I just took a practice exam and one of the sims I missed was due to the zero subnet. It stated that it wanted me to find the subnet mask with a max of 6 hosts. The IP range is 192.168.1.0 /24. Use the first available host on the first subnet for R1 S0 and the second available host on the first subnet for R2 S0. I came up with the mask /29 witch was correct and the first host address as 192.168.1.1. R2 S0 address was 220.127.116.11. I thought I was correct on those also. They said the correct first available host was .9 and the second was .10. In the explantion I finally understood the zero subnet deal but how do you know when it comes into play when they don't mention it in the question?
Somtimes you're the bug and sometimes you're the widshield.