Some targets allow GDB to connect via Ethernet - if so, it will be mentioned in the document describing the target. Substitute the target's assigned IP address or hostname for <hostname> in the following. Depending on how RedBoot has been configured, it will either have this address allocated statically, or will acquire it via BOOTP. In both cases RedBoot will report the IP address it is listening on in its startup message printed on the serial port. The <port> is the TCP port which RedBoot is listening on, usually 9000. It is also listed in the target document.
Connect to the target by issuing the following command in GDB console mode:
(gdb) target remote <hostname>:<port>
In Insight, connect by opening the File->Target Settings window and enter:
Target: Remote/TCP Hostname: <hostname> Port: <port>
Set other options according to preference, close the window and select Run->Connect to target.