https://software.cisco.com/download/home/286313172/type/280805694/release/7.4.2
NCS5500-docs-7.4.2.tar
NCS5500-iosxr-7.4.2.tar
NCS5500-iosxr-k9-7.4.2.tar
ncs5500-usb_boot-7.4.2.zip