Add or remove a CIDR block from your VPC - Amazon Virtual Private Cloud

Add or remove a CIDR block from your VPC

This section describes how to add or remove IPv4 and IPv6 CIDR blocks from a VPC.

Important

  • Your VPC can have up to five IPv4 and five IPv6 CIDR blocks by default, but this limit is adjustable. For more information, see Amazon VPC quotas. For information about restrictions on CIDR blocks for a VPC, see VPC CIDR blocks.

  • If your VPC has more than one IPv4 CIDR block associated with it, you can remove an IPv4 CIDR block from the VPC. You cannot remove the primary IPv4 CIDR block. You must remove an entire CIDR block; you cannot remove a subset of a CIDR block or a merged range of CIDR blocks. You must first delete all subnets in the CIDR block.

  • If you no longer want IPv6 support in your VPC, but you want to continue using your VPC to create and communicate with IPv4 resources, you can remove the IPv6 CIDR block.

  • To remove an IPv6 CIDR block, you must first unassign any IPv6 addresses that are assigned to any instances in your subnet.

  • Removing an IPv6 CIDR block does not automatically delete any security group rules, network ACL rules, or route table routes that you've configured for IPv6 networking. You must manually modify or delete these rules or routes.

To add or remove a CIDR block from a VPC using the console

  1. Open the Amazon VPC console at https://console.aws.amazon.com/vpc/.

  2. In the navigation pane, choose Your VPCs.

  3. Select the VPC, and then choose Actions, Edit CIDRs.

  4. To remove a CIDR, choose Remove next to the CIDR.

  5. To add a CIDR, choose Add new IPv4 CIDR or Add new IPv6 CIDR.

  6. To add a CIDR for IPv4 CIDR block, do one of the following:

    • Choose IPv4 CIDR manual input and enter an IPv4 CIDR block.

    • Choose IPAM-allocated IPv4 CIDR and select a CIDR from an IPv4 IPAM pool.

    • Choose Save.

  7. To add a CIDR for IPv6 CIDR block, do the following:

    • Choose IPAM-allocated IPv6 CIDR block if you are using Amazon VPC IP Address Manager and you want to provision a IPv6 CIDR from an IPAM pool. You have two options for provisioning an IP address range to the VPC under CIDR block:

      • Netmask length: Choose this option to select a netmask length for the CIDR. Do one of the following:

        • If there is a default netmask length selected for the IPAM pool, you can choose Default to IPAM netmask length to use the default netmask length set for the IPAM pool by the IPAM administrator. For more information about the optional default netmask length allocation rule, see Create a Regional IPv6 pool in the Amazon VPC IPAM User Guide.

        • If there is no default netmask length selected for the IPAM pool, choose a netmask length that's more specific than the netmask length of the IPAM pool CIDR. For example, if the IPAM pool CIDR is /50, you can choose a netmask length between /52 to /60 for the VPC. Possible netmask lengths are between /44 and /60 in increments of /4.

      • Select a CIDR: Choose this option to manually enter an IPv6 address. You can only choose a netmask length that's more specific than the netmask length of the IPAM pool CIDR. For example, if the IPAM pool CIDR is /50, you can choose a netmask length between /52 to /60 for the VPC. Possible IPv6 netmask lengths are between /44 and /60 in increments of /4.

    • Choose Amazon-provided IPv6 CIDR block to request an IPv6 CIDR block from an Amazon pool of IPv6 addresses. For Network Border Group, select the group from which AWS advertises IP addresses. Amazon provides a fixed IPv6 CIDR block size of /56.

    • Choose IPv6 CIDR owned by me to provision an IPv6 CIDR that you have already brought to AWS. For more information about bringing your own IP address ranges to AWS, see Bring your own IP addresses (BYOIP) in Amazon EC2 in the Amazon EC2 User Guide. You have two options for provisioning an IP address range to the VPC under CIDR block:

      • No preference: Choose this option to use netmask length of /56.

      • Select a CIDR: Choose this option to manually enter an IPv6 address and choose a netmask length that's more specific than the size of BYOIP CIDR. For example, if the BYOIP pool CIDR is /50, you can choose a netmask length between /52 to /60 for the VPC. Possible IPv6 netmask lengths are between /44 and /60 in increments of /4.

      • Choose Select CIDR when you're done.

  8. Choose Close.

  9. If you've added a CIDR block to your VPC, you can create subnets that use the new CIDR block. For more information, see Create a subnet.

To associate or disassociate a CIDR block from a VPC using the AWS CLI

Use the associate-vpc-cidr-block and disassociate-vpc-cidr-block commands.