DHCP
Dynamic Host Configuration
Protocol
What is DHCP?
It does name resolution (one more?!)
DNS resolves IP numbers and FQDN
WINS resolves NetBIOS names and IP
numbers
ARP resolves IP numbers and MAC
addresses (outgoing packets)
DHCP resolves IP numbers and MAC
addresses dynamically
The Windows BootP
BootP is a table of IP numbers and MAC
addresses on a server
DHCP is a dynamic BootP
How does it work?
(1) DHCP discover IP scope (0)
MAC address
DHCP
CLIENT DHCP offer
IP#, lease time
DHCP DHCP
SERVER
(2) DHCP request DATABASE
IP#, MAC address
DHCP MAC address, IP#,
CLIENT DHCP ack
lease time
IP#, lease time
• Scope - a range of IP addresses
• IP lease - the IP# is assigned temporarily
• Reserved IP - servers are assigned fixed IP addresses
Pros and Cons
Pros
simplifies the task of assigning IP numbers to
each machine in the network
makes easy to add, remove or move a host
can assign defaults: default gateway, domain
name, DNS server, WINS server (if any) .
ability to have fewer IP# than hosts
Cons
if DHCP server is down, all hosts are down
hard to keep information on free and used IP #
Multi-DHCP networks
No server coordination
each subnet can only have one scope
(continuous, but you can exclude some IP
addresses), but
you can create DHCP servers with non-
overlapping scopes to the same subnet
(not MS party line)
Backup and fault tolerance
DHCP makes an hourly backup of its
database
it can recover itself, but you should do a
backup of its backup if you think
Install and setup
Install
open network in control panel, select
services
add MS DHCP Server, press OK and close
system will need to reboot, do it
when re-starts DHCP is installed and
started as a service
Setup
open DHCP Manager and select create
scope
enter the range of IP# and exclusions as
shown
DHCP and IPCONFIG
IPCONFIG/ALL
FQDN, servers (DNS, WINS), node type, etc
NIC description, MAC address, IP address,
gateway, subnet mask
To handle leases
IP CONFIG/RENEW [adapter]
IP CONFIG/RELEASE [adapter]
if no adapter name is specified, then the IP
leases for all adapters bound to TCP/IP will
be released or renewed.