The Cisco BGP router must be configured to reject inbound route advertisements from a customer edge (CE) router for prefixes that are not allocated to that customer.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-216779	CISC-RT-000510	SV-216779r531087_rule		Medium

Description
As a best practice, a service provider should only accept customer prefixes that have been assigned to that customer and any peering autonomous systems. A multi-homed customer with BGP speaking routers connected to the Internet or other external networks could be breached and used to launch a prefix de-aggregation attack. Without ingress route filtering of customers, the effectiveness of such an attack could impact the entire IP core and its customers.

Description

As a best practice, a service provider should only accept customer prefixes that have been assigned to that customer and any peering autonomous systems. A multi-homed customer with BGP speaking routers connected to the Internet or other external networks could be breached and used to launch a prefix de-aggregation attack. Without ingress route filtering of customers, the effectiveness of such an attack could impact the entire IP core and its customers.

STIG	Date
Cisco IOS XR Router RTR Security Technical Implementation Guide	2023-06-01

Details

Check Text ( C-18011r288714_chk )
Review the router configuration to verify that there are ACLs defined to only accept routes for prefixes that belong to specific customers. Step 1: Verify that an inbound route policy has been configured for each customer neighbor as shown in the example below. router bgp xx address-family ipv4 unicast ! neighbor x.12.4.14 remote-as 64514 address-family ipv4 unicast route-policy CUST1_PREFIX_FILTER in ! ! neighbor x.12.4.16 remote-as 64516 address-family ipv4 unicast route-policy CUST2_PREFIX_FILTER in ! ! Step 2: Review the route policies to determine if it is accepting only prefixes belonging to each customer as shown in the example below. route-policy CUST1_PREFIX_FILTER if destination in CUST1_PREFIX then pass else drop endif end-policy ! route-policy CUST2_PREFIX_FILTER if destination in CUST2_PREFIX then pass else drop endif end-policy Step 3: Review the prefix sets referenced in the route policies above to determine if they include only prefixes belonging to each customer. prefix-set CUST1_PREFIX x.1.1.0/24 le 32 end-set ! prefix-set CUST2_PREFIX x.2.1.0/24 le 32 end-set Note: Routes to PE-CE links within a VPN are needed for troubleshooting end-to-end connectivity across the MPLS/IP backbone. Hence, these prefixes are an exception to this requirement. If the router is not configured to reject inbound route advertisements from each CE router for prefixes that are not allocated to that customer, this is a finding.

Check Text ( C-18011r288714_chk )

Review the router configuration to verify that there are ACLs defined to only accept routes for prefixes that belong to specific customers.

Step 1: Verify that an inbound route policy has been configured for each customer neighbor as shown in the example below.

router bgp xx
address-family ipv4 unicast
!
neighbor x.12.4.14
remote-as 64514
address-family ipv4 unicast
route-policy CUST1_PREFIX_FILTER in
!
!
neighbor x.12.4.16
remote-as 64516
address-family ipv4 unicast
route-policy CUST2_PREFIX_FILTER in
!
!

Step 2: Review the route policies to determine if it is accepting only prefixes belonging to each customer as shown in the example below.

route-policy CUST1_PREFIX_FILTER
if destination in CUST1_PREFIX then
pass
else
drop
endif
end-policy
!
route-policy CUST2_PREFIX_FILTER
if destination in CUST2_PREFIX then
pass
else
drop
endif
end-policy

Step 3: Review the prefix sets referenced in the route policies above to determine if they include only prefixes belonging to each customer.

prefix-set CUST1_PREFIX
x.1.1.0/24 le 32
end-set
!
prefix-set CUST2_PREFIX
x.2.1.0/24 le 32
end-set

Note: Routes to PE-CE links within a VPN are needed for troubleshooting end-to-end connectivity across the MPLS/IP backbone. Hence, these prefixes are an exception to this requirement.

If the router is not configured to reject inbound route advertisements from each CE router for prefixes that are not allocated to that customer, this is a finding.

Fix Text (F-18009r288715_fix)
Configure the router to reject inbound route advertisements from each CE router for prefixes that are not allocated to that customer. Step 1: Configure a prefix set for each customer containing prefixes belonging to each as shown in the example. RP/0/0/CPU0:R2(config)#prefix-set CUST1_PREFIX RP/0/0/CPU0:R2(config-pfx)#x.1.1.0/24 le 32 RP/0/0/CPU0:R2(config-pfx)#end-set RP/0/0/CPU0:R2(config)#prefix-set CUST2_PREFIX RP/0/0/CPU0:R2(config-pfx)#x.2.1.0/24 le 32 RP/0/0/CPU0:R2(config-pfx)#end-set Step 2: Configure a route policy filter for each customer as shown in the example. RP/0/0/CPU0:R2(config)#route-policy CUST1_PREFIX_FILTER RP/0/0/CPU0:R2(config-rpl)#if destination in CUST1_PREFIX then RP/0/0/CPU0:R2(config-rpl-if)#pass RP/0/0/CPU0:R2(config-rpl-if)#else RP/0/0/CPU0:R2(config-rpl-else)#drop RP/0/0/CPU0:R2(config-rpl-else)#endif RP/0/0/CPU0:R2(config-rpl)#end-policy RP/0/0/CPU0:R2(config)#route-policy CUST2_PREFIX_FILTER RP/0/0/CPU0:R2(config-rpl)#if destination in CUST2_PREFIX then RP/0/0/CPU0:R2(config-rpl-if)#pass RP/0/0/CPU0:R2(config-rpl-if)#else RP/0/0/CPU0:R2(config-rpl-else)#drop RP/0/0/CPU0:R2(config-rpl-else)#endif RP/0/0/CPU0:R2(config-rpl)#end-policy Step 3: Apply the route policy to each customer neighbor as shown in the example. RP/0/0/CPU0:R2(config)#router bgp xx RP/0/0/CPU0:R2(config-bgp)#neighbor x.12.4.14 RP/0/0/CPU0:R2(config-bgp-nbr)#address-family ipv4 unicast RP/0/0/CPU0:R2(config-bgp-nbr-af)#route-policy CUST1_PREFIX_FILTER in RP/0/0/CPU0:R2(config-bgp)#neighbor x.12.4.16 RP/0/0/CPU0:R2(config-bgp-nbr)#address-family ipv4 unicast RP/0/0/CPU0:R2(config-bgp-nbr-af)#route-policy CUST2_PREFIX_FILTER in

Fix Text (F-18009r288715_fix)

Configure the router to reject inbound route advertisements from each CE router for prefixes that are not allocated to that customer.

Step 1: Configure a prefix set for each customer containing prefixes belonging to each as shown in the example.

RP/0/0/CPU0:R2(config)#prefix-set CUST1_PREFIX
RP/0/0/CPU0:R2(config-pfx)#x.1.1.0/24 le 32
RP/0/0/CPU0:R2(config-pfx)#end-set
RP/0/0/CPU0:R2(config)#prefix-set CUST2_PREFIX
RP/0/0/CPU0:R2(config-pfx)#x.2.1.0/24 le 32
RP/0/0/CPU0:R2(config-pfx)#end-set

Step 2: Configure a route policy filter for each customer as shown in the example.

RP/0/0/CPU0:R2(config)#route-policy CUST1_PREFIX_FILTER
RP/0/0/CPU0:R2(config-rpl)#if destination in CUST1_PREFIX then
RP/0/0/CPU0:R2(config-rpl-if)#pass
RP/0/0/CPU0:R2(config-rpl-if)#else
RP/0/0/CPU0:R2(config-rpl-else)#drop
RP/0/0/CPU0:R2(config-rpl-else)#endif
RP/0/0/CPU0:R2(config-rpl)#end-policy
RP/0/0/CPU0:R2(config)#route-policy CUST2_PREFIX_FILTER
RP/0/0/CPU0:R2(config-rpl)#if destination in CUST2_PREFIX then
RP/0/0/CPU0:R2(config-rpl-if)#pass
RP/0/0/CPU0:R2(config-rpl-if)#else
RP/0/0/CPU0:R2(config-rpl-else)#drop
RP/0/0/CPU0:R2(config-rpl-else)#endif
RP/0/0/CPU0:R2(config-rpl)#end-policy

Step 3: Apply the route policy to each customer neighbor as shown in the example.

RP/0/0/CPU0:R2(config)#router bgp xx
RP/0/0/CPU0:R2(config-bgp)#neighbor x.12.4.14
RP/0/0/CPU0:R2(config-bgp-nbr)#address-family ipv4 unicast
RP/0/0/CPU0:R2(config-bgp-nbr-af)#route-policy CUST1_PREFIX_FILTER in
RP/0/0/CPU0:R2(config-bgp)#neighbor x.12.4.16
RP/0/0/CPU0:R2(config-bgp-nbr)#address-family ipv4 unicast
RP/0/0/CPU0:R2(config-bgp-nbr-af)#route-policy CUST2_PREFIX_FILTER in