3Com 10014299 manual Dhcp Server Configuration, Fault Ping Two PCs, but fails to ping them through

DHCP Server Configuration 333

connected with PC must be set as “untagged” for the reason that PC cannot identify data packet marked with VLAN tag.

Fault: Ping Two PCs, but fails to ping them through.

Troubleshooting: The steps below can be taken.

■First, ping the IP address of Ethernet subinterface in the same VLAN from a PC. If the ping fails, solve the problem according to the method described in fault one.

■If one PC can ping through the IP address of Ethernet subinterface in the same VLAN, but fails to ping through another PC, please use the command route print in MS-DOS of the two PCs to see if the route to peer PC is available. If not, please add the relevant route.

DHCP Server Configuration

Background of the DHCP development

As the scale of networks grows and their complexities increase, network configurations become more and more complex. The original BOOTP protocol for static host configuration cannot satisfy the demands of users, especially on the occasions when computers are always on the move (e.g., using laptops or wireless network) and the number of actual computers exceeds that of the available IP addresses. To facilitate users to improve utilization ratio of resources and to support diskless networking mechanisms, the DHCP (Dynamic Host Configuration Protocol) based on BOOTP was developed. Similar to the BOOTP protocol, DHCP works in client-server mode. With this protocol, a DHCP client can dynamically request configuration information from a DHCP server, including important parameters such as assigned IP addresses, subnet masks and default gateways, etc. DHCP server can also conveniently configure this information dynamically for DHCP clients.

DHCP vs BOOTP

■Both BOOTP and DHCP adopt the client/server communication mode. A client applies to the server for configurations (including the configurations of important parameters such as allocated IP address, subnetmask, and the default gateway). Then, the server will return the corresponding configuration information according to the policies. Both types of packets are encapsulated with the UDP packets. Furthermore, their structures are almost the same.

■BOOTP is running in a relatively static (every host is connected by a permanent network) environment. Hence, administrators should configure special BOOTP parameter files for each host and then, these files will stay the same for a relatively long time.

■DHCP extends the BOOTP from two aspects: DHCP enables computers to obtain all the needed configuration information by using one message and it allows computers to rapidly and dynamically obtain IP addresses so to avoid statically specifying addresses for each host by BOOTP.

IP address allocation policy provided by DHCP

Different hosts have different application requirements. For example, some servers perhaps need to use the fixed IP addresses for a long time, some hosts need to use certain IP addresses dynamically allocated for a long period of time and some individuals can arbitrarily use the allocated temporary IP addresses. A