I have tried it also with scp transferred ipk file:
root@OpenWrt:/tmp# opkg install nmap_7.80-3_arm_cortex-a15_neon-vfpv4.ipk
Unknown package 'nmap'.
Collected errors:
* pkg_hash_fetch_best_installation_candidate: Packages for nmap found, but incompatible with the architectures configured
* opkg_install_cmd: Cannot install package nmap.
I have also commented out feed in distfeeds.conf and added my repo into customfeeds.conf:
root@OpenWrt:/tmp# cat /etc/opkg/distfeeds.conf
#src/gz openwrt_core https://downloads.openwrt.org/snapshots/targets/ipq806x/generic/packages
#src/gz openwrt_base https://downloads.openwrt.org/snapshots/packages/arm_cortex-a15_neon-vfpv4/base
#src/gz openwrt_freifunk https://downloads.openwrt.org/snapshots/packages/arm_cortex-a15_neon-vfpv4/freifunk
#src/gz openwrt_luci https://downloads.openwrt.org/snapshots/packages/arm_cortex-a15_neon-vfpv4/luci
#src/gz openwrt_packages https://downloads.openwrt.org/snapshots/packages/arm_cortex-a15_neon-vfpv4/packages
#src/gz openwrt_routing https://downloads.openwrt.org/snapshots/packages/arm_cortex-a15_neon-vfpv4/routing
#src/gz openwrt_telephony https://downloads.openwrt.org/snapshots/packages/arm_cortex-a15_neon-vfpv4/telephony
root@OpenWrt:/tmp# cat /etc/opkg/customfeeds.conf
# add your custom package feeds here
#
# src/gz example_feed_name http://www.example.com/path/to/files
src/gz local http://192.168.1.10/openwrt/packages
I am not sure if it is important for this discussion because problem seems to be arch mismatch. Although arch seems to be the same to me. Unfortunately opkg doesn't list accepted/provided archs directly in error message so I can only guess that accepted are the ones listed in "opkg print-architecture" and provided in "opkg info nmap". I have also verified that control file in nmap-full_7.80-3_arm_cortex-a15_neon-vfpv4.ipk contains the same arch:
Package: nmap
Version: 7.80-3
Depends: libc, libpcap1, libstdcpp6, zlib, libpcre
Source: feeds/packages/net/nmap
SourceName: nmap
License: GPL-2.0-only
LicenseFiles: COPYING
Section: net
SourceDateEpoch: 1591173083
CPE-ID: cpe:/a:nmap:nmap
Maintainer: Nuno Goncalves <nunojpg@gmail.com>
Architecture: arm_cortex-a15_neon-vfpv4
Installed-Size: 2246450
Description: Utility for network exploration or security auditing