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DHCP status shows poisened entries

Issue:  The "dhcp x status" command shows some entries with a "poisened" status.  For example:

dhcp 0 status 
Entry: IP [], hostname [hostexample1], MAC [11:11:11:11:11:11], expiry 4318 (mins)
Entry: IP [], hostname [hostexample2], MAC [22:22:22:22:22:22], expiry 14 (mins), poisened
Entry: IP [], hostname [hostexample2], MAC [22:22:22:22:22:22], expiry 4319 (mins)

Cause:  The TransPort should perform an ARP request on an IP address before it assigns that IP address to a DHCP Client.  If an unexpected ARP response is received, the address is "poisened" for 15 minutes, meaning that the TransPort's DHCP Server will not issue an IP address to that Client for that period of time.

An unexpected ARP response may be due to the TransPort's DHCP Server not necessarily knowing if devices on the network already own an address that is within the DHCP pool.  Examples of this are the TransPort's DHCP Server losing memory of addresses it has handed out, some other DHCP Server handing out the same address, or some device having a statically configured, conflicting IP address

Resolution:  Enable the DHCP Server's "ipdd" feature, which checks if IP addresses are in use before they are issued:

dhcp 0 ipdd ON
config 0 save

NOTE: The default value of "ipdd" is OFF.

A related command that may require adjustment:

dhcp 0 ipddretx x
config 0 save

NOTE:  'x' is the number of attempts the check will perform.  The default value of "ipddretx" is 0.

Last updated: Jan 04, 2024

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