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AWScloud~5 mins

Route tables configuration in AWS - Cheat Sheet & Quick Revision

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Recall & Review
beginner
What is a route table in AWS?
A route table in AWS is a set of rules, called routes, that determine where network traffic from your subnet or gateway is directed.
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beginner
How do you associate a route table with a subnet?
You associate a route table with a subnet by specifying the subnet in the route table's associations. This controls the routing for that subnet's traffic.
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intermediate
What is the purpose of a default route (0.0.0.0/0) in a route table?
A default route (0.0.0.0/0) sends all traffic destined for addresses not explicitly listed in the route table to a specified target, like an internet gateway, enabling internet access.
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intermediate
Can a subnet be associated with multiple route tables at the same time?
No, a subnet can only be associated with one route table at a time. This ensures clear routing rules for that subnet.
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beginner
What happens if a route table has no route for a destination IP?
If a route table has no route for a destination IP, the traffic is dropped because AWS does not know where to send it.
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What does a route table control in AWS?
AStorage allocation
BUser permissions
CCPU usage
DWhere network traffic is directed
Which target is commonly used in a route for internet access?
AInternet Gateway
BVirtual Private Gateway
CElastic Load Balancer
DSecurity Group
Can a subnet have multiple route tables associated simultaneously?
ANo, only one
BYes, always
COnly in VPC peering
DOnly for public subnets
What does the route destination 0.0.0.0/0 represent?
ALocal network only
BAll IPv4 addresses
CIPv6 addresses
DPrivate IP addresses
What happens if no route matches the destination IP in a route table?
ATraffic is sent to the internet
BTraffic is sent to the default subnet
CTraffic is dropped
DTraffic is logged and retried
Explain how route tables control network traffic in an AWS VPC.
Think about how traffic knows where to go inside and outside the VPC.
You got /4 concepts.
    Describe the role of the default route 0.0.0.0/0 in a route table and when you would use it.
    Consider what happens when traffic is destined for an unknown IP.
    You got /3 concepts.

      Practice

      (1/5)
      1. What is the main purpose of a route table in AWS networking?
      easy
      A. To manage user permissions
      B. To store user data securely
      C. To direct network traffic between subnets and gateways
      D. To monitor server health

      Solution

      1. Step 1: Understand the role of route tables

        Route tables control how network traffic moves inside a cloud network by defining paths.

      2. Step 2: Identify what route tables connect

        They connect subnets to gateways or other networks, enabling communication.

      3. Final Answer:

        To direct network traffic between subnets and gateways -> Option C

      4. Quick Check:

        Route tables = traffic direction [OK]
      Hint: Route tables guide traffic flow inside the cloud [OK]
      Common Mistakes:
      • Confusing route tables with security groups
      • Thinking route tables store data
      • Mixing route tables with monitoring tools
      2. Which of the following is the correct way to associate a route table with a subnet in AWS CLI?
      easy
      A. aws ec2 create-route-table --subnet-id subnet-12345 --route-table-id rtb-67890
      B. aws ec2 associate-route-table --subnet-id subnet-12345 --route-table-id rtb-67890
      C. aws ec2 attach-route-table --subnet subnet-12345 --table rtb-67890
      D. aws ec2 link-route-table --subnet subnet-12345 --route-table rtb-67890

      Solution

      1. Step 1: Identify the correct AWS CLI command for association

        The command to associate a route table with a subnet is 'associate-route-table'.

      2. Step 2: Check the correct syntax and parameters

        The correct syntax uses '--subnet-id' and '--route-table-id' flags with IDs.

      3. Final Answer:

        aws ec2 associate-route-table --subnet-id subnet-12345 --route-table-id rtb-67890 -> Option B

      4. Quick Check:

        Associate route table = associate-route-table command [OK]
      Hint: Use 'associate-route-table' with subnet and route table IDs [OK]
      Common Mistakes:
      • Using 'create-route-table' instead of 'associate-route-table'
      • Wrong parameter names like '--subnet' instead of '--subnet-id'
      • Using non-existent commands like 'attach-route-table'
      3. Given a route table with the following routes:
      Destination: 0.0.0.0/0, Target: igw-12345
      Destination: 10.0.1.0/24, Target: local
      What happens when an instance in subnet 10.0.1.0/24 tries to reach 8.8.8.8?
      medium
      A. Traffic is sent to the internet gateway (igw-12345)
      B. Traffic is blocked because no route exists
      C. Traffic is sent to the local subnet only
      D. Traffic is sent to a NAT gateway automatically

      Solution

      1. Step 1: Analyze the route for 0.0.0.0/0

        This route sends all traffic not matching other routes to the internet gateway (igw-12345).

      2. Step 2: Determine route for 8.8.8.8

        Since 8.8.8.8 is outside the local subnet, it matches the 0.0.0.0/0 route and goes to the internet gateway.

      3. Final Answer:

        Traffic is sent to the internet gateway (igw-12345) -> Option A

      4. Quick Check:

        Default route sends traffic to internet gateway [OK]
      Hint: Default 0.0.0.0/0 route sends traffic outside subnet [OK]
      Common Mistakes:
      • Assuming traffic is blocked without explicit deny
      • Confusing local route with internet access
      • Thinking NAT gateway is used without configuration
      4. You created a route table and associated it with a subnet, but instances in that subnet cannot access the internet. What is the most likely mistake?
      medium
      A. The route table lacks a route to an internet gateway
      B. The subnet is not associated with any route table
      C. The route table has a route to a NAT gateway instead of an internet gateway
      D. The instances have no security group attached

      Solution

      1. Step 1: Check route table routes for internet access

        Internet access requires a route to an internet gateway (igw) for 0.0.0.0/0.

      2. Step 2: Identify missing or incorrect routes

        If the route to the internet gateway is missing, instances cannot reach the internet despite association.

      3. Final Answer:

        The route table lacks a route to an internet gateway -> Option A

      4. Quick Check:

        Internet needs 0.0.0.0/0 route to igw [OK]
      Hint: Check for 0.0.0.0/0 route to internet gateway [OK]
      Common Mistakes:
      • Assuming subnet association alone grants internet access
      • Confusing NAT gateway with internet gateway routes
      • Ignoring security group rules as cause
      5. You have two subnets: Subnet A (10.0.1.0/24) and Subnet B (10.0.2.0/24). You want instances in Subnet A to access the internet via a NAT gateway in Subnet B, but Subnet B should not have direct internet access. How should you configure the route tables?
      hard
      A. Associate Subnet A's route table with 0.0.0.0/0 to the NAT gateway; Subnet B's route table with no route to internet gateway
      B. Associate Subnet A's route table with 0.0.0.0/0 to the internet gateway; Subnet B's route table with 0.0.0.0/0 to the NAT gateway
      C. Associate both subnets' route tables with 0.0.0.0/0 to the internet gateway
      D. Associate Subnet A's route table with a route 0.0.0.0/0 to the NAT gateway; Subnet B's route table with 0.0.0.0/0 to the internet gateway

      Solution

      1. Step 1: Understand NAT gateway purpose

        NAT gateway allows instances in private subnet (Subnet A) to access internet outbound.

      2. Step 2: Configure Subnet B's route table (NAT subnet)

        Subnet B must have 0.0.0.0/0 to internet gateway so NAT can reach internet. Direct access for instances in B can be restricted via security groups.

      3. Step 3: Configure Subnet A's route table

        Subnet A has 0.0.0.0/0 to NAT gateway.

      4. Final Answer:

        Associate Subnet A's route table with a route 0.0.0.0/0 to the NAT gateway; Subnet B's route table with 0.0.0.0/0 to the internet gateway -> Option D

      5. Quick Check:

        Private to NAT; NAT subnet to igw [OK]
      Hint: Private subnet (A) routes to NAT; NAT subnet (B) routes to igw [OK]
      Common Mistakes:
      • Omitting igw route in NAT subnet (B), breaking NAT functionality
      • Routing private subnet (A) directly to igw
      • Confusing NAT gateway and internet gateway roles