Routing table: 2 subnets, 3 masks.

[Jhon_Cena_Fan619]

Sorry if this question is mundane, but I am confused over the 'subnet' and 'mask' information displayed in the routing table. For example [in image]:

The EIGRP network has 2 subnets and 2 masks, but for each directly-connected network there are 2 subnets and 3 masks. I understand where the subnets come from, but why 2 or 3 masks? Can someone explain this to me please?

Thanks!

[balaji.bandi]

As per your route output. it shows 2 subnets and found 3 different subnet masks found here.

can you explain and show us your configuration to undertand better.(also what is the device and what code of IOS is this ?)

[Jhon_Cena_Fan619]

It's a routing table example from Cisco Networking Academy:

However, I'm starting to think this might be a mistake (?), because what appears to be the exact same configuration is given here, two slides earlier or so:

[balaji.bandi]

May be fat fingers typo. 

[Deepak Kumar]

Hi,

This 3 mask seems some typo.

Let understand the routing table to make easy the process:

10.0.0.0/8 is variably subnetted, 2 subnets, 2 masks

In the technical word, above mentioned route is called  level 1 parent routes in the routing table of R1. The routing table basically provides a heading for the specific subnets it contains. Each entry displays the classful network address, the number of subnets, and the number of different subnet masks that the classful address has been subdivided into.

Means: class-full subnet 10.0.0.0/8 is divided into two classless routes as 10.1.1.0/24 and 10.1.2.0/24

 D   10.1.1.0/24 [90/2170112] via 200.165.200.226, 00:00:05, Serial 0/0/0

D= This route learned by EIGRP routing protocol.

10.1.1.0/24 = Actual Network which is learned

90 = EIGRP AD Value / 2170112 = Metric

200.165.200.226 = a next-hop IPv4 address for the route 10.1.1.0/24

00:00:05= How old this route 

Serial 0/0/0 = Existing interface for this route.

This route is called An ultimate route is a routing table entry that contains either a next-hop IPv4 address or an exit interface. Directly connected, dynamically learned, and local routes are ultimate routes. 

This will help you more:

http://www.ciscopress.com/articles/article.asp?p=2180210&seqNum=12

Regards,

Deepak Kumar