What are address allocation rules for S series switches

When functioning as a DHCP server, an S series switch (excluding the S1700) adds IP addresses in an address pool to different IP address lists based on the IP address status. Unallocated IP addresses belong to the allocatable IP address list. Allocated IP addresses belong to the in-use IP address list. Conflicting IP addresses belong to the conflicting IP address list. IP addresses that cannot be allocated belong to the unallocatable IP address list. The DHCP server selects an IP address for a client from the address pool in the following sequence:
1. IP address statically bound to the MAC address of the client on the DHCP server
2. IP address that has been allocated to the client
3. IP address specified in the Option50 field (requested IP address) in the DHCP Discover message from the client
4. Largest allocatable IP address
5. If the DHCP server does not find any allocatable IP address, it searches for the expired IP addresses and conflicting IP addresses in turn, and then allocates a valid IP address to the client. If all the IP addresses are in use, the DHCP server replies with a DHCP NAK message to notify the client that no IP address is available. After receiving the DHCP NAK message, the DHCP client sends a DHCP Discover message to apply for a new IP address.

The device can exclude some IP addresses that cannot be allocated through DHCP from address pools. For example, if IP segment has been manually configured for the DNS server, the DHCP server needs to exclude this IP address from the address pool on network segment In this way, IP address will be not allocated through DHCP, preventing IP address conflicts.

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