁☞✺ gaia.cs.umass.edu harmony.cs.huji.ac.il 29 March, 2002 The Computer Communications Course 5 29 March, 2002 The Computer Communications Course 6