Both files are mandatory. Part 1 contains the main installer and core binaries; Part 2 contains additional components (e.g., Java, examples, advanced queueing).
Unlike the base 11.2.0.1 version, which was historically available on the public Oracle Technology Network (OTN) , the is generally only accessible through My Oracle Support (MOS) . download oracle 11.2 0.4 for linux x86-64
The checksums match. You now have the linux.x64_11gR2_database_1of2.zip and _2of2.zip files sitting in your downloads folder. Both files are mandatory