CISC-RT-000530 - The Cisco BGP switch must be configured to reject outbound route advertisements for any prefixes belonging to the IP core.

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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:

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

See Also

https://dl.dod.cyber.mil/wp-content/uploads/stigs/zip/U_Cisco_NX-OS_Switch_Y24M07_STIG.zip

Item Details

References: CAT|II, CCI|CCI-001097, Rule-ID|SV-221107r999716_rule, STIG-ID|CISC-RT-000530, STIG-Legacy|SV-111033, STIG-Legacy|V-101929, Vuln-ID|V-221107

Plugin: Cisco

Control ID: 7ea28bb6dc0f6bc421c517cebf598cae47eb72cc37d53c00b854ea27efe4f0cd