The Cisco BGP switch must be configured to reject route advertisements from CE switches with an originating AS in the AS_PATH attribute that does not belong to that customer.
An XCCDF Rule
Description
<VulnDiscussion>Verifying the path a route has traversed will ensure that the local AS is not used as a transit network for unauthorized traffic. To ensure that the local AS does not carry any prefixes that do not belong to any customers, all PE switches must be configured to reject routes with an originating AS other than that belonging to the customer.</VulnDiscussion><FalsePositives></FalsePositives><FalseNegatives></FalseNegatives><Documentable>false</Documentable><Mitigations></Mitigations><SeverityOverrideGuidance></SeverityOverrideGuidance><PotentialImpacts></PotentialImpacts><ThirdPartyTools></ThirdPartyTools><MitigationControl></MitigationControl><Responsibility></Responsibility><IAControls></IAControls>
- ID
- SV-221109r999718_rule
- Severity
- Low
- References
- Updated
Remediation - Manual Procedure
Configure the switch to deny updates received from eBGP peers that do not list their AS number as the first AS in the AS_PATH attribute.
Step 1: Configure the as-path ACL as shown in the example below:
SW1(config)# ip as-path access-list AS_PATH permit ^22$
SW1(config)# ip as-path access-list AS_PATH deny .*