Thank you, i will go through on this. But the first one is still mystery ..:-)
I went through one pdf, to check the wild card mask vs subnet mask. but there also its not differentiating the concept. this pdf saying the use of wild card mask. if we are using subnet mask in that place, we will get the same result. I have attached the same here.
But still I am confused, both are doing the same function ? 
manu_nambu wrote:
Thank you, i will go through on this. But the first one is still mystery ..:-)
I went through one pdf, to check the wild card mask vs subnet mask. but there also its not differentiating the concept. this pdf saying the use of wild card mask. if we are using subnet mask in that place, we will get the same result. I have attached the same here.
But still I am confused, both are doing the same function ?
I suspect there may be a couple of things going on here -
1) the subnet mask is often easier for people to understand and so it is an ease of use function that Cisco have put into the IOS. I also suspect there are many lines of EIGRP code that use the wildcard mask and expect to find a wildcard mask. So rather than have to translate the subnet mask to a wildcard mask every time the EIGRP code needs to deal with the "network" entries, a one off conversion is done when it is originally entered into the configuration.
This would then mean that all the other parts of the EIGRP code could simply use the mask involved without having to worry whether it was subnet or wildcard mask format.
2) Generally speaking a subnet mask must be contiguous whereas a wildcard mask does not have to be so you can be far more flexible with wildcard masks in specifying networks. However with EIGRP and OSPF the wildcard mask must also be contiguous when using it under the "router
Both of the above are best guesses.
Jon
