Facing error in POM.XML (Project build error: Non-resolvable parent POM )

I installed maven and tomcat and sts in eclipse but still facing error in POM.XML :

Multiple markers at this line

• Project build error: Non-resolvable parent POM for com.example:demo:0.0.1-SNAPSHOT: org.springframework.boot:spring-boot-starter-parent:pom:2.7.3 failed to transfer from https://repo.maven.apache.org/maven2 during a previous attempt. This failure was cached in the local repository and resolution is not reattempted until the update interval of central has elapsed or updates are forced. Original error: Could not transfer artifact org.springframework.boot:spring-boot-starter-parent:pom:2.7.3 from/to central (https://repo.maven.apache.org/maven2): Connect timed out and 'parent.relativePath' points at no local POM
• Non-resolvable parent POM for com.example:demo:0.0.1-SNAPSHOT: org.springframework.boot:spring-boot-starter-parent:pom:2.7.3 failed to transfer from https://repo.maven.apache.org/maven2 during a previous attempt. This failure was cached in the local repository and resolution is not reattempted until the update interval of central has elapsed or updates are forced. Original error: Could not transfer artifact org.springframework.boot:spring-boot-starter-parent:pom:2.7.3 from/to central (https://repo.maven.apache.org/maven2): Network is unreachable: no further information

POM.XML FILE :

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.7.3</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.example</groupId>
    <artifactId>demo</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>demo</name>
    <description>Demo project for Spring Boot</description>
    <properties>
        <java.version>1.8</java.version>
    </properties>
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

</project>