%Error opening tftp://255.255.255.255/network-confg (Timed out)

Are you getting the error messages:

• %SYS-4-CONFIG_RESOLVE_FAILURE: System config parse from (tftp://255.255.255.255/network-confg) failed
• %Error opening tftp://255.255.255.255/network-confg (Timed out)

These messages threw me for a loop the first time.

This “feature” happens because your router senses carrier detect on a serial interface and uses the Cisco proprietary protocol called SLARP (serial link ARP). Once it find the remote end IP, the interface on your router assigns itself the next IP address in the range, and enables itself.

Now remember, the router thinks it is doing you a favor here….but wait, it’s not done trying to help you out.

After it finds the neighbors IP address and assigns your interface an IP address and enables it, the router then tried to do a reverse DNS lookup using that IP Address, that is the 255.255.255.255 you see over and over again. If by chance that it finds a DNS server and resolved the IP address to a name, it assigns that name as the hostname of your router. At this point the router will then broadcast looking for a DNS server looking for a configuration with the hostname that it found with an extension of hostname-confg. If it find this on the tftp server, if downloads it and puts it in running-config. Your router is supposedly up and running.

This “feature” was helpful about 15-19 years ago (early 1990’s), but has outlived its usefulness since more than one person in the world can now configure a Cisco router. At the time, there was maybe 100-150 Cisco techs in the world, so this could be useful if setup correctly.

To disable this use these two commands from global config:

• no service config
• no boot network