Routing entry for 192.168.0.0/16, supernet

[mahesh18]

                   Hi everyone,

I was tracing the router when i did sh ip route it shows

sh ip route 192.168.210.16

Routing entry for 192.168.0.0/16, supernet ********

  Known via "static", distance 1, metric 0

  Routing Descriptor Blocks:

  * 172.31.102.1

      Route metric is 0, traffic share count is 1

Need to understand what does supernet mean here?

does it indicate bigger subnet mask?

Thanks

Mahesh

[Gregory Snipes · Accepted solution]

Supernet is a nomenclature applied to a network witch is larger then should be allowed by the networks classfull boundary. In this case 192.168.X.X networks are Class C networks, the largest subnet you should be allowed to make of them is a /24 network. A /16 mask here is tying together 256 class C networks into one big supernet. Support for supernetting was introduced relatively recently.

[Edison Ortiz · Accepted solution]

Is the result of aggregating multiple subnets into one.

In your case, you are aggregating multiple Class C subnets into a larger address scope with the static IP route configuration implemented in the router.

[mahesh18]

Hi Edsion,

Thanks for answering the question.

Can you please tell me what is benefit of aggregating multiple subnets into one?

Regards

Mahesh

[Reza Sharifi · Accepted solution]

Hi Mahesh,

The main benefit of aggregating multiple subnets into one is fewer routes in the routing table.

For examle, instead of seen 4 /24 subnets, you just see one /22 subnet.

HTH

Reza

[Edison Ortiz · Accepted solution]

There are plenty of benefits. One comes to mind is scalability, less prefixes in the routing table = less memory consumption.

[mahesh18]

Hi Edison,

So we can say it is same as doing Auto  summarization in  EIGRP ?

When we do auto summ in EIGRP then also we have single route in routing table  instead of many right?

Thanks

Mahesh

[Richard Burts · Accepted solution]

Mahesh

The result of auto summarization is a single route (the "natural mask" network address - the class A or class B or class C network). aggregation is not necessarily going to produce a single route result.

I would suggest that aggregation and summarization are terms that mean the same thing. They both describe a process where we have a number of individual entries and we produce something with a smaller number of entries that include all of the addresses of the individual entries.

In addition to the benefits already given (smaller routing table, less memory) another possible benefit of aggregation/summarization is more stability in the routing table. Perhaps an example might help make clear what I mean. Think about a network that has 100 routers in it and that every router has 3 LAN subnets connected. If there is no aggregation/summarization then every router has a routing table with 300 entries. And assume that on one of the routers there is a problem with one of the subnets and the interface is flapping (it is up, and then it goes down, and soon it comes back up, but quickly it goes down again, and then it is up, and then down again, over and over). The result is that the other 99 routers are processing a routing update every time it goes down, and a routing update every time it comes up. So that is a LOT of routing updates.

Then think of that network and assume that each of the 100 routers does summarization of its LAN subnets and advertises one summary. Now the routing table of each router has 100 entries rather than 300. And now that subnet is flapping but there are no routing updates. The routing table is more stable because of the summarization.

HTH

Rick

[mahesh18]

Hi Rick,

Again your answer was pretty detailed  and its hard to find the knowledge you have   in books.

Best Regards

MAhesh