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CISC-RT-000500 - The Cisco BGP switch must be configured to reject inbound route advertisements for any prefixes belonging to the local autonomous system (AS) - AS

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Information

Accepting route advertisements belonging to the local AS can result in traffic looping or being black-holed, or at a minimum, using a non-optimized path.

Solution

Configure the switch to reject inbound route advertisements for any prefixes belonging to the local AS.

Step 1: Add to the prefix filter list those prefixes belonging to the local autonomous system.

SW1(config)# ip prefix-list PREFIX_FILTER seq 74 deny x.13.1.0/24 le 32

Step 2: If not already completed to be compliant with previous requirement, apply the prefix list filter inbound to each external BGP 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 PREFIX_FILTER in
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 PREFIX_FILTER in
SW1(config-router-neighbor-af)# end

See Also

https://dl.dod.cyber.mil/wp-content/uploads/stigs/zip/U_Cisco_NX-OS_Switch_Y24M04_STIG.zip

Item Details

References: CAT|II, CCI|CCI-001368, Rule-ID|SV-221104r622190_rule, STIG-ID|CISC-RT-000500, STIG-Legacy|SV-111027, STIG-Legacy|V-101923, Vuln-ID|V-221104

Plugin: Cisco

Control ID: 8be7fda76912e89cfc5850f4380185ccb3c4db60b6d299027ee70431c648eacc