Functions of the GIADDR field of DHCP messages on S series switches

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Functions of the GIADDR field of DHCP messages on S series switches:
he GIADDR field (gateway IP address) in DHCP messages records the IP address of the first DHCP relay agent that DHCP messages pass through. After a client sends a DHCP Request message, the first DHCP relay agent fills its own IP address in this field when forwarding this DHCP Request message to the DHCP server if the server and the client are located on different network segments. The DHCP server uses the field to determine the network segment on which a client resides so that the server can assign an IP address on this network segment to the client.

Other related questions:
Description of the GIADDR field in DHCP packets
For S series switches, the giaddr field in DHCP packets has the following function: The giaddr field (gateway IP address) indicates the IP address of the first DHCP relay agent that DHCP packets pass through. If the DHCP server and client are located on different network segments, the first DHCP relay agent fills its IP address into this field of the DHCP Request packet sent by the client and forwards the packet to the DHCP server. The DHCP server determines the network segment where the client resides based on this field, and allocates an IP address on this network segment from an address pool.

DHCP functions of S series switches
DHCP dynamically configures and uniformly manages network parameters of hosts on a TCP/IP network. DHCP provides the following functions: - Dynamic allocation: DHCP allocates an IP address with a limited validity period (called lease) to a client. This mechanism applies to hosts that temporarily connect to a network with fewer IP addresses than the total number of hosts and hosts do not need to permanently connect to the network. For example, this mechanism can be used to allocate IP addresses to laptops used by employees on business trips or mobile terminals in cafes. - Static allocation: Fixed IP addresses are assigned to specified hosts. This mechanism applies to hosts with special IP address requirements. For example, the file server of an enterprise needs to use a fixed IP address to provide services for extranet users. Compared with manual IP address configuration, DHCP static allocation prevents manual configuration errors and helps network administrators perform unified maintenance and management. DHCP can allocate other network parameters except for the IP address to hosts, including the DNS server address, routing information, and gateway address.

In which situation can an S series switch send the option field in Request messages to a client
For S series switches excluding the S1700, the DHCP server returns the corresponding option field to a client only when the corresponding option field is encapsulated in the Request message.

Meanings of the lease field in dhcp snooping command output on S series switch
For S series switches, the lease field in the outputs of DHCP snooping configuration indicates the lease of IP addresses configured on the DHCP server. The lease time varies depending on network access requirements. By default, the IP address lease is one day. - In locations where clients often move, for example, cafes, airports, and hotels, plan a short-term lease to ensure that IP addresses are released quickly after the clients go offline. - In locations where clients seldom move, for example, office areas of an enterprise, plan a long-term lease to prevent services from being affected by frequent address renewals. Different address pools on a DHCP server can be configured with different IP address leases, but the IP addresses in an address pool must be configured with the same lease. You can run the following commands to modify the lease time: - Run the dhcp server lease { day day [ hour hour [ minute minute ] ] | unlimited } command to set the lease for IP addresses in an interface address pool. For example, set the IP address lease of the address pool on VLANIF 100 to 2 days 2 hours and 30 minutes. [HUAWEI] dhcp enable [HUAWEI] interface vlanif 100 [HUAWEI-Vlanif100] ip address 10.10.10.10 24 [HUAWEI-Vlanif100] dhcp select interface [HUAWEI-Vlanif100] dhcp server lease day 2 hour 2 minute 30 - Run the lease { day day [ hour hour [ minute minute ] ] | unlimited } command to set the lease for IP addresses in a global IP address pool. For example, set the IP address lease of the global address pool global1 to 2 day 2 hours and 30 minutes. [HUAWEI] ip pool global1 [HUAWEI-ip-pool-global1] lease day 2 hour 2 minute 30

Function of DHCP Request packets on S series switch
For S series switches, DHCP Request messages are sent in the following conditions: - Respond to the DHCP Offer message sent by DHCP servers. - Notify the selected DHCP server using the server identifier option. - Check the allocated network addresses. - Apply for the valid period of addresses. - Extend the existing lease and prolong the lease period.

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