100GBase-KR4 is a 100GbE interface for backplane Ethernet for bandwidth requirements in blade servers. It is an interface for 100 Gigabit Ethernet for a point-to-point connection via the traces of the backplane PCB.
The 100GBase-KR4 interface operates at 4 x 25 Gbps over backplanes and is said to be capable of bridging distances of 1 meter. It was specified by the 802.3baworking group.
Since there are no specifications for 100 Gigabit Ethernet over backplanes, the IEEE 802.3bj working group is concerned with backplane Ethernet over four lanes via four differential copper lines with 25 Gbit/s each.