#CCNA Tshoot Drill: OSPF Hello Timer Changed

For this final variation of a #CCNA Simlet question in this series, consider what happens when one OSPF neighbor changes its OSPF Hello interval. Based on what you expect to change, what show command output should change? Prep for those Simlet questions again with today’s post (the question) and the following answer post.

Earlier posts in this series:

None, but there is a series that details the benefits and needs for these troubleshooting drills. Check this post for some comments about the usefulness of troubleshooting drills and how to create these for yourself.

Troubleshooting Drill Overview

All the troubleshooting drills begin with:

1. A topology diagram for the network
2. The correct working configuration for the relevant devices
3. The list of changes made to the configuration

Your job in these drills is to imagine that you have a Sim or Simlet question on the exam that uses the topology and configuration as described (including the changes). Then, focus on show commands, assuming that the exam did not let you look at the configuration at all. Then answer for yourself:

1. Which show commands will tell me relevant information in this scenario?
2. What will be different in the show command output, comparing the working configuration (after step 2), versus the output taken after making the configuration changes (after step 3)?

Setup: Topology and Working Configuration

This drill uses the same base topology and configuration as some other drills, with the details repeated here for convenience. The figure shows the topology:

Figure 1: Topology Diagram

The following three examples list the configuration for the three routers.

Example 1: R1 Configuration

interface FastEthernet0/0
 ip address 172.16.0.1 255.255.254.0
 duplex auto
 speed auto
 no shutdown
!
interface Serial0/0/0
 ip address 172.16.6.1 255.255.254.0
 clock rate 1536000
 no shutdown
!
interface Serial0/0/1
 ip address 172.16.8.1 255.255.254.0
 clock rate 1536000
 no shutdown
!
router ospf 1
 router-id 1.1.1.1
 network 172.16.0.0 0.0.1.255 area 0
 network 172.16.6.0 0.0.1.255 area 0
 network 172.16.8.0 0.0.1.255 area 0

Example 2: R2 Configuration

interface FastEthernet0/0
 ip address 172.16.2.2 255.255.254.0
 duplex auto
 speed auto
 no shutdown
!
interface Serial0/0/0
 ip address 172.16.10.2 255.255.254.0
 clock rate 1536000
 no shutdown
!
interface Serial0/0/1
 ip address 172.16.6.2 255.255.254.0
 no shutdown
!
router ospf 1
 router-id 2.2.2.2
 network 172.16.2.0 0.0.1.255 area 0
 network 172.16.6.0 0.0.1.255 area 0
 network 172.16.10.0 0.0.1.255 area 0

Example 3: R3 Configuration

interface FastEthernet0/0
 ip address 172.16.4.3 255.255.254.0
 duplex auto
 speed auto
 no shutdown
!
interface Serial0/0/0
 ip address 172.16.8.3 255.255.254.0
 clock rate 1536000
 no shutdown
!
interface Serial0/0/1
 ip address 172.16.10.3 255.255.254.0
 no shutdown
!
router ospf 1
 router-id 3.3.3.3
 network 172.16.4.0 0.0.1.255 area 0
 network 172.16.8.0 0.0.1.255 area 0
 network 172.16.10.0 0.0.1.255 area 0

Note that while the PC can be assigned IP addresses and default gateway values, they do not matter to this exercise.

Configuration Changes for this Troubleshooting Drill

For this drill, imagine the scenario has been implemented as described so far in this blog post. Then, the configuration is changed, as follows:

R1: Interface S0/0/1’s OSPF Hello interval is changed to 11 seconds. That is, the configuration commands interface s0/0/1 and ip ospf hello-interval 11 are issued in sequence.

Your Tasks

Your tasks are relatively straightforward, as follows:

1. Think, without your notes. What commands identify relevant information about this scenario? Make a list of the commands. Then look at your notes to complete your list.
2. Which of those will have different information due to this change? Which will show no differences? For those whose output changes, what changes do you expect to see?