How a route to Null0 works in EIGRP?

[roberto siu]

http://www.siunetworks.com           

[roberto siu]

OK, so When doing route summarization with some of our different routing protocols, you may have noticed that some of them will always add the summary route they are advertising downstream to the local routing table.  What is confusing at first to some is that this local summary route is given a next-hop of null0, also known as the bit bucket.  For example, if you are running EIGRP on a router and you configure a summary route like

ip summary-address eigrp 1 10.10.0.0 255.255.0.0 on an interface of that router you will see a route inserted into the routing table for 10.10.0.0/16 pointing to null0.

My question is:

How a route to Null0 works in EIGRP?

[roberto siu]

Ramon G. Said:

Oct 15, 2013 9:48 PM (in response to ROBERTOSIU CCNA R and S.)

Helpful AnswerRe: How a route to Null0 works for EIGRP?

HI Robert this explanation may help you:

[The Null0 summary interface is:]

"Another mechanism to prevent routing loops. EIGRP always creates a route to the Null0 interface when it summarizes a group of routes. This is because whenever a routing protocol summarizes, the router might receive traffic for any IP address within that summary. Since not all IP addresses are always in use, there is a risk of looping packets in case default routes are used on the router which receives the traffic for the summary route."

[Julio Carvajal · Accepted solution]

Hello Roberto,

I have answered you via email.

Here is my explanation for any user also looking this info

A null interface is basically a trash, whatever you send to a null
interface is the same as dropping the traffic.

You might be asking.

Okey so why when I perform route summarization on an EIGRP router this
route automatically gets created.

Well Robert, the whole purpose of route summarization is basically to
advertise a summary prefix to all or some specific neighbors based on our
routing process information; so as we can see the summary should affect
our neighbors not ourselfs, so this is why we point that.

What the route says is basically:
Do not install a route with this prefix, only installed more specific routes.

Does it make sense?

Regards,

Jcarvaja

http://laguiadelnetworking.com

[Julio Carvajal · Accepted solution]

Hello Roberto,

Please mark the question as answered if you do not have any other question,

Regards