I’m trying to install OpenWRT on a RB750UPr2. Sorry if that makes me a little unpopular around here 
Installation is failing at the initramfs state. I set up my host machine with a DHCP and TFTP server, then go into the router’s RouterOS and set try-ethernet-then-nand, set boot protocol to dhcp, and check Force Backup Booter. Then reboot with a cable between my host machine and the router’s port one, and see this output from dnsmasq:
1244678098 available DHCP range: 192.168.1.50 -- 192.168.1.150
1244678098 vendor class: Mips_boot
1244678098 DHCPDISCOVER(enp3s0) e4:8d:8c:dd:27:83
1244678098 tags: known, enp3s0
1244678098 DHCPOFFER(enp3s0) 192.168.1.60 e4:8d:8c:dd:27:83
1244678098 requested options: 1:netmask, 3:router
1244678098 bootfile name: /srv/tftp/openwrt-ar71xx-mikrotik-vmlinux-initramfs.elf
1244678098 server name: boothost
1244678098 next server: 192.168.1.5
1244678098 sent size: 1 option: 53 message-type 2
1244678098 sent size: 4 option: 54 server-identifier 192.168.1.5
1244678098 sent size: 4 option: 51 lease-time 12h
1244678098 sent size: 4 option: 58 T1 6h
1244678098 sent size: 4 option: 59 T2 10h30m
1244678098 sent size: 4 option: 1 netmask 255.255.255.0
1244678098 sent size: 4 option: 28 broadcast 192.168.1.255
1244678098 sent size: 4 option: 3 router 192.168.1.5
1231716188 available DHCP range: 192.168.1.50 -- 192.168.1.150
1231716188 vendor class: Mips_boot
1231716188 DHCPREQUEST(enp3s0) 192.168.1.60 e4:8d:8c:dd:27:83
1231716188 tags: known, enp3s0
1231716188 DHCPACK(enp3s0) 192.168.1.60 e4:8d:8c:dd:27:83
1231716188 requested options: 1:netmask, 3:router
1231716188 bootfile name: /srv/tftp/openwrt-ar71xx-mikrotik-vmlinux-initramfs.elf
1231716188 server name: boothost
1231716188 next server: 192.168.1.5
1231716188 sent size: 1 option: 53 message-type 5
1231716188 sent size: 4 option: 54 server-identifier 192.168.1.5
1231716188 sent size: 4 option: 51 lease-time 12h
1231716188 sent size: 4 option: 58 T1 6h
1231716188 sent size: 4 option: 59 T2 10h30m
1231716188 sent size: 4 option: 1 netmask 255.255.255.0
1231716188 sent size: 4 option: 28 broadcast 192.168.1.255
1231716188 sent size: 4 option: 3 router 192.168.1.5
sent /srv/tftp/openwrt-ar71xx-mikrotik-vmlinux-initramfs.elf to 192.168.1.60
1231716188 available DHCP range: 192.168.1.50 -- 192.168.1.150
1231716188 vendor class: Mips_boot
Then nothing happens. What’s supposed to happen is that the router boots the initramfs file, I telnet into 192.168.1.1 (or ssh, or http), and I get into an intermediate version of OpenWRT, where I can then do the permanent install. What happens is that the router never becomes available on 192.168.1.1, and pings etc give Destination Host Unreachable.
I assume that the initramfs never boots, for some reason. This router has no serial port, so I can’t see exactly what’s failing. Does anyone have experience with this, and know what I might be doing wrong?