&&' & + $, $ $ ( $" $ + ! " # $ " % Numeric addr. tough for humans to remember Numeric addr. impossible to guess

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1 Numeric addr. tough for humans to remember Numeric addr. impossible to guess Variable length (machines prefer fixed length) Potentially long! " # $ " % && & ( ( &( ) * & ( &( + $, $ $ ( $" $ $. -.

2 / && & ( ( &( ) * &( * &( + $, $ $ ( $" $ +!"#$ % & "( $ - && 0 $ - )* ( ( &( ) * &( * &) ( ( &( ) * &( * & ( ( &( ) * & ( & ( ( &( ) * & ( & ( ( &( ) * & ( &( ( ( &( ) * &( * &( ( ) &% & & ( ) &% & & ( ) &% &( &( ( ) &% &( & ( ) &% & &( Multi-homed: machine with more IP addresses (not necessarily routers)

3 #+ #,-." /01$/012 % % -. /23/$4/15$4/6/$4/64$4212 " )74*$4310$ ", )9 * :& ; <, = ; < >> " ; < & ( 1 ( 2 2 &&& 2 2 &&&

4 "9 9, 7 - abc.kkk.it differs from abc.kkk.de & $ ) * 97,, : ;

5 ? # < & & ==> && & && & ==> && & ),* # +, +,#"21,:# ), *" 5 / - &? * ( = / &

6 ? )* morgana.elet.polimi.it bianchi.it (bycicles.),9# IP addresses, Telephone numbers,... # # 3 4? A : && & B && & & & & ; ; " + A51 + =422

7 # - 1 =! " # $ $ $!#!! % $ )* )*B classificazione per tipologia Top level domain name Tipo di organizzazione COM Commerciali EDU Accademiche e didattiche GOV Statali MIL Militari NET Centri di Gestione di Internet ARPA ARPANET (obsoleto) INT Organizzazioni internazionali ORG Altre organizzazioni AERO industria trasporti aerei ASIA BIZ business CAT comunità catalana COOP Associazioni cooperative

8 # - &&& &&& & " % & " % ) & *! &!+ & " ( & " 999 registration authority italiana naming authority italiana /1 06/ ( # # # " && - && - && & && & & & &? + & & ) * &=- & ( C " & ( &# &

9 # ", -!"!,!,,,, $! $ & #" ", $! $ & & & ". - && & it unipa tti markov # C D $ C D & $ C D ), *,9 & & & & & &

10 E ;;F8-G,+ 9, H I,! 9! - B A B X.A Y.A Z.A J.B K.B L.B Zone Zone cut CAT.K.B DOG.K.B

11 E #? + &@5 7? + &@5? + &@5 7? + &@5 / ( $ : ; / $ - 7./ & 7, B? + &@5./ / & & 7 Authoritative server: provides original information for a zone ALWAYS capable to resolve name-ipaddr association

12 # -# ( - &=- & +# )#* 7 # & & A query should be resolved as fast as possible; It should be available 24 hours a day; It should be reachable via fast communication lines; It should be located in the centre of the network topology; It should be robust, without errors and interrupts..,$9# B

13 % % & & & # & 7? + &@5 && & # & & 7 D & & & && & -, $ B,)* 9H" J-. 4/64)88;#;8-;;. 8;#-(#8-F8-*

14 ) 9*? + &@5 & & && & #,,

15 # # gethostbyname(),) * :=9H >> # 8= " >>, /1/ /K2 /2 / Domain elet.polimi.it nameserver nameserver nameserver

16 )9 # H L* 4 5 6! && & $ ( ( &( ) * &( * &" $ ( ( &( ) * &( * &( * E. ;? E! : ;? :. ( ( &( ) * &( * &" : ; G -? :. * (local) Internet?# #,,#7 & H99$,

17 ?,, 9 $H 99 & 9 9," - $ A B C - $ B A C

18 # )9 L* (recursive + iterative approach).!! 7 8 % F -!! /!! 7 8!!! 7 8 $ :: & -! & & -!! Address is Address of ftp.elet.polimi.it? 9H$ HI $. - -» Updated list (13 root name servers as of aug 1997) at ftp://ftp.rs.internic.net/domain/named.root

19 # ) ) *!! 7 8 % F - & -!. Ask root server / ! & & -! Address of ftp.elet.polimi.it? # ) ) * F - & -! 3 8 $ ::! & & -! Address is Address of ftp.elet.polimi.it? timeout risk

20 Recursive server Authoritative server CACHE Performance improvements supplementary problems & complexity - H special domain in-addr.arpa used: to reverse lookup : direct lookup of in-addr.arpa Reverse domains form a hierarchical tree and are treated as any other Internet domain. Rfc2317 Classless In-ADDR.ARPA delegation

21 +.arpa.in-addr #7

22 - - # 2+ " ; 5 J 5 J A - / 5 F K ;9 &&

23 )* 9, ) * ) 6500A/#, $50A/,* 9 )*, 9#,#7? H % H % %9 basic types (many others practically unused): A ; A; < A 8= A 8A.;A# < A= - A

24 )*,--" L cerbero.elet.polimi.it IN A but try to look at the entry!! IN A IN A IN A =) <* A 4" - -,H )9 A * 8= " <0999 </0

25 8 9 = ,= <$.;$-.; < D && 7

26 ,,# ; D 4 ;! $ - ; ; allows to determine primary nameserver: it was not possible with an NS query B, unique worldwide 4 configuration parameters D

27 H 9 = few web interfaces around, most with extremely limited capabilities 9 H & A( + #7-0 &&& ;M8= )H N &, * elet.polimi.it origin = morgana.elet.polimi.it mail addr = root.morgana.elet.polimi.it serial = refresh = (3H) retry = 3600 (1H) expire = (1W) minimum ttl = (1D) elet.polimi.it nameserver = ns.polimi.it elet.polimi.it nameserver = fusberta.elet.polimi.it elet.polimi.it nameserver = venus.elet.polimi.it elet.polimi.it nameserver = morgana.elet.polimi.it ns.polimi.it internet address = fusberta.elet.polimi.it internet address = venus.elet.polimi.it internet address = morgana.elet.polimi.it internet address = unipa.it origin = sunipa.cuc.unipa.it mail addr = root.sunipa.cuc.unipa.it serial = refresh = (1D) retry = 7200 (2H) expire = (4w2d) minimum ttl = (2D) unipa.it nameserver = sunipa.cuc.unipa.it unipa.it nameserver = cucaix.cuc.unipa.it unipa.it nameserver = dns2.nic.it sunipa.cuc.unipa.it internet address = cucaix.cuc.unipa.it internet address = dns2.nic.it internet address =

28 8= " " % yahoo.it origin = ns0.corp.yahoo.com mail addr = hostmaster.yahoo-inc.com serial = refresh = 3600 (1H) retry = 1800 (30M) expire = (1W) minimum ttl = (6H) yahoo.it nameserver = ns.europe.yahoo.com yahoo.it nameserver = ns.yahoo.com yahoo.it nameserver = av1.yahoo.com ns.yahoo.com internet address = av1.yahoo.com internet address = yahoo.com origin = ns0.corp.yahoo.com mail addr = hostmaster.yahoo-inc.com serial = refresh = 1800 (30M) retry = 900 (15M) expire = (2W) minimum ttl = 9 (9S) yahoo.com nameserver = ns1.yahoo.com yahoo.com nameserver = ns3.europe.yahoo.com yahoo.com nameserver = ns5.dcx.yahoo.com ns1.yahoo.com internet address = ns3.europe.yahoo.com internet address = ns5.dcx.yahoo.com internet address = #. /4,=M, 16 bit fields 16 bit fields Identification No. Questions No. Authority RRs Questions (query) Answers Authoritative answers Additional information Flags No. RR answers No. Additional RR Same UDP packet up & down request response both

29 Set by client, returned unmodified by server (to match request with response).!-"!a0$- A/ "9 " )O2/4,* -#" -", "!% %-! " Name: domain name (or IP address) Query type (A=1, NS=2, MX=15, CNAME=12 ) Query class (1 for IN = Internet) - Domain Name Response type Class (IN) Time to live (in seconds) Length of resource data Resource data