Why does dhcp use udp

The first thing you should do, as mentioned, is to make sure that DHCP has been enabled on your server. Make sure to check both IPv4 and IPv6 when doing this.

Since the default DHCP address range is between and , you'll want to avoid all of the addresses between That leaves the ranges from and from wide open, which is usually plenty for most home networks.

What are the 4 steps of DHCP? These stages are often abbreviated as DORA for discovery, offer, request, and acknowledgement. UDP port number 67 is the destination port of a server, and UDP port number 68 is used by the client. Relay agents are used to forward requests and replies between clients and servers when they are not on the same physical subnet.

A DHCP server dynamically assigns an IP address and other network configuration parameters to each device on a network so they can communicate with other IP networks.

As the requesting client has no IP address when joining the network, it broadcasts the request. The protocol is thus used in a very early stage of IP communication. The period of validity is called the DHCP lease time. To avoid impacts of the DHCP server not being available at the end of the lease time, clients generally start renewing their lease halfway through the lease period. When a server replies to a client message it does not generate the reply as a completely new message, but rather copies the client request, changes fields as appropriate, and sends the reply back to the client.

A special transaction identifier XID is placed in the request and maintained in the reply, which allows a client know which reply goes with a particular request. It also has many of the same addressing concerns that we discussed in the topic on BOOTP messaging and addressing. Clients usually will send requests by broadcast on the local network, to allow them to contact any available DHCP server. The exception to this is when a client is trying to renew a lease with a server that it already knows.

Please Whitelist This Site? This field is a maximum of bytes in length and contains the DHCP message type and configuration parameters allocated by a DHCP server to a client. The options are sent in a variable-length field at the end of a DHCP message. This field consists of Type, Length, and Value, which are shown in Figure and described in Table The values of the Options field range from 1 to Some DHCP options are predefined and others can be user defined.

Table lists some of the common predefined DHCP options. Specifies a group of classful static routes that the DHCP client must add to its routing table. In classful static routes, destination address masks are natural masks and cannot be used for subnetting.

If Option is configured, Option 33 is ignored. Specifies a parameter request list. A DHCP client uses this option to request specified configuration parameters. Specifies a group of classless static routes that the DHCP client must add to its routing table. In classless static routes, destination address masks can be any value and can be used for subnetting. In addition to the predefined options, you can configure user-defined options to support a wide variety of devices, such as IP phones.

Option 43 is called the vendor-specific information option. Figure shows the format of Option Sub-option type: type of the sub-option. The DHCP server that supports the Option 82 field can determine policies to allocate IP addresses and other parameters according to information in the Option 82 field. IP addresses can be allocated flexibly.