For openSUSE Tumbleweed run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:seife:testing/openSUSE_Tumbleweed/home:seife:testing.repo
zypper refresh
zypper install arpwatch-ethercodes
For openSUSE Factory run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:seife:testing/openSUSE_Factory/home:seife:testing.repo
zypper refresh
zypper install arpwatch-ethercodes
For 15.6 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:seife:testing/15.6/home:seife:testing.repo
zypper refresh
zypper install arpwatch-ethercodes
For 15.5 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:seife:testing/15.5/home:seife:testing.repo
zypper refresh
zypper install arpwatch-ethercodes