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The Cisco BGP router must be configured to reject inbound route advertisements for any Bogon prefixes.
Overview
| Finding ID | Version | Rule ID | IA Controls | Severity |
|---|---|---|---|---|
| V-96947 | CISC-RT-000490 | SV-106085r1_rule | Medium |
| Description |
|---|
| Accepting route advertisements for Bogon prefixes can result in the local autonomous system (AS) becoming a transit for malicious traffic as it will in turn advertise these prefixes to neighbor autonomous systems. |
| STIG | Date |
|---|---|
| Cisco IOS XE Router RTR Security Technical Implementation Guide | 2019-07-25 |
Details
| Check Text ( C-95783r3_chk ) |
|---|
| Review the router configuration to verify that it will reject BGP routes for any Bogon prefixes. Step 1: Verify a prefix list has been configured containing the current Bogon prefixes as shown in the example below: ip prefix-list PREFIX_FILTER seq 5 deny 0.0.0.0/8 le 32 ip prefix-list PREFIX_FILTER seq 10 deny 10.0.0.0/8 le 32 ip prefix-list PREFIX_FILTER seq 15 deny 100.64.0.0/10 le 32 ip prefix-list PREFIX_FILTER seq 20 deny 127.0.0.0/8 le 32 ip prefix-list PREFIX_FILTER seq 25 deny 169.254.0.0/16 le 32 ip prefix-list PREFIX_FILTER seq 30 deny 172.16.0.0/12 le 32 ip prefix-list PREFIX_FILTER seq 35 deny 192.0.2.0/24 le 32 ip prefix-list PREFIX_FILTER seq 40 deny 192.88.99.0/24 le 32 ip prefix-list PREFIX_FILTER seq 45 deny 192.168.0.0/16 le 32 ip prefix-list PREFIX_FILTER seq 50 deny 198.18.0.0/15 le 32 ip prefix-list PREFIX_FILTER seq 55 deny 198.51.100.0/24 le 32 ip prefix-list PREFIX_FILTER seq 60 deny 203.0.113.0/24 le 32 ip prefix-list PREFIX_FILTER seq 65 deny 224.0.0.0/4 le 32 ip prefix-list PREFIX_FILTER seq 70 deny 240.0.0.0/4 le 32 ip prefix-list PREFIX_FILTER seq 75 permit 0.0.0.0/0 ge 8 Step 2: Verify that the prefix list has been applied to all external BGP peers as shown in the example below: router bgp xx no synchronization bgp log-neighbor-changes neighbor x.1.1.9 remote-as yy neighbor x.1.1.9 prefix-list PREFIX_FILTER in neighbor x.2.1.7 remote-as zz neighbor x.2.1.7 prefix-list PREFIX_FILTER in Route Map Alternative: Verify that the route map applied to the external neighbors references the configured Bogon prefix list shown above. router bgp xx no synchronization bgp log-neighbor-changes neighbor x.1.1.9 remote-as yy neighbor x.1.1.9 route-map FILTER_PREFIX_MAP neighbor x.2.1.7 remote-as zz neighbor x.2.1.7 route-map FILTER_PREFIX_MAP … route-map FILTER_PREFIX_MAP permit 10 match ip address prefix-list BOGON_PREFIXES If the router is not configured to reject inbound route advertisements for any Bogon prefixes, this is a finding. |
| Fix Text (F-102627r1_fix) |
|---|
| Configure the router to reject inbound route advertisements for any Bogon prefixes. Step 1: Configure a prefix list containing the current Bogon prefixes as shown below: R1(config)#ip prefix-list PREFIX_FILTER deny 0.0.0.0/8 le 32 R1(config)#ip prefix-list PREFIX_FILTER deny 10.0.0.0/8 le 32 R1(config)#ip prefix-list PREFIX_FILTER deny 100.64.0.0/10 le 32 R1(config)#ip prefix-list PREFIX_FILTER deny 127.0.0.0/8 le 32 R1(config)#ip prefix-list PREFIX_FILTER deny 169.254.0.0/16 le 32 R1(config)#ip prefix-list PREFIX_FILTER deny 172.16.0.0/12 le 32 R1(config)#ip prefix-list PREFIX_FILTER deny 192.0.2.0/24 le 32 R1(config)#ip prefix-list PREFIX_FILTER deny 192.88.99.0/24 le 32 R1(config)#ip prefix-list PREFIX_FILTER deny 192.168.0.0/16 le 32 R1(config)#ip prefix-list PREFIX_FILTER deny 198.18.0.0/15 le 32 R1(config)#ip prefix-list PREFIX_FILTER deny 198.51.100.0/24 le 32 R1(config)#ip prefix-list PREFIX_FILTER deny 203.0.113.0/24 le 32 R1(config)#ip prefix-list PREFIX_FILTER deny 224.0.0.0/4 le 32 R1(config)#ip prefix-list PREFIX_FILTER deny 240.0.0.0/4 le 32 R1(config)#ip prefix-list PREFIX_FILTER deny 240.0.0.0/4 le 32 R1(config)#ip prefix-list PREFIX_FILTER permit 0.0.0.0/0 ge 8 Step 2: Apply the prefix list filter inbound to each external BGP neighbor as shown in the example: R1(config)#router bgp xx R1(config-router)#neighbor x.1.1.9 prefix-list PREFIX_FILTER in R1(config-router)#neighbor x.2.1.7 prefix-list PREFIX_FILTER in Route Map Alternative: Step 1: Configure the route map referencing the configured prefix list above. R1(config)#route-map FILTER_PREFIX_MAP 10 R1(config-route-map)#match ip address prefix-list PREFIX_FILTER R1(config-route-map)#exit Step 2: Apply the route-map inbound to each external BGP neighbor as shown in the example: R1(config)#router bgp xx R1(config-router)#neighbor x.1.1.9 route-map FILTER_PREFIX_MAP in R1(config-router)#neighbor x.2.1.7 route-map FILTER_PREFIX_MAP in R1(config-router)#end |