DHCP address allocation in ascending order

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When functioning as a DHCP server, an S series switch allocates IP addresses to DHCP clients in descending order by default, and the order cannot be adjusted.

Other related questions:
Can the DHCP server assign IP addresses in ascending order
An S series switch used as the DHCP server assigns IP addresses to DHCP clients in descending order by default, which cannot be adjusted.

How do I check address allocation on an AR
On an AR, you can run the following commands to check address allocation: - If addresses are allocated based on the interface address pool, run the display ip pool [ interface interface-pool-name [ start-ip-address [ end-ip-address ] | all | conflict | expired | used ] ] command. - If addresses are allocated based on the interface address pool, run the display ip pool [ interface interface-pool-name [ start-ip-address [ end-ip-address ] | all | conflict | expired | used ] ] command. - If addresses are allocated based on the interface address pool, run the display ip pool [ interface interface-pool-name [ start-ip-address [ end-ip-address ] | all | conflict | expired | used ] ] command. - If addresses are allocated based on the interface address pool, run the display ip pool [ interface interface-pool-name [ start-ip-address [ end-ip-address ] | all | conflict | expired | used ] ] command. - If addresses are allocated based on the global address pool, run the display ip pool [ name ip-pool-name [ start-ip-address [ end-ip-address ] | all | conflict | expired | used ] ] command. - If all is specified, the command displays information about all IP addresses in an address pool. - If conflict is specified, the command displays information about conflicting IP addresses in an address pool. - If expired is specified, the command displays information about expired and idle IP addresses in an address pool. - If used is specified, the command displays information about used IP addresses in an address pool. - If start-ip-address [ end-ip-address ] is specified, the command displays information about a specified IP address or start and end IP addresses.

Configure active and standby DHCP servers for S series switches
The active and standby DHCP servers can be configured on S series switches (except the S1700). To improve network reliability, you can deploy two DHCP servers, one as the master server and the other as the backup server. VRRP can be configured on the two servers. When the master server is faulty, the backup server dynamically assigns IP addresses to hosts, ensuring that host services are not interrupted. In normal cases, the master device dynamically allocates IP address to clients. When the master device is faulty, VRRP triggers a master/backup switchover in which the backup device takes over the role of the master device and dynamically allocates IP addresses to clients. Real-time data backup cannot be implemented between master and backup devices in the VRRP group. To prevent IP address conflict after the master/backup switchover, the IP address ranges configured on master and backup devices must be different. In this way, after the master/backup switchover, the backup device assigns network configuration parameters such as IP addresses to newly online DHCP clients. Some clients have obtained IP addresses from the master device, and send Request messages to the DHCP server to request lease renewal. Because their IP addresses do not exist on the backup device, the backup device returns DHCP NAK messages so that these clients will apply for new IP addresses. When the original master device recovers, users can decide whether to switch service traffic back to the master device depending on the actual requirements. When configuring the DHCP server in the VRRP network, pay attention to the following items: - To implement this function, the system version is required to be upgraded to V100R006C00SPC800 or a later version. - In spite of different IP address ranges of master and backup devices in the VRRP group, both of IP address pools use the virtual IP address as the gateway. - In the two address pool views, run the exclude command to exclude real IP addresses of master and backup devices in the VRRP group to prevent address conflict. - Only a half of planned IP address segments can be used simultaneously. Therefore, the same number of extra IP addresses need to be planned, consuming large amounts of IP address resources. For configuration details about the master and backup DHCP servers, click S系列交换机:VRRP组网下同网段内配置基于全局地址池的DHCP服务器示�?.

Check address allocation on S series switch
On S series switches except S1700 switches, you can view information about IP addresses in an address pool as follows: - If an interface address pool is used, run the display ip pool [ interface interface-pool-name [ start-ip-address [ end-ip-address ] | all | conflict | expired | used ] ] command. - If a global address pool is used, run the display ip pool [ name ip-pool-name [ start-ip-address [ end-ip-address ] | all | conflict | expired | used ] ] command. You can configure fields in the command as required: - To view information about all IP addresses in an address pool, specify all. - To view information about conflicting IP addresses in an address pool, specify conflict. - To view information about expired and idle IP addresses in an address pool, specify expired. - To view information about used IP addresses in an address pool, specify used. - To view information about a specific IP address or an IP address range in an address pool, specify start-ip-address [ end-ip-address ].

DHCP overview
The Dynamic Host Configuration Protocol (DHCP) dynamically configures and uniformly manages network parameters of hosts on a TCP/IP network. DHCP supports both dynamic and static IP address allocation: - Dynamic IP address allocation: allocates an IP address with a validity period (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. 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 IP address allocation: allocates fixed IP addresses to specified clients. This mechanism applies to hosts with special IP address requirements, for example, the file server of an enterprise that 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 in unified maintenance and management. In addition to IP addresses, DHCP can also allocate other network parameters to hosts, including the DNS server address, routing information, and gateway address.

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