Null routed

Additional uses for this same command are for route summarization, and route advertisements. This command above enters a route into the RIB Routing information base for the subnet in question.

This can be used to advertise a summary route from a router so any host looking for this particular network will be directed to the router that originates this null0 route. This same functionality can be used to test BGP advertisements. A prerequisite for advertising a BGP route is to have the IP range you wish to advertise in the routing table. This can be a powerful tool in any size network to eliminate unwanted traffic, and manipulate traffic in a simple, efficient way.

You are commenting using your WordPress. You are commenting using your Google account. You are commenting using your Twitter account. You are commenting using your Facebook account. Notify me of new comments via email. Notify me of new posts via email. Share this: Twitter Facebook. Like this: Like Loading Leave a Reply Cancel reply Enter your comment here A static route to Null0 is a normal static route, except that it points to the Null0 interface, which is a virtual IOS interface.

The next section presents an example of how to use the ip route command to create a static route to Null0. A common scenario where you may need to add a static route to Null0 is that of an access server which has many clients dialing in. This scenario causes host routes to be installed in the access server routing table. To ensure reachability to these clients, while not flooding the entire network with host routes, other routers in the network typically have a summary route which points to the access server.

In this type of configuration, the access server should have that same summary route pointing to the access server Null0 interface. If not, routing loops may occur when outside hosts attempt to reach IP addresses not currently assigned to a dialed in client but are part of the summary route.

This is because the access server would bounce the packets back over the access server default route into the core network, because the access server lacks a specific host route for the destination. In this example, the customer divided However, if packets are destined to network blocks which are not in use out of the This can have a huge impact on the router CPU and link utilization.

An example of where this traffic to unused IP addresses might come from could be denial of service attacks, scanning of IP blocks to find vulnerable hosts, etc. Note: We enabled some debug commands on the routers to better illustrate the packet flow, notably debug ip packet and debug ip icmp. Do not enable these commands in a production environment unless you fully understand the consequences. Router cust-R2 does not have a route to For example, if the ICMP request was for The solution to this problem is to configure a static route to Null0 for Note: There may be situations where the use of a summary static route to Null0 is not feasible.

For example, if in the previous example:. Note: The result would be that packets in transit or applications that attempt to reach this block of IP addresses create the same routing loop described earlier. Note: To fix this routing loop, you must use the ip route The in the command is the administrative distance.

Refer to What Is Administrative Distance?