Core network policy parameters - AWS Network Manager

Core network policy parameters

The following sections describe the parameters that you use to create a core network policy version using JSON. Your JSON file contains two sections that describe the policy network settings and segments. You can then add two optional sections for defining segment actions and attachment policies.

For example JSON policies, see Core network policy examples.


The core network configuration section defines the Regions where a core network should operate.

For AWS Regions that are defined in the policy, the core network creates a Core Network Edge where you can connect attachments. After it's created, each Core Network Edge is peered with every other defined Region and is configured with consistent segment and routing across all Regions. Regions can't be removed until the associated attachments are deleted. core-network-configuration is required.


The following parameters are used in core-network-configuration:

  • asn-ranges — The Autonomous System Numbers (ASNs) to assign to Core Network Edges. By default, the core network automatically assigns an ASN for each Core Network Edge, but you can optionally define the ASN in the edge-locations for each Region. The ASN uses an array of integer ranges only from 64512 to 65534 and 4200000000 to 4294967294. No other ASN ranges can be used.

    For example, you might have the following:

    "asn-ranges": [ "64512-65534", "4200000000-4294967294" ],
  • inside-cidr-blocks — (Optional) The Classless Inter-Domain Routing (CIDR) block range used to create tunnels for AWS Transit Gateway Connect. The format is standard AWS CIDR range (for example, You can optionally define the inside CIDR in the Core Network Edges section per Region. The minimum is a /24 for IPv4 or /64 for IPv6. You can provide multiple /24 subnets or a larger CIDR range. If you define a larger CIDR range, new Core Network Edges will be automatically assigned /24 and /64 subnets from the larger CIDR. an Inside CIDR block is required for attaching Connect attachments to a Core Network Edge.

  • vpn-ecmp-support — (Optional) Indicate whether the core network forwards traffic over multiple equal-cost routes using VPN. The value can either be true or false. The default is true.

  • edge-locations — An array of AWS Region locations where you're creating Core Network Edges. The array is composed of the following parameters:

    • location — An AWS Region code, such as us-east-1.

    • asn — (Optional) The ASN of the Core Network Edge in an AWS Region. By default, the ASN will be a single integer automatically assigned from asn-ranges.


      You can't change the ASN of a Core Network Edge. Any transit gateway with the same ASN can't be peered to that Core Network Edge. For example, if you have a Core Network Edge with an ASN of 64512, you can't peer any transit gateway that also has an ASN of 64512.

    • inside-cidr-blocks — (Optional) The local CIDR blocks for this Core Network Edge for AWS Transit Gateway Connect attachments. By default, this CIDR block will be one or more optional IPv4 and IPv6 CIDR prefixes auto-assigned from inside-cidr-blocks.


The segments section defines the different segments in the network. Here you can provide descriptions, change defaults, and provide explicit regional, operational, and route filters. The names defined for each segment are used in the segment-actions and attachment-policies section. Each segment is created and operates as a completely separate routing domain. By default, attachments can only communicate with other attachments in the same segment. segments is a required section.


The following parameters are used in segments:

  • segments — At least one segment must be defined and composed of the following parameters:

    • name — The name of the segment. The name is a string used in other parts of the policy document, as well as in the console for metrics and other reference points. Valid characters are a–z, A–Z, and 0–9.


      There is no ARN or ID for a segment.

    • description — (Optional) A user-defined string describing the segment.

    • edge-locations — (Optional) Allows you to define a more restrictive set of Regions for a segment. The edge location must be a subset of the locations that are defined for edge-locations in the core-network-configuration. These locations use the AWS Region code. For example, you might want to use us-east-1 as an edge location.

    • isolate-attachments — (Optional) This Boolean setting determines whether attachments on the same segment can communicate with each other. The default value is false. When set to true, the only routes available will either be shared routes through the share actions, which are attachments in other segments, or static routes. For example, you might have a segment dedicated to development that should never allow VPCs to talk to each other, even if they’re on the same segment. In this example, you would set the parameter to true.


      Routes coming from a route table attachment are not affected by the isolate-attachments parameter. You are responsible for managing routes propagating from their attached route tables. Routes flowing into the route table attachment from other attachments within the segment follow the standard isolate-attachments behavior

    • require-attachment-acceptance — (Optional) This Boolean setting determines whether attachment requests are automatically approved or require acceptance. The default is true, indicating that attachment requests require acceptance. For example, you might use this setting to allow a sandbox segment to allow any attachment request so that a core network or attachment administrator does not need to review and approve attachment requests. In this example, require-attachment-acceptance is set to true.


      If require-attachment-acceptance is false for a segment, it's still possible for attachments to be added to or removed from a segment automatically when their tags change. If this behavior is not desired, set require-attachment-acceptance to true.

    • deny-filter — (Optional) An array of segments that disallows routes from the segments listed in the array. It is applied only after routes have been shared in segment-actions. If a segment is listed in the deny-filter, attachments between the two segments will never have routes shared across them. For example, you might have a financial payment segment that should never share routes with a development segment, regardless of how many other share statements are created. Adding the payments segment to the deny-filter parameter prevents any shared routes from being created with other segments.

    • allow-filter (optional) — An array of segments that explicitly allows only routes from the segments that are listed in the array. Use the allow-filter setting if a segment has a well-defined group of other segments that connectivity should be restricted to. It is applied after routes have been shared in segment-actions. If a segment is listed in allow-filter, attachments between the two segments will have routes if they are also shared in the segment-actions area. For example, you might have a segment named video-producer that should only ever share routes with a video-distributor segment, no matter how many other share statements are created.


      You can use either allow-filter or deny-filter, but you can't use both of them simultaneously. These are optional fields used to more explicitly control segment sharing. These parameters are not required in order to receive or send routes between segments.


segment-actions define how routing works between segments. By default, attachments can only communicate with other attachments in the same segment. You can use segment-actions to:

  • share attachments across segments. Use the share action so that attachments from two different segments can reach each other. For example, if you’ve set a segment to isolate-attachments, the segment can't reach anything unless it has a share relationship with other segments. The share statement creates routes between attachments in the provided segments. If you're creating a share between one segment and an array of segments, the segment to share allows attachments from the segments in the array. However, sharing does not occur between the segments within the array. For example, if a segment named shared-service is defined as a segment with a share-with array of segments named prod and prod2, the network policy will allow the attachments in both prod and prod2 to reach shared-service. But the network policy will not allow sharing of attachments between prod and prod2.

  • create-route to define a static route in a segment.


Sharing routes occurs between segments. All attachments connected to the same segment will share a similar routing behavior globally. If some attachments differ from other attachments in the same segment, those attachments should be within their own segments. This is intentional to prevent a proliferation of segments where one segment equals one attachment.

segment-actions is an optional section.


The following parameters are used in segment-actions:

  • action — The action to take for the chosen segment. The action must be either share or create-route. The following parameters are described for these actions.

  • share parameters. If the action to take is share, the following parameters are required. share is the default action behavior.

    • segment — The name of the segment created in the segments section to share.

    • modeattachment-route is the only supported value. This mode places the attachment and return routes in each of the share-with segments. For example, if there are static routes or routes shared from other segments, those will not be shared through the attachment-route mode.

    • share-with — An array of segments that will have reachability with the segment defined. The core network will create mutual advertisements between these share-with segments and the defined segment attachments.

      For example, if you create a share between a segment named shared-services and share-with “A” and “B”, this allows the attachments from “A” and “B” to reach “Shared services”. “A” and “B” cannot reach each other, and any static routes or routes propagated from other segments are not shared among these segments.

      Use "*" as a wild card to reference all segments instead of explicitly calling out segments individually.

    • except — Explicitly exclude segments, encapsulated within a share-with block. For example,

      { "action": "share", "mode": "attachment-route", "segment": "segment", "share-with": { "except": [ "dev", "prod" ] } }
  • create-route parameters. If the action is create-route, the following are the required and optional parameters.

    • segment — The name of the segment created in the segments section, which must be a static route. If you need to duplicate the static route in multiple segments, use multiple create-route statements.

    • destination-cidr-blocks — The static route to create. A segment should have the same routing behavior for a certain destination. This means if one Region has a route to a destination, other Regions should also have that route, but with potentially different paths. You can define the IPv4 and IPv6 CIDR notation for each AWS Region. For example, or 2001:db8::/56. This is an array of CIDR notation strings.

    • destinations — Defines the list of attachments to send the traffic to, with up to one attachment-id per Region. Because a segment is a global object, you should design your routing so that every AWS Region has an attachment in the destinations list. Regions that do not have attachments in this list will receive a propagated version of this route through cross-Region peering connections, and will use the static route of another Region. If multiple attachments are defined for a single Region, a single attachment will be chosen at random (deterministically random). This is the same case for multiple attachments that are defined across multiple remote Regions. Instead of an array of attachments, you can also provide a blackhole, which drops all traffic to the destination-cidr-blocks.

      • AWS Cloud WAN does not propagate blackhole routes.

    • description — (Optional) A user-defined description to help further identify this route.


In a core network, all attachments use the attachment-policies section to map an attachment to a segment. Instead of manually associating a segment to each attachment, attachments use tags. The tags are then used to associate the attachment to the specified segment. A core network supports the following types of attachments:

  • Transit Gateway Connect — connect

  • VPC — vpc

  • VPN — site-to-site-vpn

  • Transit Gateway route table — transit-gateway-route-table

For example, to attach a VPC to a core network, either the VPC owner or the core network owner would create a core network attachment in the core network using either the AWS Cloud WAN console or the Network Manager create-attachment command line or API. The attachment itself will have tags analyzed by the attachment policy, and not the tags associated with the VPC resource. A tag on the attachment such as “environment” : “development” would then map to a development segment. Attachment policy rules can also use available metadata from within the conditions, such as account ID, type of attachment, the resource ID (for example, vpc-id), or the AWS Region.

Rules are assigned numbers for processing, and are processed in order by number, from lowest to highest. When a match is made, the action is taken and no further rules are processed. A single attachment can only be associated to a single segment. If no rules are matched (for example, there might be a misspelled tag value), the attachment won't be associated to a segment.

When an attachment matches a rule, the attachment attaches to the segment defined segment. Each attachment can either be associated without acceptance or require a separate action to approve the attachment association. By default, every segment requires all attachments to be accepted. The acceptance requirement can be turned off with “require-attachment-acceptance” : false in the segment definition. When require-acceptance is false, any attachment that maps to the segment is automatically added. For example, a developer sandbox segment might want to allow any attachment with the correct tag to be added to the network. With the attachment-policies, you can add additional controls on a per-rule basis. For example, if attachments from the us-east-2 Region require acceptance but other Regions do not, you can set the “require-acceptance” : true setting on a rule that is specific to us-east-2 .

You can apply multiple conditions using either and or or logic to create a single rule. For example, you can state that if the account is 111122223333 and includes the tag “stage” : “development” it should map to a specified segment. If you don't want to use tags to map attachments, you could use the resource-id to manually map each incoming connection to a segment. However, this approach requires changing the policy document every time new attachments are added and can reduce the operability of your current LIVE policy.

attachment-policies is an optional section.


The following parameters are used in attachment-policies:

  • rule-number — An integer from 1 to 65535 indicating the rule's order number. Rules are processed in order from the lowest numbered rule to the highest. Rules stop processing when a rule is matched. It's important to make sure that you number your rules in the exact order that you want them processed.

  • description — (Optional) A user-defined description that further helps identify the rule.

  • condition-logic — Evaluates a condition on either and or or. This is a mandatory parameter only if you have more than one condition. The conditions themselves are unordered, so the condition-logic applies to all of the conditions for a rule, which also means nested conditions of and or or are not supported. Use and if you want to the rule to match on all of the conditions, or use or if you want the rule to match on one of the conditions.

  • conditions — An array composed of one of the four following types:

    1. type where the value is any — This matches any request. For example, you could use any if you're only using one segment that everything should map to. Or, you could use this as a fallback segment if you want all attachments that don't match a rule to map to a known segment.

    2. type where

      • value = resource-id | account-id | region | attachment-type

      • operator = equals | not-equals | contains | begins-with

      This type is the value compared against the operator. For example, you might use the condition type in the following way:

      • where the resource-id uses the resource associated with the attachment (for example, vpc-1234567890123456)

      • where the account-id uses the account ID of the requesting attachment (for example, 111122223333)

      • where the Region uses the Region code for the requesting attachment (for example, us-east-1), and

      • where the attachment-type uses vpc, site-to-site-vpn, connect, or transit-gateway-route-table strings

    3. type where the value is tag-exists — A string that matches against any of the keys defined on the attachment. Use this type when the value of the tag is not important, or if there is only a key without a value.

    4. type where the value is tag-value — Evaluates the following key value parameters:

      • key — A string that matches against any of the keys defined on the attachment. It must be an exact match of the key.

      • operator — The operation to perform against the key value. Must be one of equals | not-equals | contains | begins-with.

      • value — The value of the key to be evaluated for the operator.

      In this example,

      “type” : “tag-value”,

      “key” : “project”,

      “operator” : “begins-with”,

      “value” : “sta”

      Any condition where the value of project begins with sta is matched against the condition. This would return staging, stage, etc.

  • description — A user-defined description to help further identify the attachment policy.

  • action — The action to take when a condition is true.

    • association-method — Defines how a segment is mapped. Values can be constant or tag. constant statically defines the segment to associate the attachment to. tag uses the value of a tag to dynamically try to map to a segment.

    • segment — The name of the segment to share as defined in the segments section. This is used only when the association-method is constant.

    • tag-value-of-key — Maps the attachment to the value of a known key. This is used with the association-method is tag. For example a tag of “stage” : “test”, will map to a segment named test. The value must exactly match the name of a segment. This allows you to have many segments, but use only a single rule without having to define multiple nearly identical conditions. This prevents creating many similar conditions that all use the same keys to map to segments.

    • require-acceptance — Determines if this mapping should override the segment value for require-attachment-acceptance. You can only set this to true, indicating that this setting applies only to segments that have require-attachment-acceptance set to false. If the segment already has the default require-attachment-acceptance, you can set this to inherit segment’s acceptance value.