What is the relationship between BOOTP and DHCP server?

In our previous studies on network protocols, we found that some references are explained by combining the BOOTP protocol, DHCP protocol, and DHCP server. So what is the relationship between DHCP and BOOTP? BOOTP relay proxy BOOTP (Bootstrap Protocol) relay proxy is an Internet host or router that transmits DHCP messages between the DHCP server and the DHCP client. The BOOTP protocol is designed for remote guidance, mainly to notify the location of the client boot file to be connected.

DHCP is an extension of the BOOTP mechanism. This feature means that the existing BOOTP client can interact with the DHCP server without changing the installed software. RFC 1542 details the interaction between the BOOTP, DHCP client, and DHCP server. DHCP works in client/server mode like BOOTP. With this protocol, the DHCP client can dynamically request configuration information from the DHCP server, including the assigned IP address, subnet mask, default gateway, and other important parameters, the DHCP server can also configure the information dynamically. DHCP provides a solution framework for setting hosts on TCP/IP networks. DHCP inherits from BOOTP and adds the function of automatically allocating reusable network addresses and adding configuration options. DHCP has a BOOTP relay proxy. DHCP users and BOOTP users can perform interactive operations.

The DHCP Message format is based on the BOOTP message format, so as to have the behavior of the relay proxy and allow the existing BOOTP client and DHCP server to have the ability to collaborate (interuse ), using the BOOTP relay proxy avoids the need for a DHCP server in each physical network segment .. DHCP defines a mechanism through which the client can assign a network parameter with a certain lease period. In addition, we consider the continuous redistribution of network addresses for different clients.

DHCP provides a mechanism to allow the client to obtain parameters configured for all IP addresses for operation. Introduction to the DHCP principle as the network scale expands and the complexity of the network increases, the network configuration becomes more and more complex, and computer locations (such as hosts or wireless networks) change frequently) and the number of computers exceeds the allocated IP address. Dynamic Host Configuration Protocol (DHCP) is developed to meet these needs. The DHCP protocol works in client/server mode. The DHCP client dynamically requests configuration information from the DHCP server. The DHCP Server returns the corresponding configuration information (such as IP addresses) according to the policy) A typical DHCP Application generally contains one DHCP server and multiple clients (such as PCs and laptops ).

Dhcp ip Address Allocation

1. IP Address Allocation Policy

Different clients have different requirements for the time occupied by IP addresses: for servers, you may need to use a fixed IP address for a long time; for some hosts, you may need to use a dynamically assigned IP address for a long time; some individuals may only assign a temporary IP address as needed.

Manual Address Allocation: The administrator configures a fixed IP address for a few specific clients (such as WWW servers.

Automatic Address Allocation: assign a fixed IP address to some clients that connect to the network for the first time. This address will be used by the client for a long time.

Dynamic Address Allocation: assign an address to the client by leasing. After the expiration time, the client needs to apply for a new address. Most clients obtain such dynamically allocated addresses.

2. IP Address Allocation priority

In the following order, the DHCP server selects an address other than the forbidden-IP address for the client:

Static IP address bound to the client MAC address in the address pool of the DHCP server;

The IP address used by the client before, that is, the address of the Request IP address Option (Requested IP Addr Option) in the DHCP_Discover packet sent by the client;

In the DHCP address pool, find the IP addresses available for allocation in sequence, and find the IP addresses first;

If no available IP addresses are found, the IP addresses that have exceeded the lease term and conflict are queried in sequence. If yes, the IP addresses are allocated. Otherwise, an error is reported.

3. DHCP server address pool type

Global address pool: valid in this switch. It is created using the dhcp server ip-pool command in the System View.

VLAN interface address pool: valid in this VLAN interface. A valid unicast IP address is configured for the vlan interface, in addition, in the VLAN interface view, use the dhcp select interface command to set the IP address allocated from the vlan interface address pool, and then the system creates the IP address range, which is the network segment of the vlan interface.

Interaction between the DHCP client and the server

To obtain valid Dynamic IP addresses, the DHCP Client interacts with the server in different stages. There are usually three modes:

1. The DHCP client logs on to the network for the first time.

When a DHCP client logs on to the network for the first time, it establishes contact with the DHCP server through four phases.

Discovery stage: the stage in which the DHCP client looks for a DHCP server. The client sends the DHCP_Discover packet in broadcast mode, and only the DHCP server responds.

The provision phase, that is, the IP address provided by the DHCP server. After the DHCP server receives the DHCP_Discover packet from the client, it selects an unallocated IP address from the IP address pool and assigns it to the client, and sends the DHCP_Offer packet containing the rental IP address and other settings to the client.

Select a phase, that is, the phase in which the DHCP Client selects an IP address. If Multiple DHCP servers send DHCP_Offer packets to the client, the client only accepts the first DHCP_Offer packet received, and then broadcasts the DHCP_Request packet to the DHCP servers, this information contains the IP Address requested from the selected DHCP server.

The validation phase, that is, the phase in which the DHCP server confirms the IP addresses provided. When the DHCP server receives the DHCP_Request packet from the DHCP client, it sends the DHCP_ACK validation packet containing the IP address provided by the DHCP Client and other settings to the client. Then, the DHCP client binds its TCP/IP protocol component to the NIC.