Bootstrap And Autoconfiguration (BOOTP, DHCP)

System Startup IP stack designed with many parameters IPv4 or IPv6 address an address mask, network prefix, addresses of a default router addresses of a name server. Values filled in when system starts

Two possible sources of information System Startup Two possible sources of information Local storage device (e.g., disk) Server on the network

RARP ???

RARP - Disadvantage direct access to the network hardware reply contains only one small piece of information, client's 4- octet IP address it cannot be used on networks that dynamically assign hardware addresses.

BOOTstrap Protocol (BOOTP) Dynamic Host Configuration Protocol (DHCP) Neighbor Discovery Protocol (NDP, IPv6 – ND)

BOOTstrap Protocol (BOOTP) Early alternative to RARP BOOTP operates in the client-server paradigm and requires only a single packet exchange. Obtained configuration parameters from a server - IP address, the address of a router, and the address of a server. Used UDP

Using IP To Determine An IP Address BOOTP uses UDP to carry messages and that UDP messages are encapsulated in IP datagrams for delivery. Destination ?? 255.255.255.255 Reply??

The BOOTP Retransmission Policy UDP uses IP for delivery messages can be delayed, lost, delivered out of order, or duplicated To guard against corruption, BOOTP requires that UDP use checksums. To handle datagram loss, BOOTP uses the conventional technique of timeout and retransmission

BOOTP Message Format

Dynamic Host Configuration Protocol (DHCP)

Replaces and extends BOOTP DHCP Replaces and extends BOOTP

DHCP DHCP allows a computer to acquire all the configuration information it needs in a single message IP with Subnet Mask

DHCP allows a computer to obtain an IP address quickly and dynamically manager must configure a DHCP server by supplying a set of IP addresses.

DHCP DHCP used to obtain parameters for an IP stack DHCP uses IP and UDP to obtain the parameters Stack must be initialized before being initialized

DHCP runs as application Using IP To Determine An IP Address Limited Broadcast Using IP To Determine An IP Address Uses UDP to carry messages

Retransmission Policy Client handles retransmission Initial timeout selected at random Timeout for successive retransmissions doubled

DHCP Server not in Local Network?? Relay Agent

DHCP address assignment manual configuration manager can configure specific address for a specific computer automatic configuration DHCP server assign a permanent address when a computer first attaches to the network dynamic configuration server "loans" an address to a computer for a limited time

Dynamic Address Assignment Client is granted a lease on an address Server specifies length of lease At end of lease, client must renew lease or stop using address Actions controlled by finite state machine

DHCP Address Acquisition States

DHCP Message Format

DHCP Options And Message Type