code: func IsValid(na *wire.NetAddress) bool {
  	// IsUnspecified returns if address is 0, so only all bits set, and
  	// RFC3849 need to be explicitly checked.
  	return na.IP != nil && !(na.IP.IsUnspecified() ||
  		na.IP.Equal(net.IPv4bcast))
  }
docs: // IsValid returns whether or not the passed address is valid.  The address is
  // considered invalid under the following circumstances:
  // IPv4: It is either a zero or all bits set address.
  // IPv6: It is either a zero or RFC3849 documentation address.