Hi, yum update and its successor dnf update require internet connection to access repositories.
Generic instruction for getting and installing packages on Fedora without internet connection
It's a bit easier if you have other Fedora system with internet access, then you can download all packages using sudo dnf install --downloadonly --downloaddir=/path_where_to_save_files/ package1 package2. You can also use it to check dependencies using sudo dnf repoquery --requires --resolve package_name, but that way you'll also get some packages already available on an offline system hence not necessary do download.
If you already have .rpm packages downloaded, navigate terminal to the folder with those files and use sudo dnf install --disablerepo=* *.rpm or sudo dnf install --disablerepo=* /full_path_to_folder/*.rpm run from any location. dnf will tell you if you need any other packages as dependencies - then download them, put into folder with the rest of .rpm files and try again.
For anyone interested, I got below list of links by using:
dnf repoquery --location --latest-limit=1 --arch=x86_64,noarch broadcom-wl akmod-wl akmods binutils cpp dwz elfutils-libelf-devel fakeroot fakeroot-libs fedora-rpm-macros fpc-srpm-macros gcc ghc-srpm-macros glibc-devel glibc-headers gnat-srpm-macros go-srpm-macros isl kernel-devel kernel-headers kmodtool nim-srpm-macros ocaml-srpm-macros openblas-srpm-macros patch perl-srpm-macros python-srpm-macros qt5-srpm-macros redhat-rpm-config rpm-build rpmdevtools rust-srpm-macros xemacs-filesystem zlib-devel zstd kernel kernel-core kernel-modules kernel-modules-extra
and list of packages by trying to install broadcom-wl on live-booted Fedora 27 - if someone has a better way of getting it (without omitting anything that's been already installed on my system), please let me know. I couldn't get dnf repoquery to do it, some options from docs just didn't work. I wonder if anyone reads this and responds...
Sorry for the delay. You're installing wrong package.
Manual instruction for this specific case (broadcom-wl)
Download (any download manager should be able to get all files at once) and install (using command I posted before) undermentioned 39 packages:
http://ftp.icm.edu.pl/pub/Linux/distributions/rpmfusion/nonfree/fedora/updates/27/x86_64/a/akmod-wl-6.30.223.271-16.fc27.x86_64.rpm
http://mirror.karneval.cz/pub/linux/fedora/linux/releases/27/Everything/x86_64/os/Packages/d/dwz-0.12-5.fc27.x86_64.rpm
http://mirror.karneval.cz/pub/linux/fedora/linux/releases/27/Everything/x86_64/os/Packages/f/fakeroot-1.22-1.fc27.x86_64.rpm
http://mirror.karneval.cz/pub/linux/fedora/linux/releases/27/Everything/x86_64/os/Packages/f/fakeroot-libs-1.22-1.fc27.x86_64.rpm
http://mirror.karneval.cz/pub/linux/fedora/linux/releases/27/Everything/x86_64/os/Packages/f/fedora-rpm-macros-26-3.fc27.noarch.rpm
http://mirror.karneval.cz/pub/linux/fedora/linux/releases/27/Everything/x86_64/os/Packages/f/fpc-srpm-macros-1.1-3.fc27.noarch.rpm
http://mirror.karneval.cz/pub/linux/fedora/linux/releases/27/Everything/x86_64/os/Packages/g/ghc-srpm-macros-1.4.2-6.fc27.noarch.rpm
http://mirror.karneval.cz/pub/linux/fedora/linux/releases/27/Everything/x86_64/os/Packages/g/gnat-srpm-macros-4-4.fc27.noarch.rpm
http://mirror.karneval.cz/pub/linux/fedora/linux/releases/27/Everything/x86_64/os/Packages/i/isl-0.16.1-3.fc27.x86_64.rpm
http://mirror.karneval.cz/pub/linux/fedora/linux/releases ...
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