is mask 255.255.255.10 valid ?

[sumerfat]

I was trying this example :

https://routersimulator.certexams.com/router-labs/router-interface-configuration.html

for the serial it shows invalid interface type and number, how can I solve this ?

for the fa it shows invalid mask , why are they putting mask ends with 10, and 5 in that example, is it valid ?

[MHM Cisco World · Accepted solution]

Nop that mask is wrong both of them .5 and .10,

Some example in wrong.

You  are right.

Note:- i trt in gns3 and both mask is refuse by router with log

""Bad mask""

[Elliot Dierksen]

These are the valid values for an octet in a subnet mask: 255, 254(sometimes), 252, 248, 240, 224, 192, 128, 0. Other than 255, you are subtracting a power of 2 from 256 to get the valid values.