GCP Networking VPC - GCP Certification Cheat Sheet

Let’s get a quick overview of Google Cloud Networking from an GCP certification perspective. We will look at important certification questions VPC, subnets, CIDRs

You will learn

  • What is a VPC
  • Why it is important and how to set it up?
  • What is shared VPC and VPC Peering


Need for Google Cloud VPC

  • In a corporate network or an on-premises data center:
    • Can anyone on the internet see the data exchange between the application and the database?
      • No
    • Can anyone from internet directly connect to your database?
      • Typically NO.
      • You need to connect to your corporate network and then access your applications or databases.
  • Corporate network provides a secure internal network protecting your resources, data and communication from external users
  • How do you do create your own private network in the cloud?
    • Enter Virtual Private Cloud (VPC)

Google Cloud VPC (Virtual Private Cloud)

  • Your own isolated network in GCP cloud
    • Network traffic within a VPC is isolated (not visible) from all other Google Cloud VPCs
  • You control all the traffic coming in and going outside a VPC
  • (Best Practice) Create all your GCP resources (compute, storage, databases etc) within a VPC
    • Secure resources from unauthorized access AND
    • Enable secure communication between your cloud resources
  • VPC is a global resource & contains subnets in one or more region
    • (REMEMBER) NOT tied to a region or a zone. VPC resources can be in any region or zone!

Need for VPC Subnets

  • Different types of resources are created on cloud - databases, compute etc
    • Each type of resource has its own access needs
    • Load Balancers are accessible from internet (public resources)
    • Databases or VM instances should NOT be accessible from internet
      • ONLY applications within your network (VPC) should be able to access them(private resources)
  • How do you separate public resources from private resources inside a VPC?
    • Create separate Subnets!
  • (Additional Reason) You want to distribute resources across multiple regions for high availability

VPC Subnets

  • (Solution) Create different subnets for public and private resources
    • Resources in a public subnet CAN be accessed from internet
    • Resources in a private subnet CANNOT be accessed from internet
    • BUT resources in public subnet can talk to resources in private subnet
  • Each Subnet is created in a region
  • Example : VPC - demo-vpc => Subnets - region us-central1, europe-west1 or us-west1 or ..

Creating VPCs and Subnets

  • By default, every project has a default VPC
  • You can create YOUR own VPCs:
    • OPTION 1: Auto mode VPC network:
      • Subnets are automatically created in each region
      • Default VPC created automatically in the project uses auto mode!
    • OPTION 2: Custom mode VPC network:
      • No subnets are automatically created
      • You have complete control over subnets and their IP ranges
      • Recommended for Production
  • Options when you create a subnet:
    • Enable Private Google Access - Allows VM’s to connect to Google API’s using private IP’s
    • Enable FlowLogs - To troubleshoot any VPC related network issues

CIDR (Classless Inter-Domain Routing) Blocks

  • Resources in a network use continuous IP addresses to make routing easy:
    • Example: Resources inside a specific network can use IP addresses from to
  • How do you express a range of addresses that resources in a network can have?
    • CIDR block
  • A CIDR block consists of a starting IP address( and a range(/28)
    • Example: CIDR block represents addresses from to - a total of 16 addresses
  • Quick Tip: indicates that the first 28 bits (out of 32) are fixed.
    • Last 4 bits can change => 2 to the power 4 = 16 addresses

CIDR Exercises

  • Exercise : How many addresses does represent?
    • 2 to the power (32-26 = 6) = 64 addresses from to
  • Exercise : How many addresses does represent?
    • 2 to the power (32-30 = 2) = 4 addresses from to
  • Exercise : What is the difference between and
    • represent all IP addresses. represents just one IP address

  • Recommended CIDR Blocks
    • Private IP addresses RFC 1918:,,
    • Shared address space RFC 6598:
    • IETF protocol assignments RFC 6890:
  • **Restricted Range Examples **
    • You CANNOT use these as CIDR for VPC Subnets
      • Private Google Access-specific virtual IP addresses:,
      • Current (local) network RFC 1122:
      • Local host RFC 1122:
  • (REMEMBER) You CAN EXTEND the CIDR Block Range of a Subnet (Secondary CIDR Block)

Firewall Rules

  • Configure Firewall Rules to control traffic going in or out of the network:
    • Stateful
    • Each firewall rule has priority (0-65535) assigned to it
    • 0 has highest priority. 65535 has least priority
    • Default implied rule with lowest priority (65535)
      • Allow all egress
      • Deny all ingress
      • Default rules can’t be deleted
      • You can override default rules by defining new rules with priority 0-65534
    • Default VPC has 4 additional rules with priority 65534
      • Allow incoming traffic from VM instances in same network (default-allow-internal)
      • Allow Incoming TCP traffic on port 22 (SSH) default-allow-ssh
      • Allow Incoming TCP traffic on port 3389 (RDP) default-allow-rdp
      • Allow Incoming ICMP from any source on the network default-allow-icmp

Firewall Rules - Ingress and Egress Rules

  • Ingress Rules: Incoming traffic from outside to GCP targets
    • Target (defines the destination): All instances or instances with TAG/SA
    • Source (defines where the traffic is coming from): CIDR or All instances or instances with TAG/SA
  • Egress Rules: Outgoing traffic to destination from GCP targets
    • Target (defines the source): All instances or instances with TAG/SA
    • Destination: CIDR Block
  • Along with each rule, you can also define:
    • Priority - Lower the number, higher the priority
    • Action on match - Allow or Deny traffic
    • Protocol - ex. TCP or UDP or ICMP
    • Port - Which port?
    • Enforcement status - Enable or Disable the rule

Shared VPC

  • Scenario: Your organization has multiple projects. You want resources in different projects to talk to each other?
    • How to allow resources in different projects to talk with internal IPs securely and efficiently?
  • Enter Shared VPC
    • Created at organization or shared folder level (Access Needed: Shared VPC Admin)
    • Allows VPC network to be shared between projects in same organization
    • Shared VPC contains one host project and multiple service projects:
      • Host Project - Contains shared VPC network
      • Service Projects - Attached to host projects
  • Helps you achieve separation of concerns:
    • Network administrators responsible for Host projects and Resource users use Service Project

VPC Peering

  • Scenario: How to connect VPC networks across different organizations?
  • Enter VPC Peering
    • Networks in same project, different projects and across projects in different organizations can be peered
    • All communication happens using internal IP addresses
      • Highly efficient because all communication happens inside Google network
      • Highly secure because not accessible from Internet
      • No data transfer charges for data transfer between services
    • (REMEMBER) Network administration is NOT changed:
      • Admin of one VPC do not get the role automatically in a peered network

Certification - Recommended Reading

Cloud Certifications - AWS, Azure and Google Cloud - Top 8 FAQ For Me

Google Cloud For Beginners - How to choose a Database Service?

Teaching Cloud Certifications - Top 6 Learnings

Google Cloud For Beginners - How to choose a Compute Service?

Important Kubernetes Concepts Made Easy

Introduction to Google Cloud - For AWS Professionals

Getting Started with Docker - 5 Easy Steps

GCP PubSub - GCP Certification Cheat Sheet

GCP IAM - GCP Certification Cheat Sheet

GCP App Engine - GCP Certification Cheat Sheet


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