Announcements I HW5 online today due in 1 week HOST AUTO CONFIGURATION BOOTP DHCP Internet Protocols CSC ECE 573 Fall 2005 N C State University copyright 2005 Douglas S Reeves 2 Today s Lecture I Auto configuration II BOOTP AUTO CONFIGURATION III DHCP copyright 2005 Douglas S Reeves 3 Host Autoconfiguration Host Autoconfiguration cont d What are the networking parameters needed to configure a host Choices of configuration static in configuration file on the local disk dynamic from a server Essential Own IP address subnet mask gateway default router IP address DNS server IP address How do you ask a server to send configuration information if you don t have an IP address Many others would be useful as well copyright 2005 Douglas S Reeves 5 copyright 2005 Douglas S Reeves 6 1 Protocol Choices Minimal Reverse ARP RARP requests IP address corresponding to MAC address can only provide the client s IP address BOOTP Better BOOTP provides many other configuration parameter values Best DHCP provides limited lifetimes on configuration information copyright 2005 Douglas S Reeves 7 BOOTstraP Protocol RFCs 951 1542 BOOTP Messages Single message exchange from server to client provides many items needed at startup in addition to the IP address S2 3 Memory Image Request 4 Memory Image H1 H2 Client host uses the limited broadcast IP address 255 255 255 255 to broadcast the BOOTP Request on the local net source IP address 0 0 0 0 used only during bootstrapping S1 multi homed hosts issue one BOOTP Request for each interface 1 BOOTP Request 2 BOOTP Reply BOOTP server responds may use the limited broadcast address as destination of the BOOTP Reply BOOTP can tell clients where to get a memory image startup program copyright 2005 Douglas S Reeves copyright 2005 Douglas S Reeves 9 BOOTP Reliability BOOTP Message Format Length 236 bytes Options BOOTP runs over UDP client is responsible for ensuring reliable communication Field if no Reply after sufficient time timeout and retransmit Request wait random delay before retransmission between 0 and 4 s double timeout value each time exponential backoff 11 Bytes Interpretation Operation Type 1 Request or Reply Hardware Type 1 e g Ethernet Length of physical address 1 6 for Ethernet of Hops 1 Initialized to 0 relays increment Transaction ID 4 For matching Reply with Request Seconds since booting started 2 For prioritizing forwarding Requests 2 To indicate response should be broadcast Flags copyright 2005 Douglas S Reeves 10 copyright 2005 Douglas S Reeves 12 2 Address Fields BOOTP Message Format cont d Field Bytes Interpretation Client Request Client IP Address 4 0 if client doesn t know client fills in as many fields as known zeroes otherwise Your IP Address 4 IP address to use returned by server Server IP Address Server IP Address 4 If client wants specific server to respond Server Host Name Relay s IP Address 4 Discussed later Client Hardware Address 16 So server can unicast response to client Server Hostname 64 236 options Boot File Name If client wants specific server to respond 128 Name of file containing memory image in Request type of OS desired Options variable Client IP Address Server Reply if server specified by client only that server responds fills in whatever fields were set to zeroes by client Discussed later copyright 2005 Douglas S Reeves BOOTP Options Field 14 BOOTP Relays Encoding of each option TLV format BOOTP Relay Agents permit a machine to contact a BOOTP server on a non local network T type or tag 1 byte L length 1 byte If a server decides to relay a Request V value of option N bytes it puts its own IP interface address in the Relay IP Address field Examples of options and forwards to the BOOTP server subnet mask clients ignore the Relay IP Address field in a Reply client host name memory image size time of day gateway IP addresses DNS server IP addresses copyright 2005 Douglas S Reeves 15 copyright 2005 Douglas S Reeves 16 BOOTP Relays cont d Destination server sends Reply message to the relay agent server all Replies received by a relay agent are intended for clients on its directly connected network A Relay Agent examines the Relay IP address Your IP Address and Client Hardware Address to deliver the Reply message to the client copyright 2005 Douglas S Reeves DHCP 17 3 Dynamic Host Configuration Protocol RFCs 2131 2132 Dynamic Configuration RARP and BOOTP are designed for a relatively static environment Extends BOOTP to handle dynamic address assignment leases an address for a limited time from 1 sec to forever Problems need to assign one machine different IP addresses at different times backwards compatible with BOOTP clients message format is the same need to reuse pool of IP addresses clients only use addresses temporarily Solution dynamic address assignment mechanism copyright 2005 Douglas S Reeves copyright 2005 Douglas S Reeves 19 DHCP cont d 20 DHCP Client State Diagram DHCP server DHCPOFFER leases addresses to clients INIT REBIND REQUEST DH C pa PACK ram ete inclu d rs es DHCPACK At end of the lease period the client must either renew the lease or stop using the address SELECT select offer DHCPREQUEST informs client of lease period during which it will not lease same address to another client ER COV DIS HCP DH CP NA CK Lease reaches 87 5 of expiration time DHCPREQUEST K PAC DHC RENEW 0 s5 che time rea se ation T a e L xpir UES of e PREQ DHC BOUND copyright 2005 Douglas S Reeves 21 DHCP Client State Diagram select offer DHCPREQUEST SELECT REQUEST DH C pa PACK ram ete inclu d rs es DHCPACK REBIND BOUND DH CP NA CK Client should set Broadcast Flag to 1 if it does not have a valid IP address already DHCPOFFER message includes configuration parameters such a Your IP Address Lease reaches 87 5 of expiration time or REBIND time RENEW DHCPREQUEST K C A P DHC Same Options as BOOTP plus some additional ones 0 s5 e che rea n tim e se im tio Lea xpira AL t W T e E f o EN UES or R PREQ DHC copyright 2005 Douglas S Reeves C DH anc CP el RE le LE ase AS E D 22 Same format at BOOTP messages INIT DHCPNACK or lease expires copyright 2005 Douglas S Reeves DHCP Messages DHCPOFFER ER COV DIS HCP C DH anc CP el RE le LE ase AS E D DHCPNACK or lease expires is given a set of addresses to manage 23 copyright 2005 Douglas S Reeves 24 4 DHCPINFORM Message Some Example Options Fields If client already has IP address but requests other configuration parameters from the server Server unicasts to client a DHCPACK with parameters but Does not allocate new