Answers: IPv4 Static Routes 2

certskills
By certskills March 9, 2016 09:05

Want to know if you know IPv4 static routes well enough for the #CCNA exam? Practice til you know them so well that you can think the commands faster than you can type them. They’re a great learning tool for IPv4 routing! Check out the lab requirements, get some reps in, and solidify your knowledge of how IP routing works.

Answers

Figure 1: Four Switches with Trunks

Example 5: R1 Config

Example 6: R2 Config

Example 7: R3 Config

Example 8: R4 Config

 

Commentary

When configuring static routes, it is important to ensure that you have all of the correct IP subnet information because even a small difference in a subnet mask can make a big difference in routing behavior.

For this lab, you were tasked with configuring static routes between the routers so that each of their LANs would be able to route packets to each other. Because there are four different routes in this topology, this means that there will be three remote LAN subnets that need to have routes configured per router.

For R1, the three remote LAN subnets are: 192.168.100.64/26, 192.168.100.128/26, and 192.168.100.192/26. The first route would be for R2’s LAN, the common subnet between the routers uses the 172.16.100.0/24 network. R2’s IP address on this shared LAN is 172.16.100.2, making this address the next-hop address in the static route. The complete command to configure this static route would be ip route 192.168.100.64 255.255.255.192 172.16.100.2.

R1’s second static route, for the subnet off R3’s G0/2 interface, would use R3’s IP address on this shared LAN of 172.16.100.3. The complete command to configure this static route would be ip route 192.168.100.128 255.255.255.192 172.16.100.3.

R1’s third and final route would be for the subnet off R4’s G0/2 interface, with R4’s IP address on the central LAN of 172.16.100.4 as the next-hop. The complete command to configure this static route would be ip route 192.168.100.192 255.255.255.192 172.16.100.4.

R2 likewise has three static routes, one each for the three remote LAN subnets: 192.168.100.0/26, 192.168.100.128/26 and 192.168.100.192/26. Note that of the three commands in Example 6, one references R1’s address as next hop, one references R3’s address as next-hop, and one references R4’s address as next-hop. Take the time to look at the subnet ID and mask in each command, compared to the figure; you should see correlation, with R1 as next-hop for the route to the subnet off R1’s G0/2 interface, and so on.

Similarly, R3 has three static routes, referencing R1, R2, and R4 as next-hop routers for three different remote subnets. R4 also has three static routes, with R1, R2, and R3 as the next-hop routers.

IPv4 Static Routes 2
ROAS Basics 1
certskills
By certskills March 9, 2016 09:05
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6 Comments

  1. HectorJ December 23, 16:40

    What would happen if outgoing interfaces were used instead next-hop addresses?

    Reply to this comment
  2. abrakour May 11, 14:48

    We could just put Default Routes in each router (R1, R2, R3, R4) pointing to their respective interfaces (the ones “facing” the central switch and let ARP do the rest 🙂 .
    Let me know your opinion on my solution.

    (example using R1)

    R1(config)# ip route 0.0.0.0 0.0.0.0 G0/1

    By the way I tested it and it works. I can ping anything in the network with an max initial 3 ICMPs lost..

    Reply to this comment
  3. theurge14 February 20, 23:39

    Notice when you add static routes on the interface instead of the next hop, when you ping the other hosts they stay are added to your ARP table. Imagine a much larger network and how quickly your ARP table fills up with other hosts on other subnets. Doesn’t seem to scale well.

    Reply to this comment
  4. M.Asif June 21, 22:40

    Hello sir,

    I have setup the same topology in packet tracer. But may i know you just add the Lan SW between four Routers. May when I tried to ping from R1 to R2 172.168.100. 2 it does not ping also the same error from R2 to R3 or R4. I just add the connection between the Routers by using the 172.168.100.0/24. Please help me to fix this issue.

    Reply to this comment
    • CCENTSkills June 22, 10:18

      Hi M. Asif,
      Well, as a rule, I don’t comment on how simulators like PT work – that’s a question for your Networking Academy support channels, given that it’s a tool for Academy students. However, you question may just be a networking question.
      If you were using real gear, you could erase the config in the switch, and the switch should work. You also need to make sure that the routers each have enabled their interfaces that connect to the switch, and have the IP addresses configured. (It appears from your comments that you did configure the IP addresses on the routers.)

      In short, the switch just needs to configure all 4 ports as access ports in the same VLAN; they’ll all be in VLAN 1 by default with all default config.

      Maybe check to see if PT is leaving all switchports in a shutdown state to start, and if so, add a “no shutdown”.

      My $.02.
      W

      Reply to this comment
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