If you use UDP-based syslog servers, you might have noticed that they miss a message or two generated during a router reload (particularly when the syslog server is on a directly connected LAN). The reason is simple - when the first message is sent to the syslog server, its MAC address is not yet in the router's ARP cache and the message is dropped. To prevent the message loss, you can use the logging server-arp configuration command (introduced in IOS release 12.3T), making sure that the router sends ARP request to the configured syslog server(s) before generating the first syslog messages.

Note: this issue does not occur when using TCP as the syslog transport mechanism.