Kehribar have published his latest project – UDP bootloader for Atmega328. He used an Ethernet gateway board where Atmega328p and ENC28J60 Ethernet controller sits next to each other. UDP (User Datagram Protocol) is a transportation protocol, It doesn’t need IP settings so no need to set static (or dynamic) IP.
This is not packet based protocol, so microcontroller has to take care of error checking. Anyway this fits in to 4096 bootloadred chunk and there is a chance to make it twice smaller. Check out for latest version of bootloader in git.