Ensure all eBGP routers are configured to reject inbound route advertisements for any Bogon prefixes.
Step 1: Configure a prefix list containing the current Bogon prefixes.
OS10(config)# ip prefix-list BOGON_PREFIX_FILTER seq 5 deny 0.0.0.0/8 le 32
OS10(config)# ip prefix-list BOGON_PREFIX_FILTER seq 10 deny 10.0.0.0/8 le 32OS10(config)# ip prefix-list BOGON_PREFIX_FILTER seq 15 deny 100.64.0.0/10 le 32
OS10(config)# ip prefix-list BOGON_PREFIX_FILTER seq 20 deny 127.0.0.0/8 le 32
OS10(config)# ip prefix-list BOGON_PREFIX_FILTER seq 25 deny 169.254.0.0/16 le 32
OS10(config)# ip prefix-list BOGON_PREFIX_FILTER seq 30 deny 172.16.0.0/12 le 32
OS10(config)# ip prefix-list BOGON_PREFIX_FILTER seq 35 deny 192.0.2.0/24 le 32
OS10(config)# ip prefix-list BOGON_PREFIX_FILTER seq 40 deny 192.88.99.0/24 le 32
OS10(config)# ip prefix-list BOGON_PREFIX_FILTER seq 45 deny 192.168.0.0/16 le 32
OS10(config)# ip prefix-list BOGON_PREFIX_FILTER seq 50 deny 198.18.0.0/15 le 32
OS10(config)# ip prefix-list BOGON_PREFIX_FILTER seq 55 deny 198.51.100.0/24 le 32
OS10(config)# ip prefix-list BOGON_PREFIX_FILTER seq 60 deny 203.0.113.0/24 le 32
OS10(config)# ip prefix-list BOGON_PREFIX_FILTER seq 65 deny 224.0.0.0/4 le 32
OS10(config)# ip prefix-list BOGON_PREFIX_FILTER seq 70 deny 240.0.0.0/4 le 32
OS10(config)# ip prefix-list BOGON_PREFIX_FILTER seq 75 permit 0.0.0.0/0 ge 8
Step 2: Configure the route map referencing the configured Bogon prefix list.
OS10(config)# route-map PREFIX_FILTER_MAP 10
OS10(config-route-map)# match ip address prefix-list BOGON_PREFIX_FILTER
OS10(config-route-map)# exit
Step 3: Apply the route-map inbound to each external BGP neighbor.
OS10(config)# router bgp 10
OS10(config-router-bgp-10)# neighbor 123.1.1.10
OS10(config-router-neighbor)# address-family ipv4 unicast
OS10(config-router-bgp-neighbor-af)# route-map PREFIX_FILTER_MAP in
OS10(config-router-bgp-neighbor-af)# exit
OS10(config-router-neighbor)# exit
OS10(config-router-bgp-10)# template ebgp
OS10(config-router-template)# address-family ipv4 unicast
OS10(config-router-bgp-template-af)# route-map PREFIX_FILTER_MAP in
OS10(config-router-bgp-template-af)# exit
OS10(config-router-template)# exit
OS10(config-router-bgp-10)# exit