convert .bin download to .trx - instructions at https://forum.openwrt.org/viewtopic.php?id=12248
dd bs=32 skip=1 if=linksys.bin of=linksys.trx
confirm file now begins at byte 0 with HDR0::
$ hexdump -C openwrt-wrt54g-squashfs.bin | grep HDR0
then uploaded bin using scp
then installed using mtd:
mtd -r write firmware.trx linux
by default it's configured to bridge lan and wireless.
i just disabled DHCP, gave it a static IP, DNS and default gw.
configured wireless SSID + auth same as the other router in the house.