Qtech QSW-2900-24F-AC [110/209] Protocols and standards

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server picks IP addresses from the interface address pools and assigns them to the DHCP clients. If
there is no available IP address in the interface address pools, the DHCP server picks IP addresses from
its global address pool that contains the interface address pool segment and assigns them to the DHCP
clients.
· Trunk: DHCP packets received from DHCP clients are forwarded to an external DHCP server, which
assigns IP addresses to the DHCP clients.
You can specify the mode to process DHCP packets. For the configuration of the first two modes, see DHCP
Server Configuration. For the configuration of the trunk mode, see DHCP Relay Agent Configuration.
One interface only corresponds to one mode. In this case, the new configuration overwrites the previous one.
6.6 Protocols and Standards
Protocol specifications related to DHCP include:
· RFC2131: Dynamic Host Configuration Protocol
· RFC2132: DHCP Options and BOOTP Vendor Extensions
· RFC1542: Clarifications and Extensions for the Bootstrap Protocol
6.7 DHCP Relay Agent
6.7.1 Usage of DHCP Relay Agent
Since the packets are broadcasted in the process of obtaining IP addresses, DHCP is only applicable to the
situation that DHCP clients and DHCP servers are in the same network segment, that is, you need to deploy at least
one DHCP server for each network segment, which is far from economical.
The DHCP relay agent is designed to address this problem. It enables DHCP clients in a subnet to
communicate with the DHCP server in another subnet so that the DHCP clients can obtain IP addresses. In this case,
the DHCP clients in multiple networks can use the same DHCP server, which can decrease your cost and provide a
centralized administration.
6.7.2 DHCP Relay Agent Fundamentals
Figure 3-1 illustrates a typical DHCP relay agent application.

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