Answers: IP Addresses 2

certskills
By certskills March 26, 2016 12:05

Try a little subnetting math for a quick review, and add some IP address configuration – short, sweet, and just one more quick round of practice. Check out the initial requirements in this post, and come back here for the answers.

Answers

Figure 1: Four Switches with Trunks

Example 5: R1 Config

Example 2: R2 Config

Example 3: R3 Config

Example 4: R4 Config

Commentary

When configuring IP addressing information on a networking device, it is very important to ensure that the information is correct before putting a device into production. Unlike an IP overlap on a single PC which could affect that one device, or possibly affect another on the local subnet, the misconfiguration of an IP address on a networking device can affect whole LAN.

For this lab, you were tasked with performing the IP addressing configuration on the five subnets shown in the figure. Four of the subnets required that the router use the highest IP address in each subnet for the connecting interface, as follows:

  • R1’s LAN subnet uses the 172.16.1.0/27 subnet, the range of addresses including the subnet ID and broadcast address is 172.16.1.0 – 172.16.1.31, for a router interface address of 172.16.1.30.
  • R2’s LAN subnet uses the 192.168.1.64/28 subnet, the range of addresses including the subnet ID and broadcast address is 192.168.1.64 – 192.168.1.79, for a router interface address of 192.168.1.78.
  • R3’s LAN subnet uses the 10.20.30.168/29 subnet, the range of addresses including the subnet ID and broadcast address is 10.20.30.168 – 10.20.30.175, for a router interface address of 10.20.30.174.
  • R4’s LAN subnet uses the 10.100.45.192/26 subnet, the range of addresses including the subnet ID and broadcast address 10.100.45.192 – 10.100.45.255, for a router interface address of 10.100.45.254.

Additionally, all four G0/1 interfaces needed an address in subnet 172.16.100.0/24.

IP Addresses 2
Trunking Puzzle 1
certskills
By certskills March 26, 2016 12:05
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9 Comments

  1. Farrishan October 12, 20:10

    Wendell, do I need to set clock rate for routers interface gi0/1? I saw there is no CSU/DSU.
    Thanks

    Reply to this comment
    • CCENTSkills October 14, 17:03

      Hi Farrishan,
      Nope! CSU/DSU devices are unique to Time Division Multiplexing (TDM) physical links – serial, T1, E1, T3, E3, etc.
      Wendell

      Reply to this comment
  2. Abdi March 13, 12:45

    hi Wendell, can you please tell me when you say highest allowable IP address is that the number before the broadcast address? or is it the first number after the subnet ID

    Reply to this comment
    • CCENTSkills March 14, 10:59

      Hi Abdi,
      Yes, highest meaning numerically highest/larger. EG, in 10.1.1.0/24, with broadcast address 10.1.1.255, highest is 10.1.1.254, lowest is 10.1.1.1.
      Wendell

      Reply to this comment
  3. Abdi March 21, 05:39

    thanks wendell, i have done the excersice with 100% correct, but something that confuses me is when I am trying find out the resident subnet of an IP address do I have to keep incrimenting the subnet ID with the value calculated untill reached close, is there a quicker way, say if you have to increment 4 each time and you need to go as close as possible to a number say like 192, this will take long time in the exam, is there a quicker way to do it? thanks

    Reply to this comment
    • 4lban October 4, 09:09

      I’m interested in this question too.

      Reply to this comment
    • CCENTSkills October 4, 09:59

      Hi Abdi,
      Sorry, just saw your post because of 4lban’s message. I imagine you don’t care, but…
      I show some optimizations like you describe in a live course I teach on subnetting. It’s hard to do in a static text. But the idea is pretty basic:
      If the magic number is 2, 4, or 8…
      And you need to find a high magic multiple…
      count by 40’s until you get close: 0, 40, 80, 120…
      Why? Because 40 is a multiple of 2, 4, and 8.

      EG, to get to 211:
      0, 40, 80, 120, 160, 200… then go back to counting by the magic number.

      You can do the same with magic number 16 by counting by 80.

      Also, as an alternative, you can also just practice counting by 16 and 32 in your head, over and over, until you do that really fast. Then, for the smaller magic numbers, start by counting by 32’s or 16’s to get close, and then go back to counting by the magic number. Why? 16 and 32 are of cournse multiples of 2, 4, and 8, so all multiples of 16 and 32 are also multiples of 2, 4, and 8.

      Wendell

      Reply to this comment
  4. LT April 9, 06:17

    Referring to the Host Device Info table, PC2’s IP address is the same IP address of Gi0/2 on R2 according to the answers given above. We’ll need to assign a different IP address for PC2 in this subnet.

    Reply to this comment
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