Which aws service or component allows inbound traffic from the internet to access a vpc?
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A network access control list (ACL) allows or denies specific inbound or outbound traffic at the subnet level. You can use the default network ACL for your VPC, or you can create a custom network ACL for your VPC with rules that are similar to the rules for your security groups in order to add an additional layer of security to your VPC. Show
The following diagram shows a VPC with two subnets. Each subnet has a network ACL. When traffic enters the VPC (for example, from a peered VPCs, VPN connection, or the internet), the router sends the traffic to its destination. Network ACL A determines which traffic destined for subnet 1 is allowed to enter subnet 1, and which traffic destined for a location outside subnet 1 is allowed to leave subnet 1. Similarly, network ACL B determines which traffic is allowed to enter and leave subnet 2. For more information about the differences between security groups and network ACLs, see Compare security groups and network ACLs. Contents
Network ACL basicsThe following are the basic things that you need to know about network ACLs:
There are quotas (also known as limits) for the number of network ACLs per VPC and the number of rules per network ACL. For more information, see Amazon VPC quotas. Network ACL rulesYou can add or remove rules from the default network ACL, or create additional network ACLs for your VPC. When you add or remove rules from a network ACL, the changes are automatically applied to the subnets that it's associated with. The following are the parts of a network ACL rule:
If you add a rule using a command line tool or the Amazon EC2 API, the CIDR range is automatically modified to its canonical form. For example, if you specify Default network ACLThe default network ACL is configured to allow all traffic to flow in and out of the subnets with which it is associated. Each network ACL also includes a rule whose rule number is an asterisk. This rule ensures that if a packet doesn't match any of the other numbered rules, it's denied. You can't modify or remove this rule. The following is an example default network ACL for a VPC that supports IPv4 only.
If you create a VPC with an IPv6 CIDR block or if you associate an IPv6 CIDR block with your existing VPC, we automatically add rules that allow all IPv6 traffic to flow in and out of your subnet. We also add rules whose rule numbers are an asterisk that ensures that a packet is denied if it doesn't match any of the other numbered rules. You can't modify or remove these rules. The following is an example default network ACL for a VPC that supports IPv4 and IPv6. If you've modified your default network ACL's inbound rules, we do not automatically add an allow rule for inbound IPv6 traffic when you associate an IPv6 block with your VPC. Similarly, if you've modified the outbound rules, we do not automatically add an allow rule for outbound IPv6 traffic.
Custom network ACLThe following table shows an example of a custom network ACL for a VPC that supports IPv4 only. It includes rules that allow HTTP and HTTPS traffic in (inbound rules 100 and 110). There's a corresponding outbound rule that enables responses to that inbound traffic (outbound rule 140, which covers ephemeral ports 32768-65535). For more information about how to select the appropriate ephemeral port range, see Ephemeral ports. The network ACL also includes inbound rules that allow SSH and RDP traffic into the subnet. The outbound rule 120 enables responses to leave the subnet. The network ACL has outbound rules (100 and 110) that allow outbound HTTP and HTTPS traffic out of the subnet. There's a corresponding inbound rule that enables responses to that outbound traffic (inbound rule 140, which covers ephemeral ports 32768-65535). Each network ACL includes a default rule whose rule number is an asterisk. This rule ensures that if a packet doesn't match any of the other rules, it's denied. You can't modify or remove this rule.
As a packet comes to the subnet, we evaluate it against the inbound rules of the ACL that the subnet is associated with (starting at the top of the list of rules, and moving to the bottom). Here's how the evaluation goes if the packet is destined for the HTTPS port (443). The packet doesn't match the first rule evaluated (rule 100). It does match the second rule (110), which allows the packet into the subnet. If the packet had been destined for port 139 (NetBIOS), it doesn't match any of the rules, and the * rule ultimately denies the packet. You might want to add a deny rule in a situation where you legitimately need to open a wide range of ports, but there are certain ports within the range that you want to deny. Just make sure to place the deny rule earlier in the table than the rule that allows the wide range of port traffic. You add allow rules depending on your use case. For example, you can add a rule that allows outbound TCP and UDP access on port 53 for DNS resolution. For every rule that you add, ensure that there is a corresponding inbound or outbound rule that allows response traffic. The following table shows the same example of a custom network ACL for a VPC that has an associated IPv6 CIDR block. This network ACL includes rules for all IPv6 HTTP and HTTPS traffic. In this case, new rules were inserted between the existing rules for IPv4 traffic. You can also add the rules as higher number rules after the IPv4 rules. IPv4 and IPv6 traffic are separate, and therefore none of the rules for the IPv4 traffic apply to the IPv6 traffic.
For more examples, see Recommended rules for VPC scenarios. Custom network ACLs and other AWS servicesIf you create a custom network ACL, be aware of how it might affect resources that you create using other AWS services. With Elastic Load Balancing, if the subnet for your backend instances has a
network ACL in which you've added a deny rule for all traffic with a source of either Ephemeral portsThe example network ACL in the preceding section uses an ephemeral port range of 32768-65535. However, you might want to use a different range for your network ACLs depending on the type of client that you're using or with which you're communicating. The client that initiates the request chooses the ephemeral port range. The range varies depending on the client's operating system.
For example, if a request comes into a web server in your VPC from a Windows 10 client on the internet, your network ACL must have an outbound rule to enable traffic destined for ports 49152-65535. If an instance in your VPC is the client initiating a request, your network ACL must have an inbound rule to enable traffic destined for the ephemeral ports specific to the type of instance (Amazon Linux, Windows Server 2008, and so on). In practice, to cover the different types of clients that might initiate traffic to public-facing instances in your VPC, you can open ephemeral ports 1024-65535. However, you can also add rules to the ACL to deny traffic on any malicious ports within that range. Ensure that you place the deny rules earlier in the table than the allow rules that open the wide range of ephemeral ports. Path MTU DiscoveryPath MTU Discovery is used to determine the path MTU between two devices. The path MTU is the maximum packet size that's supported on the path between the originating host and the receiving host. For IPv4, when a host sends a packet that's larger than the MTU of the receiving host or that's larger than the MTU of a device along the path, the receiving host or device drops the packet, and then returns the following ICMP message: The IPv6
protocol does not support fragmentation in the network. When a host sends a packet that's larger than the MTU of the receiving host or that's larger than the MTU of a device along the path, the receiving host or device drops the packet, and then returns the following ICMP message: If the maximum transmission unit (MTU) between hosts in your subnets is different, or your instances communicate with peers over the internet, you must add the following network ACL rule, both inbound and outbound. This ensures that Path MTU Discovery can function correctly and prevent packet loss. Select Custom ICMP Rule for the type and Destination Unreachable, fragmentation required, and DF flag set for the port range (type 3, code 4). If you use traceroute, also add the following rule: select Custom ICMP Rule for the type and Time Exceeded, TTL expired transit for the port range (type 11, code 0). For more information, see Network maximum transmission unit (MTU) for your EC2 instance in the Amazon EC2 User Guide for Linux Instances. Work with network ACLsThe following tasks show you how to work with network ACLs using the Amazon VPC console. Tasks
Determine network ACL associationsYou can use the Amazon VPC console to determine the network ACL that's associated with a subnet. Network ACLs can be associated with more than one subnet, so you can also determine which subnets are associated with a network ACL. To determine which network ACL is associated with a subnet
To determine which subnets are associated with a network ACL
Create a network ACLYou can create a custom network ACL for your VPC. By default, a network ACL that you create blocks all inbound and outbound traffic until you add rules, and is not associated with a subnet until you explicitly associate it with one. To create a network ACL
Add and delete rulesWhen you add or delete a rule from an ACL, any subnets that are associated with the ACL are subject to the change. You don't have to terminate and relaunch the instances in the subnet. The changes take effect after a short period. Be very careful if you are adding and deleting rules at the same time. Network ACL rules define which types of network traffic can enter or exit your VPCs. If you delete inbound or outbound rules and then add more new entries than are allowed in Amazon VPC quotas, the entries selected for deletion will be removed and new entries will not be added. This could cause unexpected connectivity issues and unintentionally prevent access to and from your VPCs. If you're using the Amazon EC2 API or a command line tool, you can't modify rules. You can only add and delete rules. If you're using the Amazon VPC console, you can modify the entries for existing rules. The console removes the existing rule and adds a new rule for you. If you need to change the order of a rule in the ACL, you must add a new rule with the new rule number, and then delete the original rule. To add rules to a network ACL
To delete a rule from a network ACL
Associate a subnet with a network ACLTo apply the rules of a network ACL to a particular subnet, you must associate the subnet with the network ACL. You can associate a network ACL with multiple subnets. However, a subnet can be associated with only one network ACL. Any subnet that is not associated with a particular ACL is associated with the default network ACL by default. To associate a subnet with a network ACL
Disassociate a network ACL from a subnetYou can disassociate a custom network ACL from a subnet. When the subnet has been disassociated from the custom network ACL, it is then automatically associated with the default network ACL. To disassociate a subnet from a network ACL
Change a subnet's network ACLYou can change the network ACL that's associated with a subnet. For example, when you create a subnet, it is initially associated with the default network ACL. You might want to instead associate it with a custom network ACL that you've created. After changing a subnet's network ACL, you don't have to terminate and relaunch the instances in the subnet. The changes take effect after a short period. To change a subnet's network ACL association
Delete a network ACLYou can delete a network ACL only if there are no subnets associated with it. You can't delete the default network ACL. To delete a network ACL
API and command overviewYou can perform the tasks described on this page using the command line or an API. For more information about the command line interfaces and a list of available APIs, see Working with Amazon VPC. Example: Control access to instances in a subnetIn this example, instances in your subnet can communicate with each other, and are accessible from a trusted remote computer. The remote computer might be a computer in your local network or an instance in a different subnet or VPC. You use it to connect to your instances to perform administrative tasks. Your security group rules and network ACL rules allow access from the IP address of your remote computer (172.31.1.2/32). All other traffic from the internet or other networks is denied. This scenario gives you the flexibility to change the security groups or security group rules for your instances, and have the network ACL as the backup layer of defense.  The following is an example security group to associate with the instances. Security groups are stateful. Therefore you don't need a rule that allows responses to inbound traffic.
The following is an example network ACL to associate with the subnets for the instances. The network ACL rules apply to all instances in the subnet. Network ACLs are stateless. Therefore, you need a rule that allows responses to inbound traffic.
If you accidentally make your security group rules too permissive, the network ACL in this example continues to permit access only from the specified IP address. For example, the following security group contains a rule that allow inbound SSH access from any IP address. However, if you associate this security group with an instance in a subnet that uses the network ACL, only other instances within the subnet and your remote computer can access the instance, because the network ACL rules deny other inbound traffic to the subnet.
Recommended rules for VPC scenariosYou can follow the processes in Scenarios to implement common scenarios for Amazon VPC. Each scenario in that section includes recommended network ACL rules. If you implement these scenarios as described in the documentation, you use the default network access control list (ACL) which allows all inbound and outbound traffic. If you need an additional layer of security, you can create a network ACL and add rules. Which AWS service or feature allows a user to establish a dedicated network connection between a company's onAWS Direct Connect makes it easy to establish a dedicated connection from an on-premises network to one or more VPCs in the same region.
Which AWS feature or service can be used to capture information about incoming and outgoing traffic in an AWS VPC infrastructure?Flow logs: Flow logs capture information about the IP traffic going to and from network interfaces in your VPC. You can create a flow log for a VPC, subnet, or individual network interface.
Which AWS service or feature allows a user to easily scale connectivity among thousands of VPCs?AWS Transit Gateway allows you to easily scale connectivity across thousands of Amazon VPCs, AWS accounts, and on-premises networks controls.
Which AWS service allows companies to connect an Amazon VPC to an onAWS Direct Connect enables you to securely connect your AWS environment to your on-premises data center or office location over a standard 1 gigabit or 10 gigabit Ethernet fiber-optic connection.
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