АМАТЕК AN-SGM28P24-400 [207/322] Dhcp snooping specifies the physical port of

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type is REQ, the IP address, the MAC address, the interface information, and the 10 second delay

timer are set up。

When the DHCPrequest message is received, the REQ type binding table entries already exist,

the entries are updated, and the delay timers are restarted。

When the DHCPrequest message is received, the ACK type binding table entry already exists,

then the interface information is recorded。

When receiving the DHCPack message, if there is a REQ type binding table entry, the IP

address allocated by the server in the DHCPack message is recorded, the delay timer is closed, and

the lease timer is started。

When receiving the DHCPack message, there is no REQ type binding table entry, and then

the message is dropped。

When DHCPack packets are received, ACK type binding table entries already exist. If the

interface has changed, the binding table entries of the original interface are deleted, and the entries

are updated。

If the interface does not change, the IP address assigned by the server changes, deleting the

binding table entries of the original interface and updating the entries。

If the interface does not change, the IP address has not changed, indicating that the renewal

process, restart the lease timer can be。

When the timeout timer expires, the REQ type binding table entries are deleted。

When the lease timer timeout, the ACK type binding table entries are deleted。

15.1.3 DHCP SNOOPING specifies the physical port of

the linked server

DHCP SNOOPING specifies the physical port of the linked server, and only the DHCP

message can be received on the specified port. If there are multiple DHCP servers in the network,

the OFFER provided by the server from the non specified port will be filtered, and the IP address

can not be assigned to the client. Designated ports are conducive to the unified allocation of IP

addresses in the network, to avoid the unknown server address pool is not in the IP planning, some

clients can not normally connect to the network. To some extent, it reduces the probability of

network communication anomalies caused by unauthorized access to the server。