The Cisco BGP switch must be configured to reject inbound route advertisements for any Bogon prefixes.

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.

Review the switch 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 router-id 10.1.1.1 neighbor x.1.12.2 remote-as xx password 3 7b07d1b3023056a9 address-family ipv4 unicast prefix-list PREFIX_FILTER in neighbor x.2.44.4 remote-as xx password 3 f07a10cb41db8bb6f8f0a340049a9b02 address-family ipv4 unicast 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. route-map FILTER_PREFIX_MAP permit 10 match ip address prefix-list PREFIX_FILTER … … … router bgp xx router-id 10.1.1.1 neighbor x.1.12.2 remote-as xx password 3 7b07d1b3023056a9 address-family ipv4 unicast route-map FILTER_PREFIX_MAP in neighbor x.2.44.4 remote-as xx password 3 f07a10cb41db8bb6f8f0a340049a9b02 address-family ipv4 unicast route-map FILTER_PREFIX_MAP in If the switch is not configured to reject inbound route advertisements for any Bogon prefixes, this is a finding.

Configure the switch to reject inbound route advertisements for any Bogon prefixes. Step 1: Configure a prefix list containing the current Bogon prefixes as shown below: SW1(config)# ip prefix-list PREFIX_FILTER seq 5 deny 0.0.0.0/8 le 32 SW1(config)# ip prefix-list PREFIX_FILTER seq 10 deny 10.0.0.0/8 le 32 SW1(config)# ip prefix-list PREFIX_FILTER seq 15 deny 100.64.0.0/10 le 32 SW1(config)# ip prefix-list PREFIX_FILTER seq 20 deny 127.0.0.0/8 le 32 SW1(config)# ip prefix-list PREFIX_FILTER seq 25 deny 169.254.0.0/16 le 32 SW1(config)# ip prefix-list PREFIX_FILTER seq 30 deny 172.16.0.0/12 le 32 SW1(config)# ip prefix-list PREFIX_FILTER seq 35 deny 192.0.2.0/24 le 32 SW1(config)# ip prefix-list PREFIX_FILTER seq 40 deny 192.88.99.0/24 le 32 SW1(config)# ip prefix-list PREFIX_FILTER seq 45 deny 192.168.0.0/16 le 32 SW1(config)# ip prefix-list PREFIX_FILTER seq 50 deny 198.18.0.0/15 le 32 SW1(config)# ip prefix-list PREFIX_FILTER seq 55 deny 198.51.100.0/24 le 32 SW1(config)# ip prefix-list PREFIX_FILTER seq 60 deny 203.0.113.0/24 le 32 SW1(config)# ip prefix-list PREFIX_FILTER seq 65 deny 224.0.0.0/4 le 32 SW1(config)# ip prefix-list PREFIX_FILTER seq 70 deny 240.0.0.0/4 le 32 SW1(config)# ip prefix-list PREFIX_FILTER seq 75 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 below: SW1(config)# router bgp xx SW1(config-router)# neighbor x.1.12.2 SW1(config-router-neighbor)# address-family ipv4 unicast SW1(config-router-neighbor-af)# prefix-list PREFIX_FILTER in SW1(config-router-neighbor-af)# exit SW1(config-router-neighbor)# exit SW1(config-router)# neighbor x.2.44.4 SW1(config-router-neighbor)# address-family ipv4 unicast SW1(config-router-neighbor-af)# prefix-list PREFIX_FILTER in SW1(config-router-neighbor-af)# end Route Map Alternative Step 1: Configure the route map referencing the configured prefix list above. SW1(config)# route-map FILTER_PREFIX_MAP permit 10 SW1(config-route-map)# match ip address prefix-list PREFIX_FILTER SW1(config-route-map)# exit Step 2: Apply the route-map inbound to each external BGP neighbor as shown in the example below: SW1(config)# router bgp xx SW1(config-router)# neighbor x.1.12.2 SW1(config-router-neighbor)# address-family ipv4 unicast SW1(config-router-neighbor-af)# route-map FILTER_PREFIX_MAP in SW1(config-router-neighbor-af)# exit SW1(config-router-neighbor)# exit SW1(config-router)# neighbor x.2.44.4 SW1(config-router-neighbor)# address-family ipv4 unicast SW1(config-router-neighbor-af)# route-map FILTER_PREFIX_MAP in SW1(config-router-neighbor-af)# end