The DHCP service can log DHCP service messages and DHCP transactions to syslog. See thesyslogd(1M) andsyslog.conf(4) man pages for more information about syslog.
DHCP service messages logged to syslog include:
Error messages, which notify the administrator of conditions that prevent the DHCP service from fulfilling a request by a client or by the administrator.
Warnings and notices, which notify the administrator of conditions that are abnormal, but do not prevent the DHCP service from fulfilling a request.
You can increase the amount of information reported by using the verbose option for the DHCP daemon. Verbose message output can be useful in troubleshooting 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:
ASSIGN – IP address assignment
ACK – Server acknowledges that 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:
RELAY-CLNT – Message being relayed from the DHCP client to a DHCP server
RELAY–SRVR – Message being relayed from the DHCP server to the DHCP client
Transaction logging is disabled by default. When enabled, transaction logging uses the local0 syslog facility by default. DHCP transaction messages are generated with a syslog severity level of notice, so by default, transactions are logged to the file where other notices are logged. However, because they use a local facility, the transaction messages can be logged separately from other notices if you edit the syslog.conf file to specify a separate log file.
You can disable or enable transaction logging, and specify a different syslog facility, from 0 through 7, as explained in How to Enable and Disable DHCP Transaction Logging (DHCP Manager). If you edit the server system's syslog.conf file, you can also instruct syslogd to store the DHCP transaction messages in a separate file, as explained in How to Log DHCP Transactions to a Separate syslog File.