Is a summary Null0?
The answer is no. In conclusion, a summarized route to Null0 interface is created along with the summarization of that route. If the summarizing router does not have a specific route for a subnet of that summarized route, it will send packets to Null0, sometimes called a “black hole”.
Why is Null0 used in summary route?
The purpose of configuring a static summary route to null0 is to make sure that traffic will be dropped on the local router if a more specific route doesn’t exist.
Does OSPF Auto summary?
Route summarization helps reduce OSPF traffic and route computation. OSPF, unlike EIGRP, doesn’t support automatic summarization. Also, unlike EIGRP, where you can summarize routes on every router in an EIGRP network, OSFP can summarize routes only on ABRs and ASBRs.
What is interface Null0?
The null0 interface is primarily used when a router advertises a summary address. The idea is that this router has all the more specific routes and so if a packet is received for which the router has no matching route, rather than forward the packet on and potentially creating a routing loop, the packet is dropped ie.
What is the purpose of the Eigrp Null0 summary route?
What is the purpose of the EIGRP Null0 summary route? To prevent routing loops for destination networks which do not actually exist but are included in a summary route.
What is a Null0 route?
A null route or blackhole route is a route for an IP address that goes nowhere. The reason for creating a null route for your IP address is to prevent your server from receiving or sending any data over the Internet.
What is the purpose of Null0?
Null0 is a virtual interface that is a route to nowhere and is used to prevent routing loops for destinations that are included in a summary network but do not have a specific entry in the routing table.
What is the Null0 interface Cisco router?
The null interface is the “bit bucket” or “black hole” interface. All traffic sent to this interface is discarded. It is most useful for filtering unwanted traffic, because you can discard traffic simply by routing it to the null interface.
What is the null0 interface used for?
The Null interface is typically used for preventing routing loops. Enhanced Interior Gateway Routing Protocol (EIGRP), for instance, always creates a route to the Null0 interface when it summarizes a group of routes. Whenever a routing protocol summarizes, this means that the router might receive traffic for any IP address within that summary.
What is the difference between OSPF redistribution and discard route?
This is internal to the OSPF domain which is why this works, whereas the redistribution is redistributing from outside the ospf domain and the discard-route external only works with those. 08-13-2012 10:35 PM 08-13-2012 10:35 PM
What is a static route to null0?
A static route to Null0 is a normal static route, except that it points to the Null0 interface, which is a virtual IOS interface. Refer to the IP Routing Protocols Commands: I section of Cisco IOS IP Command Reference, Volume 2 of 4: Routing Protocols, Release 12.3 for more information about the ip route command.
Why doesn’t EIGRP auto-summarize a route to null0?
If EIGRP is auto-summarizing it will only install a route to Null0 if the subnet mask used on the advertising interface is not the classful subnet mask. For example: