The Cisco BGP router must be configured to reject outbound route advertisements for any prefixes belonging to the IP core.
An XCCDF Rule
Description
<VulnDiscussion>Outbound route advertisements belonging to the core can result in traffic either looping or being black holed, or at a minimum, using a non-optimized path.</VulnDiscussion><FalsePositives></FalsePositives><FalseNegatives></FalseNegatives><Documentable>false</Documentable><Mitigations></Mitigations><SeverityOverrideGuidance></SeverityOverrideGuidance><PotentialImpacts></PotentialImpacts><ThirdPartyTools></ThirdPartyTools><MitigationControl></MitigationControl><Responsibility></Responsibility><IAControls></IAControls>
- ID
- SV-216691r929058_rule
- Severity
- Medium
- References
- Updated
Remediation - Manual Procedure
Step 1: Configure a prefix list for containing all customer and local AS prefixes as shown in the example below:
R1(config)#ip prefix-list FILTER_CORE_PREFIXES deny x.1.1.0/24 le 32
R1(config)#ip prefix-list FILTER _CORE_PREFIXES deny x.1.2.0/24 le 32
R1(config)#ip prefix-list FILTER _CORE_PREFIXES permit 0.0.0.0/0 ge 8