12. Name & Address 최양희서울대학교컴퓨터공학부

Transcription

1 12. Name & Address 최양희서울대학교컴퓨터공학부

2 How do you get IP address? Manual Configuration Stateful Address Configuration (i.e. from servers) BOOTP DHCPv4, DHCPv6 Stateless Autoconfiguration : IPv Yanghee Choi 2

3 Address Resolution RARP Hardware address ---> IP address requires direct access to the network hardware waste in reply frame (only IP address info is present) do not support dynamically assigned hardware address local broadcast is used - unable to extend beyond router BOOTP (Bootstrap Protocol) UDP, limited broadcast IP address, server hostname, boot filename etc. DHCP (Dynamic Host Configuration Protocol) dynamic IP address assignment extension to BOOTP 2009 Yanghee Choi 3

4 BOOTP Discover one s own IP address, server host address, filename to be loaded Carried over IP/UDP - application program Never fragmented RFC Yanghee Choi 4

5 Protocol Overview A single packet exchange Client broadcasts bootrequest packet contains client s hardware address, IP address (if known), generic filename (ex. Unix), vendor-specific filename, server name (optional) Server answers with bootreply packet limited broadcast contains client IP address, boot filename (fullpath), vendor specific filename 2009 Yanghee Choi 5

6 Why Broadcast? client server BOOTrequest?? ARPrequest If BOOTreply is unicast using client IP address, then the server first sends ARPrequest to get client s hardware address. But the client does not have yet its IP address, and cannot respond Yanghee Choi 6

7 Retransmission Policy Binary Backoff (max. 60 sec.) Random delay - to avoid collisions after power-up UDP checksum Don t Fragment Bit 2009 Yanghee Choi 7

8 DHCPv4 Provides configuration parameters to hosts Protocol for host-specific configuration parameters from a DHCP server to a host Mechanism for allocation of network addresses to hosts Based on BOOTP Client - Server over UDP (server : port 67, client : port 68) works beyond router Added automatic allocation of reusable network addresses and additional configuration options (In BOOTP, manual configuration was used) RFC 2131 (March 1997) 2009 Yanghee Choi 8

9 IP IP Address Subnet Mask TTL MTU Default Router Static Router TCP TTL Configuration Parameters Examples KeepAlive interval 2009 Yanghee Choi 9

10 DHCPv4 IP Address Allocation Manual allocation - same as BOOTP Automatic allocation - a permanent address is assigned automatically by the network to the newly attached hosts Dynamic allocation - lease address for a limited period of time 2009 Yanghee Choi 10

11 DHCPv4 Overview Server (not selected) Client Begins initialization Server (selected) Determines configuration DHCPDISCOVER DHCPOFFER DHCPDISCOVER DHCPOFFER Determines configuration Collects replies Selects configuration DHCPREQUEST DHCPREQUEST Commits configuration DHCPACK Initialization complete Graceful shutdown 2009 Yanghee Choi DHCPRELEASE Discards lease 11

12 Address Reuse Server (not selected) Client Begins initialization Server (selected) Locates configuration DHCPREQUEST DHCPREQUEST DHCPACK Initialization complete DHCPACK Locates configuration (subsequent DHCPACKs ignored) 2009 Yanghee Choi 12

13 DHCP State Diagram (client) INIT/REBOOT INIT DHCPACK/ record lease, set T1,T2 /DHCPREQUEST DHCPNAK/Restart REBOOTING DHCPOFFER/ Discard DHCPOFFER, DHCPACK DHCPNAK/ discard DHCPNAK/Discard offer DHCPACK/DHCPDECLINE /DHCPREQUEST REQUESTING DHCPACK/ record lease, set T1,T2 BOUND /DHCPDISCOVER SELECTING DHCPOFFER/ DHCPNAK, Lease expired/ halt network DHCPACK/ record lease, set T1,T2 REBINDIND T2 expires/ broadcast DHCPREQUEST DHCPNAK/ halt network DHCPACK/ record lease, T1 expires/ set T1,T2 DHCPREQUEST to 2009 Yanghee Choi leasing server RENEWING 13

14 Client Timers T1 T2 At time T1, the client sends DHCPREQUEST to the server (unicast) to extend its lease Default value = 0.5 X duration_of_lease At time T2, the client sends DHCPREQUEST to any server (broadcast) to extend its lease Default value = X duration_of_lease 2009 Yanghee Choi 14

15 IPv6 auto-configuration Stateless - nodes configure addresses themselves with information from routers (if available); no managed addresses Stateful - nodes use DHCPv6 to obtain addresses and more These are not mutually exclusive Duplicate address detection (DAD) used to avoid duplicated use of the same address Link-local address always available All_DHCP_Relay_Agents_and_Servers (FF02::1:2) All_DHCP_Servers (FF05::1:3) A node always creates a link-local address (stateless) Allows for direct communication between nodes on a link DHCPv6 client therefore has an address it can use 2009 Yanghee Choi 15

16 DHCPv6 RFC 3315 Changes from DHCPv4 Configuration of dynamic updates to DNS Address deprecation for dynamic renumbering Authentication Clients can ask for multiple IP addresses Addresses can be reclaimed Integration between stateful and stateless autoconfiguration 2009 Yanghee Choi 16

17 DHCPv6 Operation 2009 Yanghee Choi 17

18 DHCPv6 Msg 2009 Yanghee Choi 18

19 Stateless Autoconfiguration Interface ID automatically derived IEEE addresses use MAC-to-EUI-64 conversion Other addresses use other means, such as random number generation Host creates a link-local address Host performs duplicate address check Host sends RS to the all-routers multicast address (ff01::2) Router unicasts RA with prefix information Host adds prefix to Interface ID to form global unicast address 2009 Yanghee Choi 19

20 Stateless : Link Local Address 2009 Yanghee Choi 20

21 Obtaining Network Prefix RS Router Solicitation RA Router Advertisement NS Neighbor Solicitation NA Neighbor Advertisement 2009 Yanghee Choi 21

22 Duplicate Address Detection Must be performed by all nodes Performed with both stateless and stateful autoconfiguration Performed before assigning a unicast address to an interface Performed on interface initialization Not performed for anycast addresses Link must be multicast capable New address is called "tentative" as long as duplicate address detection takes place 2009 Yanghee Choi 22

23 DAD Operation 1.Interface joins all-nodes multicast group 2.Interface joins solicited-node multicast group 3.Node sends one NS with Target address = tentative IP address Source address = unspecified (::) Destination address = tentative solicited-node address If address already exists, the particular node sends a NA with Target address = tentative IP address Destination address = tentative solicited-node address If soliciting node receives NA with target address set to the tentative IP address, the address must be duplicate 2009 Yanghee Choi 23

24 How do routers get network prefix? RFC 3633 Using DHCPv Yanghee Choi 24

25 Dynamic DNS Service DNS service for dynamic IP address For servers with dynamic IP addresses Third party commercial service Updates DNS entry when new address is assigned 2009 Yanghee Choi 25

26 DNS Translation from high-level names to IP addresses etc. RFC 1034, 1035 Hierarchical Names delegation of authority independent of physical connection 2009 Yanghee Choi 26

27 DNS name space is partitioned authority of each subset is delegated to designated agents Domain Name consists of labels separated by period ( mmlab.snu.ac.kr ) Top-level country code domains us, kr, jp, fr.. Top-level generic domains.aero,.asia,.biz,.cat,.com,.coop,.edu,.gov,.info,.jobs,.mobi,.int,.mil,.museum,.name,.net,.org,.pro,.tel and.travel Second-level domains (Korea) : co, ac, go, re, pe, ne 2009 Yanghee Choi 27

28 Domain Name Mapping server software - Name Server client software - Name Resolver Root Server server for Korea kr server for com com server for France fr server for academia ac.kr server for SNU snu.ac.kr 2009 Yanghee Choi 28

29 Domain Name Resolution resolver server server query (name, type...) recursive resolution resolved answer (address...) contact other server resolved answer (address...) resolved answer (address...) iterative resolution refer other server query (name, type...) resolved answer (address...) 2009 Yanghee Choi 29 resolved answer (address...)

30 Name Resolution Client should know at least one name server Server should know at least one name server of upper level (parent) 2009 Yanghee Choi 30

31 Caching name caching at each host/server to save cost fast response works in case of other servers failures indicate nonauthorative binding, when information is retrieved from the local cache authorative response include TTL value for the binding hosts can copy local server s database extremely fast response protection against the local server s failure 2009 Yanghee Choi 31

32 DNS Resource Record Types TYPE MEANING CONTENTS A Host Address 32-bit IP address CNAME Canonical Name Canonical domain name for an alias HINFO CPU & OS Name of CPU and OS MINFO Mailbox Info Info about a mailbox or mail list MX Mail Exchanger 16-bit preference and name of host that acts as mail exchanger for domain NS Name Server Name of authorative server for domain PTR Pointer Domain Name SOA Start of Authority Multiple fields that specify which parts of the naming hierarchy a server implements TXT Arbitrary text Uninterpreted string of ASCII text 2009 Yanghee Choi 32

33 Pointer Query client IP address (in literal string, type = PTR) server domain name 2009 Yanghee Choi 33

34 Further Issues Addresses for Ubiquitous World Multihoming Anonymity Attack on the DNS root servers 인터넷대란 Slammer Worm on MS SQL server Infected 8800 servers in 10 minutes 2009 Yanghee Choi 34