dns: domain name system people: many identifiers: – ssn, name, passport # internet hosts, routers:...
TRANSCRIPT
![Page 1: DNS: Domain Name System People: many identifiers: – SSN, name, Passport # Internet hosts, routers: – IP address (32 bit) - used for addressing datagrams](https://reader030.vdocuments.site/reader030/viewer/2022032707/56649e565503460f94b4e102/html5/thumbnails/1.jpg)
DNS: Domain Name System
People: many identifiers:– SSN, name, Passport #
Internet hosts, routers:– IP address (32 bit) - used for
addressing datagrams– “name”, e.g.,
hermite.cs.smith.edu - used by humans
Q: map between IP addresses and name ?
Domain Name System:• distributed database implemented
in hierarchy of many name servers• application-layer protocol host,
routers, name servers to communicate to resolve names (address/name translation)– note: core Internet function
implemented as application-layer protocol
– complexity at network’s “edge”
![Page 2: DNS: Domain Name System People: many identifiers: – SSN, name, Passport # Internet hosts, routers: – IP address (32 bit) - used for addressing datagrams](https://reader030.vdocuments.site/reader030/viewer/2022032707/56649e565503460f94b4e102/html5/thumbnails/2.jpg)
DNS
DNS services• Hostname to IP address
translation• Host aliasing
– Canonical and alias names
• Mail server aliasing• Load distribution
– Replicated Web servers: set of IP addresses for one canonical name
Why not centralize DNS?• single point of failure• traffic volume• distant centralized database• maintenance
doesn’t scale!
![Page 3: DNS: Domain Name System People: many identifiers: – SSN, name, Passport # Internet hosts, routers: – IP address (32 bit) - used for addressing datagrams](https://reader030.vdocuments.site/reader030/viewer/2022032707/56649e565503460f94b4e102/html5/thumbnails/3.jpg)
Structure of DNS Names• Each name consists of a sequence of alphanumeric
components separated by periods • Examples:
– www.ssuet.edu.pk– ssuet.edu.pk– khi.comsats.net.pk– aurangzeb.ssuet.edu.pk
• Names are hierarchical, with most-significant component on the right
• Left-most component is, generally, a computer name
![Page 4: DNS: Domain Name System People: many identifiers: – SSN, name, Passport # Internet hosts, routers: – IP address (32 bit) - used for addressing datagrams](https://reader030.vdocuments.site/reader030/viewer/2022032707/56649e565503460f94b4e102/html5/thumbnails/4.jpg)
Structure of DNS Names• Top Level Domains (right-most
components; also known as TLDs) are defined by global authority Organizations apply for names in a top-level domain: – fsu.edu– macdonalds.com
• Organizations determine own internal structure – eng.fsu.edu– cs.purdue.edu
![Page 5: DNS: Domain Name System People: many identifiers: – SSN, name, Passport # Internet hosts, routers: – IP address (32 bit) - used for addressing datagrams](https://reader030.vdocuments.site/reader030/viewer/2022032707/56649e565503460f94b4e102/html5/thumbnails/5.jpg)
Distributed, Hierarchical Database
Client wants IP for www.amazon.com; 1st approx:• Client queries a root server to find com DNS server• Client queries com DNS server to get amazon.com DNS
server• Client queries amazon.com DNS server to get IP address
for www.amazon.com
Root DNS Servers
com DNS servers org DNS servers edu DNS servers
poly.eduDNS servers
umass.eduDNS servers
yahoo.comDNS servers
amazon.comDNS servers
pbs.orgDNS servers
![Page 6: DNS: Domain Name System People: many identifiers: – SSN, name, Passport # Internet hosts, routers: – IP address (32 bit) - used for addressing datagrams](https://reader030.vdocuments.site/reader030/viewer/2022032707/56649e565503460f94b4e102/html5/thumbnails/6.jpg)
DNS: Root name servers• contacted by local name server that can not resolve name• root name server:
– contacts authoritative name server if name mapping not known– gets mapping– returns mapping to local name server
13 root name servers
worldwideb USC-ISI Marina del Rey, CAl ICANN Los Angeles, CA
e NASA Mt View, CAf Internet Software C. Palo Alto,
CA (and 17 other locations)
i Autonomica, Stockholm (plus 3 other locations)
k RIPE London (also Amsterdam, Frankfurt)
m WIDE Tokyo
a Verisign, Dulles, VAc Cogent, Herndon, VA (also Los Angeles)
d U Maryland College Park, MDg US DoD Vienna, VAh ARL Aberdeen, MD
j Verisign, ( 11 locations)
![Page 7: DNS: Domain Name System People: many identifiers: – SSN, name, Passport # Internet hosts, routers: – IP address (32 bit) - used for addressing datagrams](https://reader030.vdocuments.site/reader030/viewer/2022032707/56649e565503460f94b4e102/html5/thumbnails/7.jpg)
TLD and Authoritative Servers• Top-level domain (TLD) servers: responsible for com, org,
net, edu, etc, and all top-level country domains uk, fr, ca, jp.– Network solutions maintains servers for com TLD
• Authoritative DNS servers: organization’s DNS servers, providing authoritative hostname to IP mappings for organization’s servers (e.g., Web and mail).– Can be maintained by organization or service provider
• Local DNS servers: organization’s DNS servers located on various subnets to provide DNS lookups for hosts on the subnet. May not be accessible from outside the subnet. Their IP addresses are part of the host's network configuration (manual or DHCP).
![Page 8: DNS: Domain Name System People: many identifiers: – SSN, name, Passport # Internet hosts, routers: – IP address (32 bit) - used for addressing datagrams](https://reader030.vdocuments.site/reader030/viewer/2022032707/56649e565503460f94b4e102/html5/thumbnails/8.jpg)
Local Name Server
• Does not strictly belong to hierarchy• Each ISP (residential ISP, company, university)
has one.– Also called “default name server”
• When a host makes a DNS query, query is sent to its local DNS server– Acts as a proxy, forwards query into hierarchy.
![Page 9: DNS: Domain Name System People: many identifiers: – SSN, name, Passport # Internet hosts, routers: – IP address (32 bit) - used for addressing datagrams](https://reader030.vdocuments.site/reader030/viewer/2022032707/56649e565503460f94b4e102/html5/thumbnails/9.jpg)
![Page 10: DNS: Domain Name System People: many identifiers: – SSN, name, Passport # Internet hosts, routers: – IP address (32 bit) - used for addressing datagrams](https://reader030.vdocuments.site/reader030/viewer/2022032707/56649e565503460f94b4e102/html5/thumbnails/10.jpg)
Inverse domainCountry domains
![Page 11: DNS: Domain Name System People: many identifiers: – SSN, name, Passport # Internet hosts, routers: – IP address (32 bit) - used for addressing datagrams](https://reader030.vdocuments.site/reader030/viewer/2022032707/56649e565503460f94b4e102/html5/thumbnails/11.jpg)
DNS Name Resolution Example
![Page 12: DNS: Domain Name System People: many identifiers: – SSN, name, Passport # Internet hosts, routers: – IP address (32 bit) - used for addressing datagrams](https://reader030.vdocuments.site/reader030/viewer/2022032707/56649e565503460f94b4e102/html5/thumbnails/12.jpg)
DNS Name Resolution Example
![Page 13: DNS: Domain Name System People: many identifiers: – SSN, name, Passport # Internet hosts, routers: – IP address (32 bit) - used for addressing datagrams](https://reader030.vdocuments.site/reader030/viewer/2022032707/56649e565503460f94b4e102/html5/thumbnails/13.jpg)
DNS Operation
![Page 14: DNS: Domain Name System People: many identifiers: – SSN, name, Passport # Internet hosts, routers: – IP address (32 bit) - used for addressing datagrams](https://reader030.vdocuments.site/reader030/viewer/2022032707/56649e565503460f94b4e102/html5/thumbnails/14.jpg)
DNS: caching and updating records
• once (any) name server learns a mapping, it caches the mapping (Domain’s DNS = IP) – cache entries timeout (disappear) after some time
(usually 20 minutes)– TLD servers typically cached longer in local name
servers• Thus root name servers not often visited
• update/notify mechanisms under design by IETF– RFC 2136– http://www.ietf.org/html.charters/dnsind-charter.html
![Page 15: DNS: Domain Name System People: many identifiers: – SSN, name, Passport # Internet hosts, routers: – IP address (32 bit) - used for addressing datagrams](https://reader030.vdocuments.site/reader030/viewer/2022032707/56649e565503460f94b4e102/html5/thumbnails/15.jpg)
DNS recordsDNS: distributed db storing resource records (RR)
• Type=NS– name is domain (e.g. foo.com)– value is IP address of
authoritative name server for this domain
RR format: (name, value, type,ttl)
Type=A name is hostname value is IP address
Type=CNAME name is an alias name
for some “canonical” (the real) name
value is canonical name
Type=MX value is hostname of
mailserver associated with name
![Page 16: DNS: Domain Name System People: many identifiers: – SSN, name, Passport # Internet hosts, routers: – IP address (32 bit) - used for addressing datagrams](https://reader030.vdocuments.site/reader030/viewer/2022032707/56649e565503460f94b4e102/html5/thumbnails/16.jpg)
DNS protocol, messagesDNS protocol : query and reply messages, both with same message format
msg header identification: 16 bit #
for query, reply to query uses same #
flags: query or reply recursion desired recursion available reply is authoritative
![Page 17: DNS: Domain Name System People: many identifiers: – SSN, name, Passport # Internet hosts, routers: – IP address (32 bit) - used for addressing datagrams](https://reader030.vdocuments.site/reader030/viewer/2022032707/56649e565503460f94b4e102/html5/thumbnails/17.jpg)
DNS protocol, messages
Name, type fields for a query
RRs in reponseto query
records forauthoritative servers
additional “helpful”info that may be used
![Page 18: DNS: Domain Name System People: many identifiers: – SSN, name, Passport # Internet hosts, routers: – IP address (32 bit) - used for addressing datagrams](https://reader030.vdocuments.site/reader030/viewer/2022032707/56649e565503460f94b4e102/html5/thumbnails/18.jpg)
wireshark Display of DNS Response
ID is random nonceused to authenticateResponse to Query
18
![Page 19: DNS: Domain Name System People: many identifiers: – SSN, name, Passport # Internet hosts, routers: – IP address (32 bit) - used for addressing datagrams](https://reader030.vdocuments.site/reader030/viewer/2022032707/56649e565503460f94b4e102/html5/thumbnails/19.jpg)
Pure P2P architecture
• no always-on server• • arbitrary end systems
directly• communicate• • peers are intermittently• connected and change IP• addresses
![Page 20: DNS: Domain Name System People: many identifiers: – SSN, name, Passport # Internet hosts, routers: – IP address (32 bit) - used for addressing datagrams](https://reader030.vdocuments.site/reader030/viewer/2022032707/56649e565503460f94b4e102/html5/thumbnails/20.jpg)
File Distribution: Server-Client vs P2P
![Page 21: DNS: Domain Name System People: many identifiers: – SSN, name, Passport # Internet hosts, routers: – IP address (32 bit) - used for addressing datagrams](https://reader030.vdocuments.site/reader030/viewer/2022032707/56649e565503460f94b4e102/html5/thumbnails/21.jpg)
BitTorrent Overview
• Website allowing peers to share music, video and other media files• Central server helps users find initial set of peers that have pieces of
the file• Tracker server keeps track of peers possessing content of individual
files• Users download the file by participating in exchange:
– They exchange pieces that they have– for pieces that they don’t have
• Therefore, for the system to work, users must have incentive to give• Users who just get, but do not give are called free riders• Protocol must discourage free riding
![Page 22: DNS: Domain Name System People: many identifiers: – SSN, name, Passport # Internet hosts, routers: – IP address (32 bit) - used for addressing datagrams](https://reader030.vdocuments.site/reader030/viewer/2022032707/56649e565503460f94b4e102/html5/thumbnails/22.jpg)
BitTorrent
![Page 23: DNS: Domain Name System People: many identifiers: – SSN, name, Passport # Internet hosts, routers: – IP address (32 bit) - used for addressing datagrams](https://reader030.vdocuments.site/reader030/viewer/2022032707/56649e565503460f94b4e102/html5/thumbnails/23.jpg)
BitTorrent
![Page 24: DNS: Domain Name System People: many identifiers: – SSN, name, Passport # Internet hosts, routers: – IP address (32 bit) - used for addressing datagrams](https://reader030.vdocuments.site/reader030/viewer/2022032707/56649e565503460f94b4e102/html5/thumbnails/24.jpg)
BitTorrent
![Page 25: DNS: Domain Name System People: many identifiers: – SSN, name, Passport # Internet hosts, routers: – IP address (32 bit) - used for addressing datagrams](https://reader030.vdocuments.site/reader030/viewer/2022032707/56649e565503460f94b4e102/html5/thumbnails/25.jpg)
BitTorrent
![Page 26: DNS: Domain Name System People: many identifiers: – SSN, name, Passport # Internet hosts, routers: – IP address (32 bit) - used for addressing datagrams](https://reader030.vdocuments.site/reader030/viewer/2022032707/56649e565503460f94b4e102/html5/thumbnails/26.jpg)
P2P: Searching for Information
![Page 27: DNS: Domain Name System People: many identifiers: – SSN, name, Passport # Internet hosts, routers: – IP address (32 bit) - used for addressing datagrams](https://reader030.vdocuments.site/reader030/viewer/2022032707/56649e565503460f94b4e102/html5/thumbnails/27.jpg)
P2P: centralized directory
![Page 28: DNS: Domain Name System People: many identifiers: – SSN, name, Passport # Internet hosts, routers: – IP address (32 bit) - used for addressing datagrams](https://reader030.vdocuments.site/reader030/viewer/2022032707/56649e565503460f94b4e102/html5/thumbnails/28.jpg)
P2P: problems with centralized directory
• Single point of failure• Performance bottleneck• Copyright infringement: “target” of lawsuit is obvious
file transfer is decentralized, but locating content is highly decentralized
![Page 29: DNS: Domain Name System People: many identifiers: – SSN, name, Passport # Internet hosts, routers: – IP address (32 bit) - used for addressing datagrams](https://reader030.vdocuments.site/reader030/viewer/2022032707/56649e565503460f94b4e102/html5/thumbnails/29.jpg)
P2P: decentralized directory
• Each peer is either a group leader or assigned to a group leader.
• Group leader tracks the content in all its children.
• Peer queries group leader; group leader may query other group leaders.
ordinary peer
group-leader peer
neighoring re la tionshipsin overlay network
![Page 30: DNS: Domain Name System People: many identifiers: – SSN, name, Passport # Internet hosts, routers: – IP address (32 bit) - used for addressing datagrams](https://reader030.vdocuments.site/reader030/viewer/2022032707/56649e565503460f94b4e102/html5/thumbnails/30.jpg)
Decentralized Indexing: Query Flooding
![Page 31: DNS: Domain Name System People: many identifiers: – SSN, name, Passport # Internet hosts, routers: – IP address (32 bit) - used for addressing datagrams](https://reader030.vdocuments.site/reader030/viewer/2022032707/56649e565503460f94b4e102/html5/thumbnails/31.jpg)
Query Flooding
![Page 32: DNS: Domain Name System People: many identifiers: – SSN, name, Passport # Internet hosts, routers: – IP address (32 bit) - used for addressing datagrams](https://reader030.vdocuments.site/reader030/viewer/2022032707/56649e565503460f94b4e102/html5/thumbnails/32.jpg)
Skype• IP telephony system• Allows users to make phone calls
– to Skype users– to regular phone users
• Calls are routed via Skype nodes• Central login server• Super-nodes
– Nodes that know about location of other nodes
![Page 33: DNS: Domain Name System People: many identifiers: – SSN, name, Passport # Internet hosts, routers: – IP address (32 bit) - used for addressing datagrams](https://reader030.vdocuments.site/reader030/viewer/2022032707/56649e565503460f94b4e102/html5/thumbnails/33.jpg)
![Page 34: DNS: Domain Name System People: many identifiers: – SSN, name, Passport # Internet hosts, routers: – IP address (32 bit) - used for addressing datagrams](https://reader030.vdocuments.site/reader030/viewer/2022032707/56649e565503460f94b4e102/html5/thumbnails/34.jpg)
Skype P2P Network
• Super-nodes are nodes with powerful CPU and network bandwidth
• One has to qualify to become a super-node
• Super-nodes know about locations of other nodes
• Ordinary nodes contact super-nodes to place calls
![Page 35: DNS: Domain Name System People: many identifiers: – SSN, name, Passport # Internet hosts, routers: – IP address (32 bit) - used for addressing datagrams](https://reader030.vdocuments.site/reader030/viewer/2022032707/56649e565503460f94b4e102/html5/thumbnails/35.jpg)
Skype Components
• Skype client – the client program used to make phone calls• Host cache – list of other known Skype users, maintained at
each Skype client• Skype login server – a centralized component. Processes
account information, authentication
![Page 36: DNS: Domain Name System People: many identifiers: – SSN, name, Passport # Internet hosts, routers: – IP address (32 bit) - used for addressing datagrams](https://reader030.vdocuments.site/reader030/viewer/2022032707/56649e565503460f94b4e102/html5/thumbnails/36.jpg)
Skype User Search Procedure
• A Skype client making a phone call needs to find other users• It contacts super-nodes from its host cache, asking them to help
find the user• Super-nodes return a list of nodes to contact• The client contacts those nodes• If unsuccessful, the client asks for more nodes• Guarantees to find any user that has logged in within the last 72
hours• Not much specific information on Skype protocol is available…