Il routing dei datagram IP si basa su un semplice algoritmo di scelta del router successivo (next hop) che ciascun router esegue sui pacchetti ricevuti e non destinati ad esso stesso.
La scelta del router successivo viene fatta in base all'indirizzo di destinazione del pacchetto e di una tabella di routing mantenuta sul router.
Questa tabella è essenzialmente formata da una serie di entrate, ciascuna delle quali associa l'indirizzo di una rete all'indirizzo di un router adiacente cui vanno inviati tutti i pacchetti destinati a quella rete.
La tabella può contenere anche indirizzi di singoli host e righe di default.
Ciascun router ripete questo algoritmo finche` il pacchetto non arriva alla rete di destinazione.
Routing tables Destination Gateway Flags Refcnt Use Interface default 195.32.0.254 UG 2 4089933 ln0 127.0.0.1 127.0.0.1 UH 1 0 lo0 195.32 195.32.0.2 U 62 14121145 ln0 195.32.1.89 195.32.0.250 UGHDM 0 38686 ln0 195.32.1.161 195.32.0.250 UGHDM 0 2838 ln0 195.32.1.193 195.32.0.198 UGHD 0 48 ln0 195.32.2.6 195.32.0.250 UGHDM 0 85976 ln0 195.32.2.22 195.32.0.250 UGHDM 0 3639 ln0 195.32.2.25 195.32.0.250 UGHDM 0 11177 ln0 195.32.2.37 195.32.0.250 UGHDM 0 19269 ln0 195.32.2.89 195.32.0.248 UGHDM 0 26308 ln0 195.32.2.100 195.32.0.248 UGHD 1 39 ln0 195.32.2.119 195.32.0.33 UGHD 0 47 ln0 195.32.2.170 195.32.0.250 UGHDM 1 133 ln0 195.32.2.181 195.32.0.250 UGHDM 0 2395 ln0 195.32.2.182 195.32.0.250 UGHDM 0 40408 ln0 195.32.2.218 195.32.0.248 UGHDM 0 5169 ln0 195.32.3.3 195.32.0.250 UGHDM 0 7858 ln0 195.32.3.23 195.32.0.250 UGHD 0 5775 ln0 195.32.3.52 195.32.0.248 UGHDM 0 1113 ln0 195.32.3.53 195.32.0.250 UGHDM 0 51428 ln0 195.32.3.79 195.32.0.248 UGHDM 0 10154 ln0 195.32.3.115 195.32.0.248 UGHDM 0 11503 ln0 195.32.3.132 195.32.0.248 UGHD 0 4 ln0 195.32.3.150 195.32.0.250 UGHDM 0 19055 ln0 195.32.4.2 195.32.0.248 UGHD 0 124 ln0 195.32.4.3 195.32.0.250 UGHDM 0 12879 ln0 195.32.4.22 195.32.0.198 UGHD 0 29 ln0 195.32.4.62 195.32.0.248 UGHDM 0 4388 ln0 195.32.4.94 195.32.0.198 UGHD 0 182 ln0 195.32.4.125 195.32.0.198 UGHDM 0 2748 ln0 195.32.4.131 195.32.0.247 UGHD 0 15567 ln0 195.32.4.161 195.32.0.248 UGHDM 0 7421 ln0 195.32.4.254 195.32.0.250 UGHDM 0 30058 ln0 195.32.5.15 195.32.0.248 UGHDM 0 1544 ln0 195.32.5.39 195.32.0.250 UGHD 0 1537 ln0 195.32.5.43 195.32.0.250 UGHDM 0 570 ln0 195.32.5.58 195.32.0.248 UGHDM 0 4182 ln0 195.32.5.80 195.32.0.250 UGHDM 0 13498 ln0 195.32.5.83 195.32.0.250 UGHDM 0 1822 ln0 195.32.5.88 195.32.0.250 UGHDM 0 701 ln0 195.32.6 195.32.0.253 UGDM 0 5966 ln0 195.32.7 195.32.0.247 UGD 0 219 ln0 195.32.9.2 195.32.0.197 UGHD 0 1716 ln0 195.32.9.18 195.32.0.197 UGHD 0 1178 ln0 195.250.224.15 195.32.0.251 UGHD 0 12 ln0 195.250.224.16 195.32.0.251 UGHD 0 17 ln0 195.250.224.18 195.32.0.251 UGHD 0 16 ln0 195.250.224.23 195.32.0.251 UGHD 0 31 ln0 195.250.224.24 195.32.0.251 UGHD 0 53 ln0 195.250.224.26 195.32.0.251 UGHD 0 26 ln0 195.250.224.27 195.32.0.251 UGHD 0 14 ln0 195.250.224.28 195.32.0.251 UGHD 0 25 ln0 195.250.224.30 195.32.0.251 UGHD 0 47 ln0 195.250.224.130 195.32.0.251 UGHD 0 344 ln0 195.250.224.194 195.32.0.253 UGHD 0 363 ln0 195.250.225.65 195.32.0.250 UGHDM 0 3144 ln0 195.250.230.191 195.32.0.248 UGHD 0 39 ln0 195.250.230.215 195.32.0.250 UGHD 0 11 ln0
traceroute www.mit.edu traceroute to DANDELION-PATCH.MIT.EDU (18.181.0.31), 30 hops max, 40 byte packets 1 garisenda (195.32.0.254) 3 ms 3 ms 2 ms 2 sansiro-s0-0 (195.250.255.206) 27 ms 45 ms 34 ms 3 Serial3-7.GW1.MLN2.ALTER.NET (146.188.33.85) 42 ms 72 ms 66 ms 4 Serial3-7.GW1.MLN2.ALTER.NET (146.188.33.85) 90 ms 41 ms 30 ms 5 Fddi0-0.CR1.MLN2.Alter.Net (146.188.31.33) 63 ms 31 ms 94 ms 6 217.Hssi5-0.CR1.LND2.Alter.Net (146.188.3.33) 768 ms 99 ms 107 ms 7 311.Atm1-0.BR2.LND2.Alter.Net (146.188.3.106) 78 ms 100 ms 148 ms 8 215.ATM4-0-0.CR2.TCO1.Alter.Net (137.39.103.86) 171 ms 167 ms 170 ms 9 316.ATM4-0-0.BR1.TCO1.Alter.Net (137.39.74.74) 177 ms 158 ms 202 ms 10 137.39.23.14 (137.39.23.14) 171 ms 158 ms 161 ms 11 cambridge1-br1.bbnplanet.net (4.0.5.42) 167 ms 174 ms 253 ms 12 cambridge2-br2.bbnplanet.net (4.0.1.202) 255 ms 203 ms 175 ms 13 ihtfp.mit.edu (192.233.33.3) 234 ms 174 ms 194 ms 14 W20-RTR-FDDI.MIT.EDU (18.168.0.8) 237 ms 205 ms 263 ms 15 DANDELION-PATCH.MIT.EDU (18.181.0.31) 185 ms * 213 ms
ping www.cs.unibo.it PING leporello.cs.unibo.it (130.136.2.254): 56 data bytes 64 bytes from 130.136.2.254: icmp_seq=0 ttl=244 time=260 ms 64 bytes from 130.136.2.254: icmp_seq=1 ttl=244 time=144 ms 64 bytes from 130.136.2.254: icmp_seq=2 ttl=244 time=265 ms 64 bytes from 130.136.2.254: icmp_seq=3 ttl=244 time=196 ms 64 bytes from 130.136.2.254: icmp_seq=4 ttl=244 time=308 ms 64 bytes from 130.136.2.254: icmp_seq=5 ttl=244 time=175 ms 64 bytes from 130.136.2.254: icmp_seq=6 ttl=244 time=218 ms 64 bytes from 130.136.2.254: icmp_seq=7 ttl=244 time=186 ms 64 bytes from 130.136.2.254: icmp_seq=8 ttl=244 time=192 ms 64 bytes from 130.136.2.254: icmp_seq=9 ttl=244 time=530 ms ----leporello.cs.unibo.it PING Statistics---- 10 packets transmitted, 10 packets received, 0% packet loss round-trip (ms) min/avg/max = 144/247/530 msSOFTWARE PROGETTO DSNET