DHCP service messages logged to syslog include the following:
Error messages, which notify you of conditions that prevent the DHCP service from fulfilling a request by a client or by you.
Warnings and notices, which notify you of conditions that are abnormal, but do not prevent the DHCP service from fulfilling a request.
You can increase the amount of information that is reported by using the verbose option for the DHCP daemon. Verbose message output can help you troubleshoot DHCP problems. See How to Generate Verbose DHCP Log Messages (DHCP Manager).
Another useful troubleshooting technique is transaction logging. Transactions provide information about every interchange between a DHCP server or BOOTP relay and clients. DHCP transactions include the following message types:
ASSIGN – IP address assignment
ACK – Server acknowledges that the client accepts the offered IP address, and sends configuration parameters
EXTEND – Lease extension
RELEASE – IP address release
DECLINE – Client is declining address assignment
INFORM – Client is requesting network configuration parameters but not an IP address
NAK – Server does not acknowledge a client's request to use a previously used IP address
ICMP_ECHO – Server detects potential IP address is already in use by another host
BOOTP relay transactions include the following message types:
RELAY-CLNT – Message is being relayed from the DHCP client to a DHCP server
RELAY–SRVR – Message is being relayed from the DHCP server to the DHCP client
DHCP transaction logging is disabled by default. When enabled, DHCP transaction logging uses the local0 facility in syslog by default. DHCP transaction messages are generated with a syslog severity level of notice. This security level causes DHCP transactions to be logged to the file where other system notices are logged. However, because the local facility is used, the DHCP transaction messages can be logged separately from other notices. To log the transaction messages separately, you must edit the syslog.conf file to specify a separate log file. See the syslog.conf(4) man page for more information about the syslog.conf file.
You can disable or enable transaction logging, and you can specify a different syslog facility, from local0 through local7, as explained in How to Enable and Disable DHCP Transaction Logging (DHCP Manager). In the server system's syslog.conf file, you can also instruct syslogd to store the DHCP transaction messages in a separate file. See How to Log DHCP Transactions to a Separate syslog File for more information.