Unit 2 dhcp, apipa and ntp

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

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

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

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

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.

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.

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).

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

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

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

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

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

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

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.

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