dhcp_response probe uses wrong MAC for DHCP requests

Document ID : KB000005954
Last Modified Date : 14/02/2018
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Issue:

After installing the dhcp_response probe, you might notice that the probe GUI does not show a list of DHCP servers even though the robot where the probe is deployed to received an IP address from the DHCP server.

 gui_dhcp_response_probe.JPG

 If you then  enable the level 5 logs for the probe, you will see the actual broadcast from the probe, and it will contain a MAC address that is not paired with the IP address that is being used by the robot.

 

Example:

dhcp_response: DHCP - DHCPDISCOVER broadcast sent  

dhcp_response: ------------------------------------------------------------------ 

dhcp_response: Message type...........: DHCPDISCOVER  (BOOTREQUEST) 

dhcp_response: Harware type...........: ETHER 

dhcp_response: Hardware address lenght: 6 

dhcp_response: Hops............: 0 

dhcp_response: Transaction ID..: 2220887955l 

dhcp_response: Seconds elapsed.: 0 

dhcp_response: Flags...........: 8000 

dhcp_response: Client IP.......: 0.0.0.0 

dhcp_response: Your IP.........: 0.0.0.0 

dhcp_response: Server IP.......: 0.0.0.0 

dhcp_response: Relay Agent IP..: 0.0.0.0 

dhcp_response: Hardware address: D8-8B-5C-09-D1-DF

dhcp_response: Server host.....:  

dhcp_response: Boot file.......:  

dhcp_response: Option 53: DHCP Message Type = DHCPDISCOVER 

dhcp_response: Option 61: Client ID = 01 d8 8b 5c 09 d1 df 

dhcp_response: Option 55: Parameter Request List = 1 15 3 6 44 46 47 51  

 dhcp_response: dhcp_sendto: 548 bytes sent to 255.255.255.255 

Environment:
UIM 8.xdhcp_response (any version)
Cause:

On a cluster machine the dhcp_response probe is not able to determine which interface it should be using to run the DHCPDISCOVER broadcast and might use an incorrect MAC address. If that MAC address is not paired with an IP that was provided by a DHCP server, it will not respond to the broadcast and no data is being returned.

Resolution:

As a workaround, you would need to force the dhcp_response probe to use a specific MAC address.  In IM or admin console, please open the probe in "raw configure" mode, and add a new key / value pair in the "setup" section. 

Key:  MAC

Value: your desired MAC address

 

Example:

dhcp_response_raw_configure.PNG 

Once you have added this entry, you would need to apply the changes and restart the probe. The probe should now use the desired MAC address and receive a valid response to the DHCPDISCOVER  broadcast, allowing the probe to populate the list of available DHCP servers.

Additional Information:

The dhcp_response probe documentation is available here:

https://docops.ca.com/ca-unified-infrastructure-management-probes/ga/en/alphabetical-probe-articles/dhcp_response-dhcp-server-response