Answer Part 2: Subnet Design Exercise

By certskills July 6, 2011 09:00

Today’s post picks up the discussion of the solution to the subnet design exercise I posted a while back. Start with the post for the original problem statement, and read from there!

The third requirement stated that the WAN subnets should use the two numerically lowest subnet IDs. Without any reason to avoid it, the zero subnet ( should be used. So, the R1-R2 link will use that subnet, and the R2-R3 link will use

The fourth requirement states that the 3 numerically-highest subnets should be the R1 LAN, R2 LAN, and R3 LAN, in that order. Just pick those from the list. The final choices for the subnet then are:

R1-R2 WAN:

R1-R3 WAN:




To meet the firth requirement, you need to find the range of addresses in each subnet, which then tells you the last IP address in each subnet. The configuration at that point should not be a stretch. Examples 1, 2, and 3 show the resulting configuration on routers R1, R2, and R3.

Example 1: R1 Configuration

Example 2: R2 Configuration

Example 3: R3 Configuration

Answer (Part 1): Subnet Design Exercise
Subnet Design Exercise 2
By certskills July 6, 2011 09:00
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  1. Jason July 7, 03:24

    Thanks for this exercise.

    You have a coupe of typos: The IP address for interface s0/0/0 of R3 and multiple IP address configs for interface S0/0/1 of R2.

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  2. Peter L. June 16, 14:27

    This assumes that “ip subnet-zero” is not configured so /23 is unavailable. You didn’t show the prior config, so there was no way to guess. Thas setting is disabled by default but enabled in 99% of installations. Is that the kind of thing the exam is designed to trip us up on?

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  3. Bav October 4, 13:50

    Feels good to get these all right 1st time. Thanks for putting together this blog.

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  4. RN January 11, 05:25

    Hello Wendell,

    It seems that on R3 configuration, the interface should be S0/0/1 and not S0/0/0. (per the network diagram.)

    (It probably makes more sense to change the interface on the diagram rather than the configuration command.)



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