Black hole filtering is a technique usually used by service providers for traffic filtering without applying access-lists.
The technique is very useful in mitigation of many types of DOS attacks. The idea behind Black hole filtering is very simple; just define the traffic you want to discard and configure a static route pointing to the Null0 interface.
The following rules summarize the technique:
- Define the suspected traffic by destination.
- Configure static route pointing this destination to null0.
- Black hole filtering is based on the destination address of the packet.
- Packets directed to the Null interface are just discarded.
- Static routes to the Null0 interface use the same rules of normal static routes (redistribution, AD, etc..).
!-- packets destined to 192.168.1.1 are discarded ip route 192.168.1.1 255.255.255.255 null0 !-- Disable ICMP unreachable packets int null0 no ip unreachables