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 set containing the IP core prefix as shown below.

RP/0/0/CPU0:R2(config)#prefix-set

Step 2: Configure a prefix set containing the current Bogon prefixes as shown below.

RP/0/0/CPU0:R2(config)#prefix-set CORE_PREFIX
RP/0/0/CPU0:R2(config-pfx)#10.1.1.0/24 le 32
RP/0/0/CPU0:R2(config-pfx)#end-set

Step 3: Configure the route policy to drop route advertisements for IP core prefixes as shown in the example below.

RP/0/0/CPU0:R2(config)#route-policy BGP_FILTER_OUTBOUND
RP/0/0/CPU0:R2(config-rpl)#if destination in CORE_PREFIX then
RP/0/0/CPU0:R2(config-rpl-if)#drop
RP/0/0/CPU0:R2(config-rpl-if)#else
RP/0/0/CPU0:R2(config-rpl-else)#pass
RP/0/0/CPU0:R2(config-rpl-else)#endif
RP/0/0/CPU0:R2(config-rpl)#end-policy

Step 4: Apply the route policy to each external BGP neighbor as shown in the example.

RP/0/0/CPU0:R2(config)#router bgp xx
RP/0/0/CPU0:R2(config-bgp)#neighbor x.1.23.3
RP/0/0/CPU0:R2(config-bgp-nbr)#address-family ipv4 unicast
RP/0/0/CPU0:R2(config-bgp-nbr-af)#route-policy BGP_FILTER_OUTBOUND out
RP/0/0/CPU0:R2(config-bgp)#neighbor x.1.24.4
RP/0/0/CPU0:R2(config-bgp-nbr)#address-family ipv4 unicast
RP/0/0/CPU0:R2(config-bgp-nbr-af)#route-policy BGP_FILTER_ OUTBOUND out

See Also

https://dl.dod.cyber.mil/wp-content/uploads/stigs/zip/U_Cisco_IOS-XR_Router_Y24M07_STIG.zip

Item Details

Category: SYSTEM AND COMMUNICATIONS PROTECTION

References: 800-53|SC-7a., CAT|II, CCI|CCI-001097, Rule-ID|SV-216781r531087_rule, STIG-ID|CISC-RT-000530, STIG-Legacy|SV-105907, STIG-Legacy|V-96769, Vuln-ID|V-216781

Plugin: Cisco

Control ID: b7aa489c54b2696b7f8e3f46e3d5f6e2369ec65911329d2f007f01f892510415