UDP ????????????????

1
UDP ????????????????

• 2002/07/19
• miyu

2
introduction

• UDP(User Datagram Protocol)
• ?????????????
• ?????????
• ?????? ??????????????
• IP???????????
• ???? RFC768

3
UDP??????
IP??????
UDP??????
IP??? 20bytes
UDP??? 8bytes
UDP???
4
?????

• ???????????????
• IP????????????????????????????????

15
16
31
0
16???????????
16??????????
8bytes
16???UDP????
16???UDP??????
???
5
UDP?????????

• UDP????UDP???????????????
• ???8byte
• (0byte?????UDP???????????OK)
• (???????????)?(IP????)UDP????

16???????????
16??????????
8bytes
16???UDP????
16???UDP??????
???
6
UDP??????

• UDP???????????
• IP???????????IP?????
• UDP????????????
• ?????????????
• ???????????????????

16???????????
16??????????
8bytes
16???UDP????
16???UDP??????
???
7
UDP???????????????
(12byte)
?????2? ?????????
??????? ?????
???????(0)
8
UDP???????????

• 16????????????
• (IP???????????????)
• ?????????????
• 8?????
• ?????????????
• ???????
• UDP?????
• 20????IP???
• ??IP???????
• IP?????????UDP???????

9
tcpdump???
Checksum? ???

• ???tcpdump
• UDP??????????

UDP??????? ???????
1 0.0 sun.1900 gt
gemini.echoudp 9(UDP cksum6e90) 2 0.303755
(0.30389) gemini.echo gt sun.1900udp 9(UDP
cksum0) 3 17.392480(17.0887) sun.1904
gtaix.echoudp 9(UDP cksum6e3b) 4
17.614371(0.2219) aix.echo gtsun.1904udp 9(UDP
cksum6e3b) 5 32.092454(14.4781) sun.1907 gt
solaris.echoudp 9(UDP cksum6e74) 6.32.314378(0.2
219) solaris.echo gt sun.1907udp 9(UDP
cksum6e74)
16bit????????????????
10
??????????????

• ?????NFS????40???
• ?????????????????????????
• ARP?Ethernet?????????????Ethernet?????IP??????????
  ?????
• ICMP?IP???????????IP???????TCPorUDP?????????
• TCP???UDP??????????
• ????UDP????????????????????
• TCP?????????????????????????
• UDP?TCP?????????????????????
• ???????????????

11
UDP?????????

• ????????????????????????????
• ?????????????
• ???????
• ??????????????????
• ?????????????????????????
• ?????????
• ?????10245000

12
IP Fragmentation

• Physical network??????????????????
• ??????????MTU(Maximum Transmit Unit)????
• ??????????
• ?????????????
• ????????????????????
• ?????????????????????????????
• ?????????????????????IP??????
• ???IP???????????

13
(??)IP???

• IP????????????
• ???????????????????????

• ???????????????????

4??? ?????
16?????(???)
8???TOS
4??? ????
16??????
13??????????????
??? ???
20???
8????????
16????????????
8???????(TTL)
32??????IP????

• ????????????????????
• ????????????

????????????????
32?????IP????
?????(??)
???
14
???????????

• ??????? ?????????
• ????IP???????????
• ????????????
• ??????????
• ????????????????????????
• IP????????????????????
• TCP???????????TCP??????????
• UDP??????

15
???????????tcpdump

• 1 0.0 bsdi.1112 gt svr4.discard udp 1471
• 2 21.008303(21.0083) bsdi.1114 gt srv4.discard
  udp 1472
• 3 50.449704(29.4414) bsdi.1116gt svr4.discard
  udp1473
• (frag 26304 1480_at_0)
• 4 50.450040(0.0003)bsdi gt svr4(frag263041_at_1480)
• 5 75.328650(24.8786) bsdi.1118gtsvr4.discard udp
  1474
• (frag 263131480_at_0)
• 6 75.328982(0.0003) bsdi gt svr4 (frag
  263132_at_1480)

16
????????????

• ethernet????????????1500???
• ?????????????1472???

IP??????
IP??? 20bytes
UDP??? 8bytes
UDP???(1473bytes)
IP??? 20bytes
UDP??? 8bytes
UDP???(1473bytes)
IP??? 20bytes
1byte
???? 1
???? 2
17
ICMP Unreachable Error(Fragmentation Required)

• ????????????????
• ????????????????????????????
• ???????????????????
• ICMP??????
• ?????????MTU??????
• ??MTU???????????

18
ICMP Unreachable Error
????????MTU????(???????0)
???(3)
??????
???(3)
8???
???(0)
????????MTU
IP???(????????) ?????IP??????????8???
19
Traceroute???MTU????????!

• ????????????MTU?????????????????????
• ??traceroute???
• ???????????????????????
• ??????????????MTU?
• ICMP Unreachable Error???????
• ??????????????

20
Traceroute?????MTU??

• traceroute.pmtu slip
• Traceroute to slip(140.252.13.65),30 hops max
• Outgoing MTU1500
• 1 bsdi(140.252.13.35) 53ms 6ms 6ms
• 2 bsdi (140.252.13.35) 6ms
• Fragmentation required DF set, next hop MTU 296
• 2 slip (140.252.13.65) 377ms 378ms 377ms

21
UDP?????MTU??????

• ???????????????????????????????????????
• MTU?????????????????????????
• DF???(?????????)?????
• ?????????????????
• ???ICMP??????MTU????????????????????????
• 30???????DF??????????
• MTU????????

22
UDP?????MTU??????
???tcpdump???
MTU1500
MTU1500
MTU1500
MTU1500
bsdi
netb
slip
sun
solaris
SLIP
SLIP
MTU296
MTU296
MTU1500
MTU552
DF?????????650byte?UDP??????
ICMP Cant fragment error
23
??MTU?????? tcpdump

• 1. 0.0 solaris.38196gt slip.discardudp 650(DF)
• 2. 0.04199(0.0042)bsdigtsolarisicmp
• slip unreachable need to frag mtu 296(DF)
• 3. 4.950193(4.9460) solaris.38196gtslip.discardudp
  650(DF)
• 4. 4.954325(0.0041) bsdigtsolarisicmp
• slip unreachable need to frag mtu 296(DF)
• 5. 9.779855(4.8255) solaris.37974gtslip.discardudp
  650(frag 35278272_at_0)
• 6. 9.930018(0.1502)solarisgtslip (frag
  35278272_at_272)
• 7. 9.990170(0.0602) solarisgtslip (frag
  35278114_at_544)

24
Interaction Between UDP and ARP

• ARP??????????UDP?????????
• ?????????????????ARP request?ARP reply????????
• ????????????????ARP request???
• ARP????1????1 request???????????
• ??????????????????????
• ??????????????

25
Interaction Between UDP and ARP

• ???ARP reply??5???
• ICMPtime exceeded during reassemblyerror
• ????????..????????
• ????????????????????????
• Timeout?????????????
• ??????????????????????
• ?????0?????????????????
• ???????????????????????????

26
UDP?????????????

• ?????65535????IP??????????
• IP???????(16???)??
• UDP?65535 20(IP header) 8(UDP header)
  65507???
• ?????????????
• ????????????????????????????(8192?????)
• TCP/IP???????????
• IP???????576????????
• ??????????????
• ????????

27
ICMP Source Quench Error

• UDP???????????????????

28
ICMP Source Quench Error

• ????????
• ????????
• ??UDP????????????????????
• TCP?????????????
• ????????????
• ?????????????????????
• UDP???????
• End-to-End??????????

29
UDP??????

• ????IP?????????????????
• ???????????????
• ?????????????????????????????
• destination IP address??????UDP??????????
• ????????????????????????
• ?????????????????????
• ???????queing?????????
• ICMP Source Quench Error ??????????????
• FIFO(??????)

30
UDP??????

• ????IP???????
• ????????
• ?????????????????????IP?????1??????????????IP????
  ?????????????
• ??????????IP???????
• ???IP????UDP??????1??????
• ??????????

31
???

• UDP?????????
• IP?????????????????????????
• IP??????????
• ICMP???????
• UDP?ARP?????
• ICMP????????