National Institute of Standards and Technology (NIST)'s Guidelines on Firewalls and Firewall Policy. The following traffic types should always be blocked:
- Inbound traffic from a non-authenticated source system with a destination address of the firewall itself
- Inbound traffic with a source address indicating that the packet originated on a network behind the firewall
- Inbound traffic containing ICMP
- Inbound or outbound traffic from a system using a source address that falls within the private address ranges show n in RFC 1918
- Inbound traffic from a non-authenticated source system containing SNMP
- Inbound traffic containing IP Source Routing information
- Inbound or outbound traffic containing a source or destination address of 127.0.0.1
- Inbound or outbound traffic containing a source or destination address of 0.0.0.0
- Inbound or outbound traffic containing a directed broadcast address
The whole article can be found at this link:
http://csrc.nist.gov/publications/nistpubs/800-41/sp800-41.pdfA good "base" ACL for use on Internet facing routers and firewall devices.
Assuming my PubNet range is a block of 32 66.238.29.0 - 31. See below
! no fragmentsaccess-list 100 deny tcp any 66.238.29.0 0.0.0.31 log fragments
access-list 100 deny udp any 66.238.29.0 0.0.0.31 log fragments
access-list 100 deny icmp any 66.238.29.0 0.0.0.31 log fragments
! no snmp inbound from the Internetaccess-list 100 deny udp any any eq snmp
access-list 100 deny udp any any eq snmptrap
! RFC 2827 Ingress, RFC 3804 Martian Filtering and RFC 1918 private Address Filtering access-list 100 deny ip 127.0.0.0 0.255.255.255 any log
access-list 100 deny ip 255.0.0.0 0.255.255.255 any log
access-list 100 deny ip 224.0.0.0 31.255.255.255 any log
access-list 100 deny ip host 0.0.0.0 any log
access-list 100 deny ip 10.0.0.0 0.255.255.255 any log
access-list 100 deny ip 172.16.0.0 0.15.255.255 any log
access-list 100 deny ip 192.0.2.0 0.0.0.255 any log
access-list 100 deny ip 192.168.0.0 0.0.255.255 any log
access-list 100 deny ip 14.0.0.0 0.255.255.255 any log
access-list 100 deny ip 169.254.0.0 0.0.255.255 any log
access-list 100 deny ip 198.18.0.0 0.0.255.255 any log
access-list 100 deny ip 66.238.29.0 0.0.0.31 any log
! no routing protocols inbound (unless needed) access-list 100 deny tcp any any eq bgp log
access-list 100 deny tcp any eq bgp any log
access-list 100 deny ipinip any any
access-list 100 deny gre any any
access-list 100 deny pim any any
access-list 100 deny 90 any any
access-list 100 deny ospf any any log
access-list 100 deny eigrp any any log
access-list 100 deny udp any eq rip any log
access-list 100 deny udp any any eq rip log
access-list 100 permit now begins your permits...if any
Notes: 192.0.2.0 0.0.0.255 any log (
range known to be used exploit default pw on WLA devices)
4.0.0.0 0.255.255.255 any log (
Known as Net-14, a Public use network, possibly used by attackers)
69.254.0.0 0.0.255.255 any log (
RFC2026 Link Local)
198.18.0.0 0.0.255.255 any log (
block for benchmark tests of network interconnect devices, RFC2544)
