CISC-RT-000530 - The Cisco BGP router must be configured to reject outbound route advertisements for any prefixes belonging to the IP core - neighbor prefix-list

Information

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.

Solution

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

Step 2: Apply the prefix list filter outbound to each CE neighbor as shown in the example.

R1(config)#router bgp xx
R1(config-router)#neighbor x.1.4.12 prefix-list FILTER _CORE_PREFIXES out

See Also

https://dl.dod.cyber.mil/wp-content/uploads/stigs/zip/U_Cisco_IOS_Router_Y24M07_STIG.zip

Item Details

Category: SYSTEM AND COMMUNICATIONS PROTECTION

References: 800-53|SC-7a., CAT|II, CCI|CCI-001097, Rule-ID|SV-216601r531085_rule, STIG-ID|CISC-RT-000530, STIG-Legacy|SV-105741, STIG-Legacy|V-96603, Vuln-ID|V-216601

Plugin: Cisco

Control ID: efbd20a720193081ff754b4c6a8f634384779993f491797b8bd8c229f296dd5d