2. DHCP
A host need an IP Address and some other piece of information (subnet mask,
gateway address, etc…) to send the packets.
Normally this information’s are provided by the system administrator and
configure in manually.
But for a large network it is complex and error prone. So automatic
configuration method is used.
Automatic configuration is provided by DHCP.
It needs a DHCP server to provide the information dynamically.
DHCP Server – It is a central repository for host configuration details.
3. DHCP
Steps,
A newly booted or attached host sends a “DHCP DISCOVER”
message to special IP Address 255.255.255.255 (Broadcast Address).
DHCP relay receives this request and unicast that request to the
DHCP server.
DHCP relay – It contains the IP address of DHCP Server.
DHCP server sends back the response to the requesting client.
4. DHCP
DHCP dynamically assigns IP address to hosts. But host cannot keep
addresses indefinitely.
Thus DHCP allows addresses to be “leased” for some period of time.
Once the lease expires, client needs to renew the IP Address.
Advantages,
Scaling of network management
Improves manageability of a network.
7. DHCP
Operation Code (8 bit) – specifies whether the message is request
(1) / response (2).
Hardware Type (8 bit)–Specifies the type of hardware used for local
network (value 1 – Ethernet).
Hardware Address Length (8 bit)–Specifies the length of the
hardware address.
8. DHCP
Hops (8 bit) – Used to control the DHCP request message by DHCP
relay.
Transaction Identifier (32 bit) – XID - A 32-bit identification field
generated by the client, to allow it to match up the request with
replies received from DHCP servers.
9. DHCP
Seconds (16 bit) -number of seconds elapsed since a client began an
attempt to acquire or renew a lease.
Flag (16 bit) –B bit is set to 1 to represent the broadcast message.
Other bits are set to Zero.
Client IP Address - The client puts its own current IP address in this
field if and only if it has a valid IP address while in the renewing state.
10. DHCP
Your IP Address - The IP address that the server is assigning to the
client.
Server IP Address –Address of the DHCP server.
CHAddr –Client Hardware Address - The hardware address of the
client, which is used for identification and communication.
SName –Server Name – Name of the DHCP server, provided by the
server during the response.