최양희서울대학교컴퓨터공학부
Manual Configuration Stateful Address Configuration (i.e. from servers) BOOTP DHCPv4, DHCPv6 Stateless Autoconfiguration : IPv6 2005 Yanghee Choi 2
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 2005 Yanghee Choi 3
Discover one s own IP address, server host address, filename to be loaded Carried over IP/UDP - application program Never fragmented RFC1542 2005 Yanghee Choi 4
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 2005 Yanghee Choi 5
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.. 2005 Yanghee Choi 6
Binary Backoff (max. 60 sec.) Random delay - to avoid collisions after power-up UDP checksum Don t Fragment Bit 2005 Yanghee Choi 7
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) 2005 Yanghee Choi 8
Examples IP IP Address Subnet Mask TTL MTU Default Router Static Router TCP TTL KeepAlive interval 2005 Yanghee Choi 9
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 2005 Yanghee Choi 10
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 DHCPRELEASE Discards lease 2005 Yanghee Choi 11
Server (not selected) Client Begins initialization Server (selected) Locates configuration DHCPREQUEST DHCPREQUEST DHCPACK Initialization complete DHCPACK Locates configuration (subsequent DHCPACKs ignored) 2005 Yanghee Choi 12
INIT/REBOOT INIT DHCPACK/ record lease, set T1,T2 /DHCPREQUEST DHCPNAK/Restart REBOOTING DHCPOFFER/ Discard DHCPNAK/Discard offer DHCPACK/DHCPDECLINE REQUESTING DHCPOFFER, DHCPACK DHCPNAK/ discard /DHCPREQUEST DHCPACK/ record lease, set T1,T2 BOUND /DHCPDISCOVER SELECTING DHCPNAK, Lease expired/ halt network DHCPACK/ record lease, set T1,T2 DHCPOFFER/ REBINDIND T2 expires/ broadcast DHCPREQUEST DHCPNAK/ halt network DHCPACK/ record lease, T1 expires/ set T1,T2 DHCPREQUEST to 2005 Yanghee Choi leasing server RENEWING 13
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 = 0.875 X duration_of_lease 2005 Yanghee Choi 14
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 2005 Yanghee Choi 15
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 2005 Yanghee Choi 16
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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 2005 Yanghee Choi 19
Stateless : Link Local Address 2005 Yanghee Choi 20
RS Router Solicitation RA Router Advertisement NS Neighbor Solicitation NA Neighbor Advertisement 2005 Yanghee Choi 21
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 2005 Yanghee Choi 22
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 2005 Yanghee Choi 23
How do routers get network prefix? RFC 3633 Using DHCPv6 2005 Yanghee Choi 24
DNS service for dynamic IP address For servers with dynamic IP addresses Third party commercial service Updates DNS entry when new address is assigned 2005 Yanghee Choi 25
Translation from high-level names to IP addresses etc. RFC 1034, 1035 Hierarchical Names delegation of authority independent of physical connection 2005 Yanghee Choi 26
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 ) com, edu, gov, mil, net, org (USA) country code (us, kr, jp, fr..) biz, info, name, museum, coop, aero, pro, int & more co, ac, go, nm, re (Korea) 2005 Yanghee Choi 27
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 2005 Yanghee Choi 28
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...) 2005 Yanghee Choi 29 resolved answer (address...)
Client should know at least one name server Server should know at least one name server of upper level (parent) 2005 Yanghee Choi 30
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 2005 Yanghee Choi 31
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 2005 Yanghee Choi 32
client IP address (in literal string, type = PTR) server domain name 2005 Yanghee Choi 33
Addresses for Ubiquitous World Multihoming Anonymity Attack on the DNS root servers 2003.1.25 인터넷대란 Slammer Worm on MS SQL server Infected 8800 servers in 10 minutes 2005 Yanghee Choi 34