Subnet Design Exercise 3
The subnet design exercises require that you do some subnetting math, but rather than reacting like you would in a help desk or support job role, you plan as if you were in the role of a lead network engineer. If you have seen the other subnet design exercises, you already know the drill. If not, read below the fold. The short version: you get some exercise in choosing the best subnet mask based on requirements, and then in finding all subnets, and choosing the best subnets to use, again based on a list of requirements. Answer to follow in a later post. Here are some helpful links:
- The ICND1 Cert Guide, where Chapters 16 and 18 help you find the answers
- All the Subnet Design Exercises in this Blog
Problem Statement
You need to design and pick subnets for the following small internetwork:
Figure 1: Network Diagram and Requirements
Note that the figure lists the requirements for the number of hosts per subnet, plus the fact that you must plan for 20% growth in the numbers of hosts per subnet on the LANs. Additionally, follow these requirements as well:
- The LAN subnets should come from class B network 172.24.0.0.
- The WAN subnet should also come from class B network 172.24.0.0.
- Choose 1 mask per classful network, and only one mask, to be used for all subnets
- For each classful network, choose the 1 mask that meets the requirements while using the least number of host bits
- Assign the WAN subnets as follows: give the R1-R2 links the numerically lowest subnet ID, the R2-R3 link the next lowest, and the R1-R3 link the next lowest.
- Assign the LAN subnets with the three numerically highest subnet IDs; R1’s LAN with the highest, R2’s LAN next, and then R3’s LAN.
- Choose IP addresses for the router as the highest IP addresses in each subnet.
- On the WAN links, which have mlutiple router IP addresses in one subnet, give the highest IP address to the router with the higher router number (eg, R2 gets a higher IP address than R1).
I believe those requirements paint you into a corner well enough so that there is only one solution; if not, and my solution is different than yours, but you think yours is also valid, feel free to post. Also, post any clarifying questions you like before I post the answer.
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