While setting a D-Bus property using busctl it throws the error message
"The operation is not allowed". 
busctl introspect xyz.openbmc_project.Network /xyz/openbmc_project/network/eth1/ipv6/f8ea20e3 xyz.openb
mc_project.Network.IP
NAME                           TYPE      SIGNATURE RESULT/VALUE                             FLAGS
.Address                       property  s         "fe80::7036:4aff:fed7:9897"              emits-change writable
.Gateway                       property  s         ""                                       emits-change writable
.Origin                        property  s         "xyz.openbmc_project.Network.IP.Addre... emits-change writable
.PrefixLength                  property  y         64                                       emits-change writable
.Type                          property  s         "xyz.openbmc_project.Network.IP.Proto... emits-change writable
busctl --verbose set-property xyz.openbmc_project.Network /xyz/openbmc_project/network/eth1/ipv6/f8ea20
e3 xyz.openbmc_project.Network.IP Gateway s "fe80::7036:4aff:fed7:9897"
Failed to set property Gateway on interface xyz.openbmc_project.Network.IP: The operation is not allowed