|
DHCP
1. DHCP protocol defined in RFC2131 species, use the udp protocol for data transmission is reported, the use of the port is 67 and 68.
2. DHCP most common application is automatically allocated to the terminal equipment ip address, mask, default gateway, DHCP but also to the terminal equipment can automatically configure other options, such as DNS server, domain name (such as net130.com), time zones, NTP servers, as well as other configuration of the content, but also some manufacturers use their own 3rd release software, some of their configuration information, using dhcp to achieve agreement on terminal equipment automatic configuration.
3. DHCP service system is the most basic framework for client / server model, and if the client and the server is no longer with a 2-layer network (ie, radio can reach the network), you must be able to broadcast the message in Following the equipment, or can broadcast message text into a single broadcast equipment.
There are three distinct element types in a DHCP network. There must be a client and a server. If these two elements are not on the same Layer 2 network, there also must be a proxy, which usually runs on the router. The proxy is needed because the client device initially doesn't know its own IP address, so it must send out a Layer 2 broadcast to find a server that has this information. The router must relay these broadcasts to the DHCP server, then forward the responses back to the correct Layer 2 address so that the right end device gets the right configuration information.
4. CISCO router (IOS12.0 T1 later), can be configured to dhcp relay equipment, DHCP client devices can also be configured as DHCP servers.
5. same network segment can have more than one DHCP server, this will not affect the terminal equipment from the server to obtain configuration information, terminal equipment to receive the first group of configuration information shall prevail. Paragraph after the return of the DHCP server configuration information is discarded.
Most DHCP networks of any size include two or more DHCP servers for redundancy. The end devices typically just need to talk to a DHCP server at startup time, but they will not work at all without it. So redundancy is important. This also means that it is not unusual for an end device to see several responses to a DHCP request. It will generally just use the first response. However, this also underscores the importance of ensuring that all of the DHCP servers distribute the same information. Their databases of end device configuration parameters must be synchronized.
6. DHCP server is often first-come, first serve to comply with the rules (first-come, first-served), or that he was able to build a terminal device IP address and MAC address mapping between the table (or called the database), which can guarantee a specific terminal (that is, a specific MAC) after each boot will be able to obtain this same ip address.
The server can allocate IP addresses from a pool on a first-come, first-served basis, or it can associate IP addresses with end device MAC addresses to ensure that a particular client always receives the same address.
|