Network Protocols Dynamic Host Configuration Protocol DHCP TDC

Network Protocols Dynamic Host Configuration Protocol (DHCP) TDC 375 Autumn 03/04 John Kristoff - De. Paul University 1

Bootstrapping and auto-config • Host loads boot image and/or config from network • Station needs to know its own IP address • Station only knows its hardware address • Station minimally needs: • Its IP address • The default gateway/router • Its subnet mask • . . . and a DNS server (or more) would be nice TDC 375 Autumn 03/04 John Kristoff - De. Paul University 1

Older, less popular methods • Reverse ARP (RARP) • • ICMP info/mask/router queries • • What is the IP address for MAC xxxx. yyyy. zzzz What is my IP, mask and router? BOOTP • What is my config (and maybe boot loader file)? TDC 375 Autumn 03/04 John Kristoff - De. Paul University 1

To get configuration remotely • • Broadcast request • no source IP yet, use 0. 0 (this net, this host) • destination? use 255 (limited bcast) Receive response • From a configuration server • Sends to our MAC, since we don't have a IP yet • Routers can intercept/forward to remote servers TDC 375 Autumn 03/04 John Kristoff - De. Paul University 1

Typical DHCP startup behavior Client Server DHCP-DISCOVER-> <-DHCP-OFFER DHCP-REQUEST-> <-DHCP-ACK DHCP-RELEASE-> TDC 375 Autumn 03/04 John Kristoff - De. Paul University 1

DHCP packet format TDC 375 Autumn 03/04 John Kristoff - De. Paul University 1