COSC4377. Chapter 2: outline

Transcription

1 Lecture 7 Chapter 2: outline 2.1 principles of network applications app architectures app requirements 2.2 Web and HTTP 2.3 FTP 2.4 electronic mail SMTP, POP3, IMAP 2.5 DNS 2.6 P2P applications 2.7 socket programming with UDP and TCP 2 1

2 FTP: the file transfer protocol at host FTP interface FTP client local file system file transfer FTP remote file system transfer file to/from remote host client/ model client: side that initiates transfer (either to/from remote) : remote host ftp: RFC 959, October 1985, RFC 2228, June 1997, security ext., RFC 2428, September 1998, IPv6, ftp : control - port 21, data port 20 Slide derived from Kurose & Ross, 6 th Ed 3 FTP: separate control, data connections FTP client contacts FTP at port 21, using TCP client authorized over control connection client browses remote directory, sends commands over control connection when receives file transfer command, opens 2 nd TCP data connection (for file) to client after transferring one file, closes data connection FTP client TCP control connection, port 21 TCP data connection, port 20 FTP opens another TCP data connection to transfer another file control connection: out of band FTP maintains state : current directory, earlier authentication 4 2

3 FTP commands, responses sample commands: sent as ASCII text over control channel USER name PASS password LIST return list of file in current directory RETR filename retrieves (gets) file STOR filename stores (puts) file onto remote host sample return codes status code and phrase (as in HTTP) 331 Username OK, password required 125 data connection already open; transfer starting 425 Can t open data connection 452 Error writing file 5 FTP: Active and Passive modes Active FTP Client initiates connection to port 21 using a client port N>1023 for control and port N+1 for data Server using port 21 responds to client port N Client sends command PORT N+1 to FTP using port 20 initiates data connection to client's data port N+1 FTP client sends ACKs to 's port 20 Passive FTP (to avoid firewall, NAT, and related issues, e.g. used by Web browsers) Client initiates connection to port 21 using a client port N>1023 for control and port N+1 for data Server using port 21 responds to client port N Client sends command PASV to the Server creates a port P>1023 and informs client to connect to P for data transfer Client using port N+1 initiates connection to port P Server using port P sends ACK to client port N+1 Reference:

4 File Transfer Protocols using UDP Examples: SABUL (Simple Available Bandwidth Utilization Library) pdf RBUDP (Reliable Blast UDP) FOBS (Fast Object Based File Transfer System) Three concurrent SABUL streams, each with 1 Gbps theoretical peak pdf SABUL, Chicago Amsterdam, RTT 110ms 7 GridFTP: The Protocol A high performance, secure, reliable data transfer protocol optimized for high bandwidth wide area networks FTP with well defined extensions Uses basic Grid security Multiple data channels for parallel transfers Partial file transfers Third party transfers Reusable data channels Command pipelining GGF recommendation GFD.20 April July 2003 Current version, 5.5.4, stable/gridftp/ Tutorial, 8 4

5 Control and Data Channels GridFTP (and FTP) use (at least) two separate socket connections: A control channel for carrying the commands and responses A data Channel for actually moving the data Control Channel and Data Channel can be (optionally) completely separate processes. Typical Installation Control Data Separate Processes Control Data Striped Server Control Data 9 Parallel Data Streams Multiple TCP streams between sender and receiver Sender pushes multiple blocks in parallel streams Blocks reassembled at receiving side and put into correct order Protection against dropped packets for each stream Parallel Transfer Fully utilizes bandwidth of network interface on single nodes 10 5

6 Striped GridFTP Service Multiple nodes work together as a single logical GridFTP Every node of the cluster is used to transfer data into/out of the cluster Each node reads/writes only pieces they re responsible for Head node coordinates transfers Multiple levels of parallelism CPU, bus, NIC, disk etc. Maximizes use of Gbit+ WANs Parallel Filesystem Parallel Filesystem Striped Transfer Fully utilizes bandwidth of Gb+ WAN using multiple nodes. 11 Source: Bill Alcock, GlobusWorld

7 GridFTP % Globus code No licensing issues 2000 Stable, extensible 0 IPv6 Support XIO for different transports Striping multi Gb/sec wide area transport Pluggable Front end: e.g., future WS control channel Back end: e.g., HPSS, cluster file systems Transfer: e.g., UDP, NetBLT transport WS = Web Services, HPSS = High Performance Storage System NetBLT = Network Block Transfer, RFC 998, March 1987 Bandwidth (Mbps) Disk-to-disk on TeraGrid p g Degree of Striping # Stream = 1 # Stream = 2 # Stream = 4 # Stream = 8 # Stream = 16 # Stream = TCP buffer size control GridFTP Features Tune buffers to latency of network Regular FTP optimized for low latency networks, not tunable Dramatic improvements for high latency WAN transfers 90% of network utilization possible 27 GB/s achieved with commodity hardware 14 7

8 GridFTP Integrated instrumentation: Developers can use client API and plug in mechanism to leverage different instrumentation Performance markers Restart markers Throughput performance Netlogger style performance tracking 15 Extensive Logging in the Server Multiple log levels: ERROR, WARN, INFO, DUMP, ALL Log to stdio, syslog, file, Log all connections/transfers to single file or unique files Netlogger style logging Control permissions on log files 16 8

9 GridFTP Features Data Storage Interface (DSI) Interfaces to various storage types Implement simple functions such as send, receive, mkdir, DSI modules available for HPSS and SRB Globus FTP client library (API): Integration of data transport capabilities directly into applications Plug in architecture for installing fault recovery and performance tuning algorithms Asynchronous programming model 17 GridFTP: Client API Simple client flow comprises: 1. Setup transfer details including number of parallel data channels, TCP buffer size, local buffer number and size 2. Open connection to URL and provide a completion callback function to be called when transfer complete 3. Setup local buffers to hold read/write 4. Register data callback function to be called for filling/flushing buffers 5. Set not done flag 6. Loop/wait until completion callback clears not done flag Work is done inside the data callback function Local buffer filled with data (receiver) & ready to be flushed Receive the offset into the file and any error code fseek() to the correct place and fwrite() to file Register another empty buffer/callback combination 18 9

10 GridFTP: Tool Mechanics Server mechanics globus-gridftp- Usually runs as root Usually run as a daemon; connections fork new process and setuid Can run inetd/xinetd if so desired Port 2811 is standard but is configurable Logging and security highly configurable Client mechanics globus-url-copy Options for parallel channels, TCP buffer size, data buffer size, debugging, recursive directory transfers, etc. 19 GridFTP: Secure, High Performance Data Transport Server side computation Extended retrieve (ERET), Extended store (ESTO) Simple pre processing (partial get, sub sampling ) Can greatly reduce network load Client must also support ESTO/ERET functionality 20 10

11 Chapter 2: outline 2.1 principles of network applications app architectures app requirements 2.2 Web and HTTP 2.3 FTP 2.4 electronic mail SMTP, POP3, IMAP 2.5 DNS 2.6 P2P applications 2.7 socket programming with UDP and TCP 21 e mail and Messaging Statistics e mail 2.2 billion s 247 billion s are sent each day content/uploads/2012/04/ Statistics Report Brochure.pdf Key Global Telecom Indicators for the World (estimates) Over-the-Top (OTT) messaging v SMS messaging. OTT messages SMS MMS messages messages ,492 billion 7,844 billion 207 billion ,846 billion 8,600 billion 228 billion ,293 billion 9,554 billion 277 billion Sources: Portio Research Febuary 2012 Global millions Per 100 people Mobile cellular subscriptions 5, Fixed telephone lines 1, Active mobile broadband subscriptions 1, Fixed broadband subscriptions Source: International Telecommunication Union (November 2011) via: mobi Thinking marketing tools/latest mobilestats/c#mobilemessaging 22 11

12 Electronic mail Three major components: s mail s simple mail transfer protocol: SMTP User Agent a.k.a. mail reader composing, editing, reading mail messages e.g., Outlook, Thunderbird, iphone mail client outgoing, incoming messages stored on mail SMTP mail SMTP SMTP outgoing message queue mail mailbox 23 Electronic mail: mail s mail s: mailbox contains incoming messages for message queue of outgoing (to be sent) mail messages SMTP protocol between mail s to send messages client: sending mail : receiving mail mail SMTP mail SMTP SMTP mail 24 12

13 Electronic Mail: SMTP [RFC 2821] uses TCP to reliably transfer message from client to, port 25 direct transfer: sending to receiving three phases of transfer handshaking (greeting) transfer of messages closure command/response interaction (like HTTP, FTP) commands: ASCII text response: status code and phrase messages must be in 7 bit ASCI 25 Scenario: Alice sends message to Bob 1) Alice uses UA to compose message to bob@someschool.edu 2) Alice s UA sends message to her mail ; message placed in message queue 3) client side of SMTP opens TCP connection with Bob s mail 4) SMTP client sends Alice s message over the TCP connection 5) Bob s mail places the message in Bob s mailbox 6) Bob invokes his to read message 1 mail 2 3 Alice s mail 4 mail 5 Bob s mail

14 Sample SMTP interaction S: 220 hamburger.edu C: HELO crepes.fr S: 250 Hello crepes.fr, pleased to meet you C: MAIL FROM: S: 250 Sender ok C: RCPT TO: S: 250 Recipient ok C: DATA S: 354 Enter mail, end with "." on a line by itself C: Do you like ketchup? C: How about pickles? C:. S: 250 Message accepted for delivery C: QUIT S: 221 hamburger.edu closing connection 27 SMTP: final words SMTP uses persistent connections SMTP requires message (header & body) to be in 7 bit ASCII SMTP uses CRLF.CRLF to determine end of message comparison with HTTP: HTTP: pull SMTP: push both have ASCII command/response interaction, status codes HTTP: each object encapsulated in its own response msg SMTP: multiple objects sent in multipart msg 28 14

15 Mail message format SMTP: protocol for exchanging msgs RFC 822: standard for text message format: header lines, e.g., To: From: Subject: different from SMTP MAIL FROM, RCPT TO: commands! Body: the message ASCII characters only header body blank line 29 Mail access protocols SMTP SMTP mail access protocol (e.g., POP, IMAP) sender s mail receiver s mail SMTP: delivery/storage to receiver s mail access protocol: retrieval from POP: Post Office Protocol [RFC 1939]: authorization, download IMAP: Internet Mail Access Protocol [RFC 1730]: more features, including manipulation of stored msgs on HTTP: gmail, Hotmail, Yahoo! Mail, etc

16 authorization phase client commands: : declare name pass: password responses +OK -ERR transaction phase, client: list: list message numbers retr: retrieve message by number dele: delete quit POP3 protocol S: +OK POP3 ready C: bob S: +OK C: pass hungry S: +OK successfully logged on C: list S: S: S:. C: retr 1 S: <message 1 contents> S:. C: dele 1 C: retr 2 S: <message 1 contents> S:. C: dele 2 C: quit S: +OK POP3 signing off 31 POP3 (more) and IMAP more about POP3 previous example uses POP3 download and delete mode Bob cannot re read e mail if he changes client POP3 download andkeep : copies of messages on different clients POP3 is stateless across sessions IMAP keeps all messages in one place: at allows to organize messages in folders keeps state across sessions: names of folders and mappings between message IDs and folder name 32 16

17 Extra material on SMTP ESMTP (Extended SMTP; RFC 1869, 1995) allows 8 bit data transmission; use EHLO (extended Hello) to replace HELO Authentication process in FTP, POP3, and IMAP is not encrypted. Use FTP/SSL, POP3S, or IMAPS if possible. Multipart MIME (Multi part Internet Mail Extension) From: "Senders Name" <sender@sendersdomain.com> To: "Recipient Name" <somerecipient@recipientdomain.com> Message ID: <5bec11c119194c @sendersdomain.com> Date: Sat, 24 Sep :06: Subject: Sample Multi Part MIME Version: 1.0 Content Type: multipart/alternative; boundary=" =_NextPart_DC7E1BB5_1105_4DB3_BAE3 =_NextPart_DC7E1BB5_1105_4DB3_BAE3 Content type: text/plain; charset=iso Content Transfer Encoding: quoted printable Sample Text Content =_NextPart_DC7E1BB5_1105_4DB3_BAE3 Content type: text/html; charset=iso Content Transfer Encoding: quoted printable <html><head></head> <body>sample HTML Content</body></html> =_NextPart_DC7E1BB5_1105_4DB3_BAE Another Example Binary encoded Attachment Part 1 Part 2 From: <donald.duck@disney.com> CRLF To: <mickey.mouse@disney.com> CRLF Subject: foobar CRLF MIME Version: 1.0 CRLF Content Type: multipart/mixed; CRLF boundary= "KkK170891tpbkKk FV_KKKkkkjjwq" CRLF CRLF KkK170891tpbkKk FV_KKKkkkjjwq CRLF Content Type: text/plain; charset=us ASCII CRLF CRLF here goes the text message CRLF CRLF KkK170891tpbkKk FV_KKKkkkjjwq CRLF Content Type: application/octet stream CRLF Content Transfer Encoding: base64 CRLF Content Disposition: attachment; CRLF filename= "suggested name of the attachment" CRLF CRLF here goes the Base64 encoded attachment CRLF KkK170891tpbkKk FV_KKKkkkjjwq CRLF CRLF.CRLF Blank line Blank line Blank line Blank line 34 17

18 Chapter 2: outline 2.1 principles of network applications app architectures app requirements 2.2 Web and HTTP 2.3 FTP 2.4 electronic mail SMTP, POP3, IMAP 2.5 DNS 2.6 P2P applications 2.7 socket programming with UDP and TCP 35 DNS: domain name system people: many identifiers: SSN, name, passport # Internet hosts, routers: IP address (32 bit) used for addressing datagrams name, e.g., used by humans Q: how to map between IP address and name, and vice versa? Domain Name System: distributed database implemented in hierarchy of many name s application layer protocol: hosts, name s communicate to resolve names (address/name translation) note: core Internet function, implemented as applicationlayer protocol complexity at network s edge 36 18

19 DNS services DNS: services, structure hostname to IP address translation host aliasing canonical, alias names mail aliasing load distribution replicated Web s: many IP addresses correspond to one name why not centralize DNS? single point of failure traffic volume distant centralized database maintenance A: doesn t scale! 37 Domain Names Statistics TLD Total Domains COM 102,764,716 NET 14,160,747 ORG 9,832,140 INFO 5, BIZ 2,327,124 TOTAL 134,797,932 9/16/ Q Number of TLDs 86.9 million Number of country code top level domains (.CN,.UK,.DE, etc.). 220 million Number of registered domain names in numbers/ As of October 2009 there were 21 generic TLDs and 250 country domains (based on ISO 3166 country abbreviations) Domain names managed by IANA, the Internet Assigned Numbers Authority,

20 DNS: a distributed, hierarchical database Root DNS Servers com DNS s org DNS s edu DNS s yahoo.com DNS s amazon.com DNS s pbs.org DNS s poly.edu umass.edu DNS sdns s client wants IP for 1 st approx: client queries root to find.com DNS client queries.com DNS to get amazon.com DNS client queries amazon.com DNS to get IP address for 39 DNS: root name s contacted by local name that can not resolve name root name : contacts authoritative name if name mapping not known gets mapping returns mapping to local name e. NASA Mt View, CA f. Internet Software C. Palo Alto, CA (and 48 other sites) c. Cogent, Herndon, VA (5 other sites) d. U Maryland College Park, MD h. ARL Aberdeen, MD j. Verisign, Dulles VA (69 other sites ) a. Verisign, Los Angeles CA (5 other sites) b. USC-ISI Marina del Rey, CA l. ICANN Los Angeles, CA (41 other sites) g. US DoD Columbus, OH (5 other sites) k. RIPE London (17 other sites) i. Netnod, Stockholm (37 other sites) m. WIDE Tokyo (5 other sites) 13 root name s worldwide 40 20

21 DNS Root Servers 377 s as of s.org/ 41 Server Operator Locations A VeriSign, Inc. Sites: 6 Global: 6 Local: 0 Los Angeles, CA, US; New York, NY, US *; Frankfurt, DE *; Hong Kong, HK; Palo Alto, CA, US *; Ashburn, VA, US * B Information Sciences Institute Sites: 1 Global: 0 Local: 1 Earth C Cogent Communications Sites: 6 Global: 6 Local: 0 Herndon, VA, US; Los Angeles, CA, US; New York, NY, US; Chicago, IL, US; Frankfurt, DE; Madrid, ES D University of Maryland Sites: 1 Global: 1 Local: 0 College Park, MD, US * E NASA Ames Research Center Sites: 12 Global: 1 Local: 11 Mountain View, CA, US; Sydney, AU; Cape Town, ZA; Tokyo, JP; Brussels, BE; London, UK; San Paulo, BR; Atlanta, GA, US; Chicago, IL, US; New York, NY, US; Seattle, WA, US; Los Angeles, CA, US F Internet Systems Consortium, Inc. Sites: 49 Global: 2 Local: 47 Ottawa, Canada *; Palo Alto, CA, US *; San Jose, CA, US; New York, NY, US *; San Francisco, CA, US *; Madrid, ES; Hong Kong, HK; Los Angeles, CA, US *; Rome, Italy; Auckland, NZ *; Sao Paulo, BR; Beijing, CN; Seoul, KR *; Moscow, RU *; Taipei, TW; Dubai, AE; Paris, FR *; Singapore, SG; Brisbane, AU *; Toronto, CA *; Monterrey, MX; Lisbon, PT *; Johannesburg, ZA; Tel Aviv, IL; Jakarta, ID; Munich, DE *; Osaka, JP *; Prague, CZ *; Amsterdam, NL *; Barcelona, ES *; Nairobi, KE; Chennai, IN; London, UK *; Santiago de Chile, CL; Dhaka, BD; Karachi, PK; Torino, IT; Chicago, IL, US *; Buenos Aires, AR; Caracas, VE; Oslo, NO *; Panama, PA; Quito, EC; Kuala Lumpur, Malaysia *; Suva, Fiji; Cairo, Egypt; Atlanta, GA, US; Podgorica, ME; St. Maarten, AN * G Sites: 6 Global: 6 Local: 0 U.S. DOD Network Information Center Columbus, OH, US; San Antonio, TX, US; Honolulu, HI, US; Fussa, JP; Stuttgart Vaihingen, DE; Naples, IT H U.S. Army Research Lab Sites: 2 Global: 2 Local: 0 Aberdeen Proving Ground, MD, US *; San Diego, CA, US * I Netnod (formerly Autonomica) Sites: 43 Stockholm, SE *; Helsinki, FI; Milan, IT *; London, UK *; Geneva, CH *; Amsterdam, NL (2 sites) *; Oslo, NO *; Bangkok, TH *; Hong Kong, HK *; Brussels, BE *; Frankfurt, DE *; Ankara, TR *; Bucharest, RO *; Chicago, IL, US; Washington, DC, US; Tokyo, JP (2 sites) *; Kuala Lumpur, MY *; Palo Alto, CA, US *; Jakarta, ID; Wellington, NZ; Johannesburg, ZA *; Perth, AU *; Singapore, SG; Miami, FL, US; Mumbai, IN; Beijing, CN; Manila, PH; Doha, QA *; Colombo, LK *; Vienna, AT *; Paris, FR *; Taipei, TW *; Porto Alegre, BR; Yerevan, AM *; Thimphu, BT *; Manama, BH; Karachi, PK; Tallinn, EE *; Kiev, UA *; Ulaanbaatar, MN *; Lulea, SE J VeriSign, Inc. Sites: 70 Global: 63 Local: 5 Dulles, VA, US (2 sites); Dulles, VA, US (1 sites); Ashburn, VA, US *; Miami, FL, US; Atlanta, GA, US; Seattle, WA, US; Chicago, IL, US; New York, NY, US *; Honolulu, HI, US; Mountain View, CA, US (1 sites); Mountain View, CA, US (1 sites); San Francisco, CA, US (2 sites) *; Dallas, TX, US; Amsterdam, NL; London, UK; Stockholm, SE (2 sites); Tokyo, JP; Seoul, KR; Beijing, CN; Singapore, SG; Dublin, IE; Kaunas, LT; Nairobi, KE; Montreal, CA; Perth, AU; Sydney, AU; Cairo, EG; Cairo, EG; Warsaw, PL (2 sites); Brasilia, BR; Sao Paulo, BR; Sofia, BG; Prague, CZ; Johannesburg, ZA; Toronto, CA; Buenos Aires, AR; Madrid, ES; Fribourg, CH; Hong Kong, HK (2 sites); Turin, IT; Mumbai, IN; Oslo, NO; Brussels, BE; Paris, FR (2 sites); Helsinki, FI; Frankfurt, DE *; Riga, LV; Milan, IT; Rome, IT; Lisbon, PT; San Juan, PR; Edinburgh, UK; Tallinn, EE; Taipei, TW; New York, NY, US *; Palo Alto, CA, US *; Anchorage, US; Moscow, RU; Manila, PH; Kuala Lumpur, MY; Luxembourg City, LU; Guam, GU, US; Vancouver, CA; Wellington, NZ s.org/ 42 21

22 Server Operator Locations K RIPE NCC Sites: 18 Global: 5 Local: 13 London, UK *; Amsterdam, NL *; Frankfurt, DE *; Athens, GR *; Doha, QA; Milan, IT *; Reykjavik, IS *; Helsinki, FI *; Geneva, CH *; Poznan, PL *; Budapest, HU *; Abu Dhabi, AE; Tokyo, JP *; Brisbane, AU *; Miami, FL, US *; Delhi, IN; Novosibirsk, RU; Dar es Salaam, TZ L ICANN Sites: 120 Ezeiza, Argentina *; Mascot, Australia (2 sites) *; Brisbane, Queensland, Australia *; Perth, Western Australia, Australia (2 sites) *; Vienna, Austria *; Al Muharraq, Bahrain *; Dhaka, Bangladesh *; Brussels, Belgium (2 sites) *; Rio de Janeiro, Brazil *; Salvador, Bahia, Brazil *; Fortaleza, Ceara, Brazil *; Sao Jose dos Campos, Brazil *; Sao Paulo, Brazil *; Brasilia, Distrito Federal, Brazil *; Belo Horizonte, Minas Gerais, Brazil *; Londrina, Parana, Brazil *; Curitiba, Parana, Brazil *; Porto Alegre, Rio Grande do Sul, Brazil *; Florianopolis, Santa Catarina, Brazil *; Campinas, Sao Paulo State, Brazil *; Sofia, Bulgaria *; Mississauga, Ontario, Canada (2 sites) *; Ottawa, Ontario, Canada (2 sites) *; Toronto, Ontario, Canada *; Santiago, Chile *; Concepcion, Biobio Region, Chile *; Bogota, Colombia *; Prague, Czech Republic *; Copenhagen, Denmark *; Quito, Ecuador *; Cairo, Egypt *; Lyon, France *; Marseille, France *; Paris, France *; Paris Orly, Paris, France *; St Denis, Reunion, France *; Berlin, Germany *; Hamburg, Germany *; Munich, Bavaria, Germany *; Dortmund, North Rhine Westphalia, Germany *; Dusseldorf, North Rhine Westphalia, Germany *; Heraklion, Crete, Greece *; Hagatna, Guam *; Jakarta, Java, Indonesia *; Dublin, Ireland *; Turin, Italy *; Narita, Japan *; Tokyo, Honshu, Japan *; Semey, Kazakhstan *; Nairobi, Kenya *; Luxembourg Findel, Luxembourg *; Monterrey, Nuevo Leon, Mexico *; Maputo, Mozambique *; Kathmandu, Nepal *; Haarlemmermeer, Netherlands *; Christchurch, New Zealand *; Mangere, New Zealand (2 sites) *; Wellington, New Zealand *; Ullensaker, Norway *; Beijing, Peoples Republic of China (2 sites) *; Callao, Peru *; Metro Manila, Philippines *; Warsaw, Poland *; Moscow, Russia *; Dammam, Saudi Arabia *; Jeddah, Saudi Arabia *; Riyadh, Saudi Arabia *; Dakar, Senegal *; Changi, Singapore *; Cape Town, South Africa (2 sites) *; Johannesburg, Gauteng, South Africa *; Incheon, South Korea *; El Prat de Llobregat, Spain *; Malmo, Sweden *; Stockholm, Sweden *; Geneva, Switzerland *; Zurich, Switzerland *; Istanbul, Turkey (3 sites) *; Kharkiv, Ukraine *; Kiev, Ukraine *; Odessa, Ukraine *; Saginaw Bay, Alaska, United States *; Burbank, California, United States *; Los Angeles, California, United States (2 sites) *; San Jose, California, United States *; San Jose, Costa Rica *; Santa Ana, California, United States *; Denver, Colorado, United States *; Jacksonville, Florida, United States *; Melbourne, Florida, United States *; Miami, Florida, United States (2 sites) *; Atlanta, Georgia, United States (2 sites) *; Honolulu, Hawaii, United States *; Chicago, Illinois, United States *; Boston, Massachusetts, United States (2 sites) *; New York City, New York, United States *; Portland, Oregon, United States *; Philadelphia, Pennsylvania, United States *; Culpeper, Virginia, United States *; SeaTac, Washington, United States *; Montevideo, Uruguay *; Sanaa, Yemen *; Vancouver, Canada *; Leeds, United Kingdom *; Anchorage, Alaska, United States *; Porto, Portugal * M WIDE Project Sites: 6 Global: 5 Local: 1 Tokyo, JP (3 sites) *; Seoul, KR; Paris, FR *; San Francisco, CA, US * s.org/ 43 DNS Root Server K 44 22

23 TLD, authoritative s top level domain (TLD) s: responsible for com, org, net, edu, aero, jobs, museums, and all top level country domains, e.g.: uk, fr, ca, jp Network Solutions maintains s for.com TLD Educause for.edu TLD authoritative DNS s: organization s own DNS (s), providing authoritative hostname to IP mappings for organization s named hosts can be maintained by organization or service provider 45 Local DNS name does not strictly belong to hierarchy each ISP (residential ISP, company, university) has one also called default name when host makes DNS query, query is sent to its local DNS has local cache of recent name to address translation pairs (but may be out of date!) acts as proxy, forwards query into hierarchy 46 23

24 DNS name resolution example root DNS host at cis.poly.edu wants IP address for gaia.cs.umass.edu iterated query: contacted replies with name of to contact I don t know this name, but ask this local DNS dns.poly.edu requesting host cis.poly.edu TLD DNS 6 authoritative DNS dns.cs.umass.edu gaia.cs.umass.edu 47 DNS name resolution example root DNS recursive query: puts burden of name resolution on contacted name heavy load at upper levels of hierarchy? local DNS dns.poly.edu TLD DNS requesting host cis.poly.edu authoritative DNS dns.cs.umass.edu gaia.cs.umass.edu 48 24

25 DNS: caching, updating records once (any) name learns mapping, it caches mapping cache entries timeout (disappear) after some time (TTL) TLD s typically cached in local name s thus root name s not often visited cached entries may be out of date (best effort name to address translation!) if name host changes IP address, may not be known Internet wide until all TTLs expire update/notify mechanisms proposed IETF standard RFC Some statistics for the K DNS Root 9/25/2012 Global s.org/ (18 nodes, 5 global, 13 local) 50 25

26 DNS Root I 43 sites 51 DNS Root Server I load 9/25/2012 'Daily' graph (5 Minute Average) stats/sums/all.html 52 26

27 DNS Root Server I load 9/18 9/ 'Weekly' graph (30 Minute Average) stats/sums/all.html 53 DNS Root Server I load 2 years ending 9/25/12 'Two year' graph (1 Day Average) stats/sums/all.html 54 27