Transcript Naming - Wichita State University

Applications
Outline
Name Service (DNS)
Traditional Applications
Naming
Outline
Terminology
Domain Naming System
Distributed File Systems
Overview
• What do names do?
–
–
–
–
–
identify objects
help locate objects
define membership in a group
specify a role
convey knowledge of a secret
• Name space
– defines set of possible names
– consists of a set of name to value bindings
Properties
• Names versus addresses
• Location transparent versus location-dependent
• Flat (indvisible) versus hierarchical (Unix file
name)
• Global versus local
• Absolute versus relative
• By architecture versus by convention
• Unique versus ambiguous
DNS
• The domain name system (DNS) is the way that
Internet domain names are located and translated
into Internet Protocol addresses.
• A domain name is a meaningful and easy-toremember "handle" for an Internet address.
• Because maintaining a central list of domain
name/IP address correspondences would be
impractical, the lists of domain names and IP
addresses are distributed throughout the Internet in
a hierarchy of authority.
Examples
• Hosts
kira.cs.twsu.edu
156.26.10.236
156.26.10.236
00:C0:F0:30:DC:8F
• Files
/usr/llp/tmp/foo
(server, fileid)
• Users
Larry Peterson
[email protected]
Examples (cont)
• Mailboxes
2
cs.princeton.edu
Name
server
User
1
user @ cs.princeton.edu
Mail
program
192.12.69.5
192.12.69.5
3
4
TCP
192.12.69.5
5
IP
• Services
nearby ps printer with short queue and 2MB
Domain Naming System
• Hierarchy
edu
princeton … mit
cs
com
gov
cisco… yahoo nasa …nsf
ee physics
ux01 ux04
• Name
kira.cs.twsu.edu
mil
org
arpa …navy
acm …ieee
net
uk
fr
Name Servers
• Partition hierarchy into zones
edu
princeton … mit
cs
ee
com
gov
cisco … yahoo nasa … nsf
mil
org
arpa … navy
acm … ieee
net
uk
fr
physics
ux01 ux04
• Each zone implemented by
two or more name servers
Root
name server
Princeton
name server
CS
name server
…
…
EE
name server
Cisco
name server
Resource Records
• Each name server maintains a collection of resource records
which consists of five components:
(Name, Value, Type, Class, TTL)
– A Resource record starts with a domain name, usually a fully
qualified domain name (A domain name that extends all the way
back to root. gomer.gimboid.com. is an FQDN.)
– Second is the record value. It depends on record type.
• IP addresses
• If the record data includes a domain name that is not a Fully Qualified
Domain Name it goes through the same appending process as the
domain name at the start of the record.
– Third is the record type: CNAME, PTR, A, etc.
– Fourth is the Record class: Internet, Hesiod, or Chaos
• Hesiod is only used at M.I.T, and maybe not even there anymore.
• Chaos is almost extinct.
– Fifth is the TTL, in seconds.
– Many servers will permit comments as a sixth component.
Resource Records
• Type
– NS: Value gives domain name for host running name server that
knows how to resolve names within specified domain.
– CNAME: Value gives canonical name for particular host; used to
define aliases.
– MX: Value gives domain name for host running mail server that
accepts messages for specified domain.
– A: indicates the value is an IP address.
• Class: allow other entities to define types. Only widely
Class is the one used by the Internet denoted as IN.
• TTL: Time To Live, the number of seconds
remaining on a cached record before it is purged.
DNS
• A Canonical Name (CNAME) is a host's official
name as opposed to an alias.
– The official name is the first hostname listed for its
Internet address in the hostname database, /etc/hosts or
the Network Information Service (NIS).
– Network Information Service (NIS) is Sun
Microsystems' Yellow Pages (yp) client-server protocol
for distributing system configuration data such as user
and host names between computers on a network.
– You can find a host's canonical name using nslookup if
you say
set querytype=CNAME
DNS
• Address Record (A Record), assigns an IP address to a
domain name. When the domain name system was designed
it was recommended that no two A records refer to the same
IP address.
• Pointer Record. Also called a reverse record. A PTR record
associates an IP address with a canonical name.
– PTR records should point to a name that can be resolved back to the
IP address.
– The name of the pointer record is not the IP address itself, but is the
IP address’ four IP octets in reverse order followed by INADDR.ARPA.
– for Example:
192.168.0.1 becomes 1.0.168.192.IN-ADDR.ARPA.
Root Server
(princeton.edu, cit.princeton.edu, NS, IN)
(cit.princeton.edu, 128.196.128.233, A, IN)
(cisco.com, thumper.cisco.com, NS, IN)
(thumper.ciscoe.com, 128.96.32.20, A, IN)
…
Princeton Server
(cs.princeton.edu, optima.cs.princeton.edu, NS, IN)
(optima.cs.princeton.edu, 192.12.69.5, A, IN)
(ee.princeton.edu, helios.ee.princeton.edu, NS, IN)
(helios.ee.princeton.edu, 128.196.28.166, A, IN)
(jupiter.physics.princeton.edu, 128.196.4.1, A, IN)
(saturn.physics.princeton.edu, 128.196.4.2, A, IN)
(mars.physics.princeton.edu, 128.196.4.3, A, IN)
(venus.physics.princeton.edu, 128.196.4.4, A, IN)
CS Server
(cs.princeton.edu, optima.cs.princeton.edu, MX, IN)
(cheltenham.cs.princeton.edu, 192.12.69.60, A, IN)
(che.cs.princeton.edu, cheltenham.cs.princeton.edu,
CNAME, IN)
(optima.cs.princeton.edu, 192.12.69.5, A, IN)
(opt.cs.princeton.edu, optima.cs.princeton.edu,
CNAME, IN)
(baskerville.cs.princeton.edu, 192.12.69.35, A, IN)
(bas.cs.princeton.edu, baskerville.cs.princeton.edu,
CNAME, IN)
Name Resolution
• Strategies
Root
name
server
2
– forward
– iterative
– recursive
3
1
cicada.cs.princeton.edu
Client
192.12.69.60
8
4
Local
name
server
cicada.cs.princeton.edu Princeton
name
server
cs.princeton.edu, 192.12.69.5
5
• Local server
– need to know root at only one
place (not each host)
– site-wide cache
6
7
CS
name
server
Distributed File Systems
• Network File System (NFS)
– Provides transparent file access for client applications.
– Built on top of Sun RPC.
– NFS is used predominately with UDP. The NFS server
receives a clients request on port 2049.
– It is common to start multiple instances of the server
(nfsd).
Distributed File Systems
• No Transparency
Global AFS: /cs.princeton.edu/usr/llp/tmp/foo
Windows: f:/usr/llp/tmp/foo
• Transparency by Convention
– NFS: /usr/llp/tmp/foo
– Or Not: /n/fs/fac5/llp/tmp/foo
• Transparency by Architecture
– Sprite: /usr/llp/tmp/foo
• Private versus Shared
– ASF: /usr/llp/tmp/foo
versus /afs/shared
Applications
• File Transfer Protocol (FTP)
– FTP uses two TCP connections to transfer a file.
– The control connection is established on port number 21.
– The data connection is established through port 20.
• SMTP (Simple Mail Transfer Protocol) is a TCP/IP
protocol used in sending and receiving e-mail.
• The Hypertext Transfer Protocol (HTTP) is the set of rules
for exchanging files (text, graphic images, sound, video,
and other multimedia files) on the World Wide Web.
• Simple Network Management Protocol (SNMP) is the
protocol governing network management and the
monitoring of network devices and their functions.
RTP
• The Real-Time Transport Protocol (RTP) is an
Internet protocol standard that specifies a way for
programs to manage the real-time transmission of
multimedia data over either unicast or multicast
network services.
• RTP is commonly used in Internet telephony
applications. RTP does not in itself guarantee realtime delivery of multimedia data.
• RTP combines its data transport with a control
protocol (RTCP), which makes it possible to
monitor data delivery for large multicast networks.
Real-Time Transport Protocol (RTP)
• Monitoring allows the receiver to detect
– A sequence number is used to detect lost packets.
– A timestamp detects different delay jitter.
• Control Packets is sent periodically.
– Measure loss rate (fraction of packets received since
last report)
– measure jitter .
• RTP runs on top of the User Datagram Protocol
(UDP), although it can use other transport
protocols.
Session Control
• Video conferencing requires session control.
• The Session Initiation Protocol (SIP) is an Internet
Engineering Task Force (IETF) standard protocol for
initiating an interactive user session that involves
multimedia elements such as video, voice, chat, gaming,
and virtual reality.
– SIP can establish multimedia sessions or Internet telephony calls,
and modify, or terminate them.
– SIP uses RTP.
• H.323 is a standard built on top of RTP and approved by
the International Telecommunication Union (ITU) in 1996
to promote compatibility in videoconference transmissions
over IP networks.