The Cisco BGP router must be configured to reject outbound route advertisements for any prefixes belonging to the IP core.
Overview
| Finding ID | Version | Rule ID | IA Controls | Severity |
| V-216781 | CISC-RT-000530 | SV-216781r531087_rule | CCI-001097 | medium |
| Description | ||||
| 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. | ||||
| STIG | Date | |||
| Cisco IOS XR Router RTR Security Technical Implementation Guide | 2024-08-22 | |||
Details
Check Text (C-216781r531087_chk)
Step 1: verify that an outbound route policy has been configured for each external neighbor as shown in the example below.
router bgp xx
address-family ipv4 unicast
!
neighbor x.1.23.3
remote-as yy
address-family ipv4 unicast
route-policy BGP_FILTER_OUTBOUND out
!
!
neighbor x.1.24.4
remote-as zz
address-family ipv4 unicast
route-policy BGP_FILTER_OUTBOUND out
!
!
Step 2: Review the route policy to determine if it is filtering at a minimum IP core prefixes as shown in the example below.
route-policy BGP_FILTER_OUTBOUND
if destination in CORE_PREFIX then
drop
else
pass
endif
end-policy
Step 3: Review the prefix set referenced in the route policy above to determine if it includes the IP core prefix as shown in the example below.
prefix-set CORE_PREFIX
10.1.1.0/24 le 32
end-set
If the router is not configured to reject outbound route advertisements for prefixes belonging to the IP core, this is a finding.
Fix Text (F-18011r288721_fix)
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