The Cisco BGP router must be configured to reject outbound route advertisements for any prefixes that do not belong to any customers or the local autonomous system (AS).

Severity
Group ID
Group Title
Version
Rule ID
Date
STIG Version
mediumV-216780SRG-NET-000018-RTR-000005CISC-RT-000520SV-216780r531087_rule2024-08-223
Description
Advertisement of routes by an autonomous system for networks that do not belong to any of its customers pulls traffic away from the authorized network. This causes a denial of service (DoS) on the network that allocated the block of addresses and may cause a DoS on the network that is inadvertently advertising it as the originator. It is also possible that a misconfigured or compromised router within the GIG IP core could redistribute IGP routes into BGP, thereby leaking internal routes.
ℹ️ Check
This requirement is not applicable for the DODIN Backbone. Step 1: verify that an outbound 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 CE_ADVERTISEMENTS out ! ! neighbor x.12.4.16 remote-as 64516 address-family ipv4 unicast route-policy CE_ADVERTISEMENTS out ! ! Step 2: Review the route policy to determine if it is accepting only prefixes belonging to customers or the local autonomous system as shown in the example below. route-policy CE_ADVERTISEMENTS if destination in CE_PREFIX_ADVERTISEMENTS then pass else drop endif end-policy Step 3: Review the prefix sets referenced in the route policy above to determine if they include only prefixes belonging to customers or the local autonomous system as shown in the example below. prefix-set CE_PREFIX_ADVERTISEMENTS x.13.1.0/24 le 32, x.13.2.0/24 le 32, x.13.3.0/24 le 32, x.13.4.0/24 le 32 end-set If the router is not configured to reject outbound route advertisements that do not belong to any customers or the local AS, this is a finding.
✔️ Fix
This requirement is not applicable for the DODIN Backbone. Step 1: Configure a prefix set for customer and local autonomous system prefixes as shown in the example. RP/0/0/CPU0:R2(config)#prefix-set CE_PREFIX_ADVERTISEMENTS RP/0/0/CPU0:R2(config-pfx)#x.13.1.0/24 le 32, RP/0/0/CPU0:R2(config-pfx)#x.13.2.0/24 le 32, RP/0/0/CPU0:R2(config-pfx)#x.13.3.0/24 le 32, RP/0/0/CPU0:R2(config-pfx)#x.13.4.0/24 le 32 RP/0/0/CPU0:R2(config-pfx)#end-set Step 2: Configure a route policy filter for allow customer and local autonomous system prefixes as shown in the example. RP/0/0/CPU0:R2(config)#route-policy CE_ADVERTISEMENTS RP/0/0/CPU0:R2(config-rpl)#if destination in CE_PREFIX_ADVERTISEMENTS 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 route-policy CE_ADVERTISEMENTS out 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 CE_ADVERTISEMENTS out RP/0/0/CPU0:R2(config-bgp-nbr-af)#end