Boson Exam and zero subnet

MarkeyMarkey Member Posts: 14 ■□□□□□□□□□
Hello I'm new. Took CCENT last week and didn't make it 756 802 needed or something like that hmm is that how they base the number of the exam? Anyway...

The Boson exam environment comes with the Ciscopress ICND1 and 2 books by Wendell Odom. I've found quite a few mistakes in book one i.e. wrong diagrams left out items incorrect items etc.

Ch. 15 Table 2 lists the rules on when to use Zero Subnets and not. But what I'm finding is that the exam environment doesn't follow these rules. I've read on this forum that you should assume that if it's not mentioned on the official exam then assume subnet zero is in use. I am going to take the test again soon and want to make sure I have this right. I'm afraid that because I didn't (I did take the exam assuming the rules in table 15-2) I got some answers wrong.

Case in point in the Boson exam question # 107 (I'm only going to list the serial link because the question blows the rules on the ethernets also)

Problem statement:

The figure shows an internetwork, with IP addresses and default gateways for some devices. The addresses have been configured on the routers and the PCs have been configured using the same subnet masks as the routers on the LANs. A routing protocol has been enabled, and both routers have learned all routes known by the other router. Which of the following statements are ture about the behavior of IP in this network.

2 routers

Rtr 1:


Rtr 2:


the response

NO ip addresses are wasted on the serial links IP subnet

They list this answer as being one of the correct responses which really drives me crazy because no where in the problem statement is it expliciitly stated that No subnet zero or a classlful routing protocol is used.

My thinking is that the zero subnet and the broadcast should be available based on Odoms rules in table 15-2

Please correct me if I'm wrong here?


  • dtlokeedtlokee Member Posts: 2,378 ■■■■□□□□□□
    The classful network you are working with is, and if you subnet it using 6 additional subnet bits (/30). Subnet zer refers to the one with all 0's in the subnet portion of the address, or the first available subnet. In this case that would be The subnet here is which is the 5th available subnet.
    The only easy day was yesterday!
  • MarkeyMarkey Member Posts: 14 ■□□□□□□□□□
    Thanks for the response but that doesn't answer my question. Can you explain your repsonse further? I realize what you are saying to be true. But given the problem and the response (that is correct according to Boson) is the subnet address (zero subnet) available? According to Odom's rules the subnets are not reserved if the exam question says nothin about zero subnet use or classful routing.
  • MarkeyMarkey Member Posts: 14 ■□□□□□□□□□
    okay I think I may know where I'm going wrong here. After reviewing Odom's explanation again; The zero subnet like you say is the first address of the classful network in this case and the broadcast subnet is Which makes sense being the number of subnets is caculated 2^#subnet bits - 2.

    Where I've been going wrong is thinking that the 'subnet number' was actually the zero subnet and the subnets 'broadcast address' was the broadcast subnet.

    My apologies to Mr. Odom.
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