dhcp_response probe uses wrong MAC for DHCP requests

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Article ID: 5954

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Updated On:

Products

DX Infrastructure Management NIMSOFT PROBES

Issue/Introduction

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.

 

<Please see attached file for image>

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 

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.

Environment

UIM 8.xdhcp_response (any version)

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:

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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

 

Attachments

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