Information
Packets with Bogon IP source addresses should never be allowed to traverse the IP core. Bogon IP networks are RFC1918 addresses or address blocks that have never been assigned by the IANA or have been reserved.
NOTE: Nessus has provided the target output to assist in reviewing the benchmark to ensure target compliance.
Solution
Configure the perimeter to block inbound packets with Bogon source addresses.
Step 1: Configure an ACL containing the current Bogon prefixes as shown below:
SW1(config)#ip access-list extended FILTER_PERIMETER
SW1(config-ext-nacl)#deny ip 0.0.0.0 0.255.255.255 any log-input
SW1(config-ext-nacl)#deny ip 10.0.0.0 0.255.255.255 any log-input
SW1(config-ext-nacl)#deny ip 100.64.0.0 0.63.255.255 any log-input
SW1(config-ext-nacl)#deny ip 127.0.0.0 0.255.255.255 any log-input
SW1(config-ext-nacl)#deny ip 169.254.0.0 0.0.255.255 any log-input
SW1(config-ext-nacl)#deny ip 172.16.0.0 0.15.255.255 any log-input
SW1(config-ext-nacl)#deny ip 192.0.0.0 0.0.0.255 any log-input
SW1(config-ext-nacl)#deny ip 192.0.2.0 0.0.0.255 any log-input
SW1(config-ext-nacl)#deny ip 192.168.0.0 0.0.255.255 any log-input
SW1(config-ext-nacl)#deny ip 198.18.0.0 0.1.255.255 any log-input
SW1(config-ext-nacl)#deny ip 198.51.100.0 0.0.0.255 any log-input
SW1(config-ext-nacl)#deny ip 203.0.113.0 0.0.0.255 any log-input
SW1(config-ext-nacl)#deny ip 224.0.0.0 31.255.255.255 any log-input
SW1(config-ext-nacl)#deny ip 240.0.0.0 31.255.255.255 any log-input
SW1(config-ext-nacl)#permit tcp any any established
SW1(config-ext-nacl)#permit icmp host x.12.1.9 host x.12.1.10 echo
SW1(config-ext-nacl)#permit icmp host x.12.1.9 host x.12.1.10 echo-reply
...
...
...
SW1(config-ext-nacl)#deny ip any any log-input
SW1(config-ext-nacl)#end
Step 2: Apply the ACL inbound on all external interfaces.
SW1(config)#int g0/0
SW1(config-if)#ip access-group FILTER_PERIMETER in
SW1(config-if)#end