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AWS Client VPN with OKTA

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Authorization rules with OKTA groups basic setup following this exact setup : https://aws.amazon.com/blogs/networking-and-content-delivery/authenticate-aws-client-vpn-users-with-saml/

Authorization rules are not restricting access when CIDR rule is not added , sometimes it allows access for everything regardless of there is a rule for it or not ( seems it uses the configured routes anyways) we are using TGW cross accounts to connect to other VPCs

Appreciate confirming how to restrict specific CIDRs only to specific OKTA groups (SAML ) ? is there anything I'm doing wrong here?

1 Answer
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Hello,

What you are seeing is expected behavior.

Refer the below 2 sections from the link shared.

Note

Client VPN uses longest prefix matching when evaluating authorization rules. See the troubleshooting topic Authorization rules for Active Directory groups not working as expected and Route priority in the Amazon VPC User Guide for more details.

Problem

I have configured authorization rules for my Active Directory groups, but they are not working as I expected. I have added an authorization rule for 0.0.0.0/0 to authorize traffic for all networks, but traffic still fails for specific destination CIDRs.

Cause

Authorization rules are indexed on network CIDRs. Authorization rules must grant Active Directory groups access to specific network CIDRs. Authorization rules for 0.0.0.0/0 are handled as a special case, and are therefore evaluated last, regardless of the order in which the authorization rules are created.

For example, say that you create five authorization rules in the following order:

Rule 1: Group 1 access to 10.1.0.0/16 Rule 2: Group 1 access to 0.0.0.0/0 Rule 3: Group 2 access to 0.0.0.0/0 Rule 4: Group 3 access to 0.0.0.0/0 Rule 5: Group 2 access to 172.131.0.0/16

In this example, Rule 2, Rule 3, and Rule 4 are evaluated last. Group 1 has access to 10.1.0.0/16 only, and Group 2 has access to 172.131.0.0/16 only. Group 3 does not have access to 10.1.0.0/16 or 172.131.0.0/16, but it has access to all other networks. If you remove Rules 1 and 5, all three groups have access to all networks.

Solution:

Verify that you create authorization rules that explicitly grant Active Directory groups access to specific network CIDRs. For example If you add an authorization rule for 0.0.0.0/0, keep in mind that it will be evaluated last, and that previous authorization rules may limit the networks to which it grants access.

Hope this helps !!

Reference: https://docs.aws.amazon.com/vpn/latest/clientvpn-admin/cvpn-working-rules.html

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answered 2 months ago

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