RAR archive of 3.47 MB labelled WAG120N with the number 1.7, which most likely refers to a firmware or document version for that Linksys modem router model. The name does not say whether the contents are firmware images, a schematic or service notes, so open the archive and inspect each file before use. If it holds firmware, confirm the hardware version printed on the device label matches, since flashing an image for a different hardware revision can leave the router unbootable and needing serial or JTAG recovery.
The button opens the matching file on RM Schematics, or a source page if it is not catalogued there yet. The original attachment is from @biositechyangiyer. Enginerys does not host this file.
How to open a .rar file
Compressed archive — the usual wrapper for a schematic + boardview pair or a BIOS + EC set.