INTERNET PROTOCOLS Class 9 CSCI 6433 David C. Roberts Entire contents copyright 2011, David C. Roberts, all rights reserved

Agenda Name systems DNS 2

Why Name Systems Computers are happy with numbers Important reasons why IP addresses have numbers However, humans like to deal with names Especially in the case of IPv6 Name systems can provide names for humans to deal with But theres another reason toonames can be made more persistent than IP addresses 3

Internet Name Spaces MAC Addresses Identities of NICs Unique across a LAN, at least Usually 48 bits IP Addresses Routable address of a host Can change frequently 32 or 128 bits Unique across the Internet Domain Names English language names Generally tied to an activity of people Changes slowly, may have years of duration 4

Internet with Names, without DNS 5

With DNS 6

Basic Name System Functions Name space: rules how names are structured and used Name registration: a method for linking specific names to specific devices so that names are unique across the entire Internet Name resolution: mechanism for translating a symbolic name into an IP address 7

Principal RFCs for DNS 8

Goals for DNS Global, scalable, consistent name space Local control over local resources Distributed design to avoid bottlenecks Application universality Support for multiple underlying protocols Hardware universality 9

DNS Functions 10

Name Space 11 Each node in the DNS tree is identified by a label

Name Syntax Length: each label can be up to 63 characters long Symbols: letters, numbers, dash are allowed Case: labels are not case-sensitive Every label must be unique within its parent domain 12

Domain Name Construction 13

Resource Specification Can specify a resource within a domain name by providing a directory structure after the name For example, could have Salt.crystal.rocks/Essay 14

Uniqueness Every label must be unique within its parent domain 15 Names can be up to 255 characters long

Management of the Name Space ICANN and IANA are responsible for management of the name space They delegate responsibility for parts of the name space to other organizations Different parts of the name space may be managed differently 16

Original TLDs.ARPA.COM.EDU.GOV.MIL.NET.ORG 17 The three TLDs for most names became very crowded very quickly

Current TLDs 18

Country Code TLD Authorities Each country has authority to set up and manage its TLD Many country codes have been defined Country codes have two letters Some country codes are used for other purposes Some TLDs are restricted Examples: Scoop.It uses TLD for Italy to spell scoop it Bit.ly spells out bitly using TLD for Lybia 19

DNS Name Servers Each DNS server is a database server Resource record stores a type of information about a node in the DNS tree. It has general format for part of record, specialized format for information for its type Master file representation is text representation for resource record, editable by humans 20

RR Types 21

Root Name Servers Today there are 13 different root name servers Each of these has multiple physical servers 22

DNS Resolvers Functions: Standard name resolution: given a DNS name, find the IP address Reverse name resolution: take an IP address and determine what name is associated with it Electronic mail resolution: determine where to send based on the address used in a message Actions: Provide user interface: allow name to be used in place of IP address Forming and sending queries: sends queries to DNS Processing responses: accept response from DNS, decide what do with it 23

Iterative Resolution 24

Recursive Resolution 25

DNS Resource Records and Classes Each DNS server is a type of database server The database has entries called Resource Records for domains RRs are stored in binary but have text versions that are shown to humans 26

Common DNS Resource Records 27

Caching Caching is very important to DNS Names that are referenced are often referenced again There is extensive caching at all levels of DNS When a cached value is returned, the address of the authoritative server is also returned Each RR has a TTL specified. Servers that cache the record discard it when the time interval expires 28

DNS Message Format 29

Details 30

Examples of Object Types 31

Persistence Persistence of DNS names and IP addresses is different How? 32

Summary DNS is a crucial Internet service It allows names to be established for persistent areas of influence The convenience of names is secondary to its importance DNS is the Internet name space that best represents human activities 33