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