1. Unit 2 dhcp, apipa and ntp

2. Static vs dynamic ip addressing
Static IP address
IP has been manually entered into the computer
If two computers are assigned the same IP, this can cause a problem
You can use a static IP for the following:
Voice Over Internet Protocol (VOIP)
Virtual Private Network
Servers printers

3. Static vs dynamic ip addressing cont’d…
Dynamic IPs are usually given out by your ISPs, the DHCP servers can assign IPs to people on the network.
You should never use a dynamic IP on your VOIP, VPN, Servers, Printers as the IP changes often and this would make them less reliable than static IP address.
You could get disconnected when using the service

4. Bootstrap protocol(BOOTP)
IP address used to be manual
IP address, subnet mask, gateway, DNS servers, NTP servers, etc.
October 1993 – The bootstrap protocol
BOOTP – when computers start by its bootstrap running the protocol automatically to get some address
BOOTP didn’t automatically define everything
Some manual configurations were still required

5. Bootstrap protocol(BOOTP) cont’d…
BOOTP also didn’t know when an IP address might be available again
Dynamic Host Configuration Protocol (BOOTP successor)
Initially released in 1997
Updated through the years

6. Dynamic host configuration protocol
DHCP provides an automated way to distribute and update IP addresses and other configuration information on a network.
A DHCP server provides this information to a DHCP client through the exchange of a series of messages, known as the DHCP conversation or the DHCP transaction.
If the DHCP server and DHCP clients are located on different subnets, a DHCP relay agent is used to facilitate the conversation.

7. Configuring DHCP
The Dynamic Host Configuration Protocol (DHCP) provides an automatic address configuration for clients.
It can supply each client with an IP address and subnet mask, plus additional parameters such as default gateway, DNS servers, and so on.
DHCP is normally provided as part of the network operating system or through an appliance such as a layer 3 switch or router.

8. Configuring DHCP cont’d…
A DHCP server must be allocated a static IP address and configured with the following information: - A range of IP addresses to allocate (its scope)
- A lease period plus renewal (T1) and rebinding (T2) timers. - A subnet to allocate. - Other optional information to allocate, such as default gateway and DNS address(es).

9. DHCP Scopes and Leases Leasing your address Allocation Reallocation
Its only temporary
But it can seem permanent
Allocation
Assigned a lease time by the DHCP server
Administratively configured
Reallocation
Reboot your computer
Confirms the lease

10. DHCP Scopes and Leases cont’d…
Workstation can also manually release IP address
Moving to another subnet (wire/wireless)
T1 Timer
Check in with the lending DHCP server to renew the IP address
50% of the lease time (by default)
T2 Timer
If the original DHCP server is down, try rebinding with DHCP server
87.5% of the lease time

11. DHCP Options A special field in the DHCP message
Many, many, options
Options are part of the DHCPRFC
BOOTP called them “vendor extensions”
256 (254 usable) options
0 through 255
0 is reserved pad, 255 is reserved end

12. DHCP Options cont’d… Many common options
Subnet mask, domain name server, domain name
Options are configured on the DHCP server
Not all DHCP servers support option configuration

13. DHCP Reservations Dynamic allocation Automatic allocation
DHCP server has a pool of addresses to give out
Addresses are reclaimed after a lease period
Automatic allocation
Similar to dynamic allocation
DHCP server keeps a list of past assignments
You will always get the same IP address

14. DHCP Reservations cont’d…
Static allocation
Administratively configured
Table of MAC addresses
Each MAC address has a matching IP address
Other names
Static DHCP Assignments
Static DHCP
Address Reservation
IP reservation

15. This is a mapping of a MAC address to a specific IP address.
When the DHCP server receives a request from the given MAC address, it always provides the same IP address.

16. Network Time Protocol (NTP)
NTP is a protocol that is used to synchronize computer clock times in a network of computers
Assigns time to devices such as router
Uses UCT as reference time
NTP applies to both the protocol and the client/server programs that run on computers