The Cisco BGP switch 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-221107r622190_rule
Severity: Medium
References: CCI-001097
Updated: 8 months ago

Step 1: Configure a prefix list for containing all customer and local AS prefixes as shown in the example below:

SW1(config)# ip prefix-list FILTER_CORE_PREFIXES deny x.1.1.0/24 le 32
SW1(config)# ip prefix-list FILTER _CORE_PREFIXES deny x.1.2.0/24 le 32
SW1(config)# ip prefix-list FILTER _CORE_PREFIXES permit 0.0.0.0/0 ge 8
Step 2: Apply the prefix list filter outbound to each CE neighbor as shown in the example below:

SW1(config)# router bgp xx
SW1(config-router)# neighbor x.1.12.2
SW1(config-router-neighbor)# address-family ipv4 unicast
SW1(config-router-neighbor-af)# prefix-list FILTER _CORE_PREFIXES out
SW1(config-router-neighbor-af)# exit
SW1(config-router-neighbor)# exit
SW1(config-router)# neighbor x.2.44.4
SW1(config-router-neighbor)# address-family ipv4 unicast
SW1(config-router-neighbor-af)# prefix-list FILTER _CORE_PREFIXES out 
SW1(config-router-neighbor-af)# end

The Cisco BGP switch must be configured to reject outbound route advertisements for any prefixes belonging to the IP core.

Description

Remediation - Manual Procedure