Despite having the ipk already downloaded, opkg wants to re-download it and fails:
root@myrouter:/tmp# pwd
/tmp
root@ myrouter:/tmp# ls -l libunbound_1.17.0-1_arm_cortex-a9_vfpv3-d16.ipk
-rw-r--r-- 1 root root 422897 Nov 25 14:15 libunbound_1.17.0-1_arm_cortex-a9_vfpv3-d16.ipk
root@ myrouter:/tmp# opkg install /tmp/libunbound_1.17.0-1_arm_cortex-a9_vfpv3-d16.ipk
Upgrading libunbound on root from 1.16.0-1 to 1.17.0-1...
Downloading https://downloads.openwrt.org/releases/21.02.3/packages/arm_cortex-a9_vfpv3-d16/packages/libunbound_1.17.0-1_arm_cortex-a9_vfpv3-d16.ipk
Collected errors:
* opkg_download: Failed to download https://downloads.openwrt.org/releases/21.02.3/packages/arm_cortex-a9_vfpv3-d16/packages/libunbound_1.17.0-1_arm_cortex-a9_vfpv3-d16.ipk, wget returned 4.
* opkg_download: Check your network settings and connectivity.
* opkg_install_pkg: Failed to download libunbound. Perhaps you need to run 'opkg update'?
* opkg_install_cmd: Cannot install package libunbound.