As with all the Config Labs with “BIG” in the title, this lab is different than most. This BIG lab collects many of the configuration topics in Volume 1, Part 6 of the CCNA Official Cert Guide, and lets you configure them. For this lab, you have a great opportunity to review VLAN, VLAN trunking, IP addressing, and interface configuration to understand the lab’s initial state. Then you enable OSPF on seven different routers. The lab gives you some parameters, leaving you to determine the configuration. In some cases, the lab asks you to decide which optional OSPF features to use.  Finally, you should verify each feature while configuring – you’ll learn as much by verifying OSPF as you do by configuring it. Enjoy!

The first task, which is fairly large, is to understand the topology and initial configuration. At this point in your studies, you should be comfortable navigating the Cisco CLI. So rather than placing large amounts of config here in this post, your job is to take a guided tour of the configuration in Cisco Packet Tracer. You can also watch my lab intro video on YouTube, where I walk you through the initial state.

So download the .pkt file, open it, and start systematically using show commands. Refer to Figure 1, and then work through the list that follows the figure.

Figure 1: Lab Topology

Use this list of discovery tasks to learn about the initial state of the lab. The list refers to each major step as a “Discovery”, with the configuration tasks that follow labelled as “Tasks”.

Discovery 1: Explore the pre-configured Core LAN

1. 1. Look to the left side of the figure for switches A1 (Access1), A2 (Access2), D1 (Dist1), and D2 (Dist2).
   2. A1 and A2 act as access switches, with access ports in VLANs 101 and 102.
   3. VLAN trunks exist between each access switch and each of the two distribution switches (D1 and D2).
   4. On the far left, the PCs and servers use static IPv4 settings to avoid the oddities of DHCP in Cisco Packet Tracer (CPT).
   5. The distribution switches perform layer 3 switching and, together, act as the default gateway for each LAN-based subnet, using HSRP to share those duties.
   6. Use the switch CLI and PC command prompts to explore and get comfortable with the VLANs, VLAN trunks, and IP addresses of the devices. (See upcoming reference tables.

Discovery 2: Explore VLANs 101 and 102 and the D1/D2 Matching VLAN Interfaces

1. 1. Identify the access ports in each VLAN (on the access switches).
   2. Identify the operating VLAN trunks.
   3. View the SVIs (VLAN interfaces) on both D1 and D2.
   4. Note the configured IP address and mask, and calculate the subnet ID and the address range for each subnet.

Discovery 3: Explore the Default Gateway settings and standby commands on D1/D2.

1. 1. On a few PCs and servers, note the preconfigured default gateway settings, which should point to addresses that end in .10.
   2. Examine the configuration on both D1 and D2, for the VLAN interfaces. Note the addresses configured with the ip address commands. What is the last octet of those addresses?
   3. Notice the standby command under each VLAN interface, which defines the IP address used as the default gateway for hosts in that subnet. Note that the standby commands define the IP address that serves as the default gateway for each subnet. Note that when HSRP is in use, addresses configured with the ip address subcommand will not be used as the default gateway.

Discovery 4: Explore Layer 3 LAN Links and Settings

1. 1. On the far left, revisit the VLAN interface IP addresses and masks on D1/D2. Make sure you know the subnet IDs and masks of those two subnets.
   2. Envision the upper right of the figure as branch 1, with two routers. Routers B11 and B12 both connect to the same LAN switch, to the same VLAN, where another subnet resides. Find the subnet/ID and mask for that subnet.
   3. Router B12 has some embedded LAN switch ports. Review the related configuration to find the VLAN, SVI, and subnet ID.
   4. Router B21 resides at a separate branch – think of it as branch 2 – with one LAN switch and VLAN. Learn about the VLAN on the switch and the subnet used on that VLAN.

Discovery 5: Examine Layer 3 Transit Links

1. 1. OSPF refers to links between routers, which are not typically the destinations for user traffic, as transit links.
   2. Next, focus on the six WAN links between the Core site and a branch router. Discover the IP subnet and mask used in each case.
   3. Then look at the three layer 3 links in the LAN core at the central site and identify the subnets in use.
   4. Spot check connectivity by pinging the IP addresses on either end of any of these WAN links. Note that OSPF and static routes are not preconfigured, so pings will only work for addresses in a connected subnet, such as a neighboring router.

Discovery 6: Check the Internet Link

1. 1. Router Core1 connects to an ISP router, so you can test a default route in OSPF. The ISP router and the ISP’s web server are preconfigured, but router Core1’s default route configuration is incomplete; this is a task for you in this lab.
   2. Discover the subnets used on the links connected to the ISP1 router. Note that the addresses that begin with 198 are represent public IPv4 addresses for the purposes of this exercise.

The following table lists the preconfigured IP addresses for the hosts in the lab.

Table 1: Hosts Used for Ping/Trace Tests

This lab organizes the work into six tasks. Some tasks require configuration on all routers, some on a few routers, and one task requires config on a single router. It’s up to you to examine each task, choose the required configuration for each device, configure the devices, and test the features to confirm they work.

You should pause and test the function of each task. For instance, in task one, you enable OSPF on all relevant interfaces in the topology, all in area 0. All routers should learn routes for all subnets in network 10.0.0.0 as a result. You should be able to examine IP routing tables in each router and confirm each router knows routes to each subnet.

Figure 2 repeats the earlier figure, just to reduce scrolling, with the configuration tasks detailed under the figure.

Figure 2: Lab Topology

Your lab tasks:

Task 1: Enable OSPF, in Area 0, and Configure Router IDs

1. 1. Enable OSPF on routers.
   2. When this lab refers to “routers”, that includes layer 3 switches – any device that performs routing.
   3. All links are in area 0.
   4. Assign router IDs per Table 2 (found after the task list). Use any config method you like.
   5. For variety, for the four routers at the core site (Dist1, Dist2, Core1, Core2), use network commands but no interface subcommands to enable OSPF on interfaces. For the network commands, you have two style options:
      1. You choose the number of network commands, you choose the wildcard masks, and make it work.
      2. Challenge: Use only one network command per router. You may only use wildcard masks with 0’s and 255’s, and use as few 255’s as possible to achieve the goal.
   6. For variety, use interface subcommands, but no network commands, on the branch routers.

Task 2: Tune OSPF Metrics

1. 1. Note that all physical interfaces in the topology happen to use 1 Gbps.
   2. Adjust the OSPF reference bandwidth to 100 Gbps.
   3. Influence routes that use WAN links to prefer routes to/from Core1, rather than Core2, by:
      1. Double the cost on both ends of the three WAN links that connect to Core2.
      2. Clarification: That is, after changing the reference bandwidth, determine the cost the router could calculate, and configure to override that metric with twice what the router would use.

Task 3: Use a Default Route to Send Traffic into the Internet

1. 1. Note: the ISP1 router is pre-configured with all required commands.
   2. On router Core1, configure a static route to forward all traffic that is not matched by any other route to the neighboring router ISP1.
   3. Configure OSPF as needed so that all routers learn a default route with OSPF.

Task 4: Tune LAN OSPF Hello and Dead Intervals

1. 1. Change the OSPF intervals on the various LAN interfaces as follows:
      1. Hello: 5 seconds
      2. Dead: 15 seconds
   2. For the purposes of this lab, “LAN interfaces” are those shown in the figure, connected to the yellow and blue rectangles, with the subnet IDs listed. They include: The VLAN interfaces in Dist1 and Dist2, the Go/o interfaces in B11, B12, and B21, and the VLAN interface in B12.

Task 5: Choose and Enable Good OSPF Passive Interfaces

1. 1. Some router interfaces can be made passive, without breaking neighbor relationships. Some cannot. Choose which router interfaces can be made passive without breaking any neighbor relationships.
   2. Configure those interfaces as passive to OSPF.

Task 6: Migrate from Broadcast to Point-to-Point network type

1. 1. On the six WAN links, on both ends, configure the routers to use point-to-point network type instead of broadcast.
   2. On the three routed links between Core1, Dist1, Dist2, and Core2, think about whether you would also want to use point-to-point on those links.
   3. If you decide you like the idea, also migrate to use point-to-point on the routed links at the core site.

The following table lists the router IDs (RIDs) to configure in lab:

Table 2: OSPF RIDs in Lab

The best way to learn about OSPF is to explore each feature after each task. I can suggest a few approaches to do just that:

1. Use your own skills and knowledge, and exercise those skills, to verify that the features in each task work.
2. Use the following list of suggested commands and actions to verify the features.
3. Use my YouTube lab review video. The video breaks down the discussion into the six major tasks, first showing the suggested configuration and then demonstrating how to verify that the feature works.

Below is a list of suggested verification actions to verify the OSPF features for each task.

Note: You will learn a lot doing these verification steps! But when you want a little help, watch the lab review video at the bottom of this post. Use the video chapters feature to find the demo for the specific task you’re interested in!

Verify 1: Check Neighbors, Interfaces, OSPF Routes

1. 1. When this lab refers to “routers”, that includes layer 3 switches – any device that performs routing.
   2. Think about the lab topology, focusing on the seven routers. Predict which routers should be OSPF neighbors with which other routers. Draw it, listing the RIDs beside each router.
   3. Use show ip ospf neighbor on each router to confirm all the neighbor relationships exist.
   4. Use show ip ospf interface brief on each router to confirm you enabled OSPF on all the expected interfaces. You may find the show ip interface brief command useful in comparison.
   5. Confirm all routers have routes to the LAN subnets, that is, the five subnets whose subnet IDs appear on this blog page.
      1. Use show ip route ospf to see only OSPF-learned routes.
      2. Spend some time considering the details of those routes, particularly the metrics and outgoing interfaces. Those will change in Task 2.
   6. For transit subnets – subnets with no endpoints, but only routers – you can examine the routes. All routers should have routes for those as well, but you can ignore them for this lab.

Verify 2: Verify Configured Settings and Route Metrics

1. 1. First, verify what you configured, starting with the reference bandwidth.
      1. You can only see it with the show running-config command, looking in OSPF config mode.
      2. It should be configured to a setting of 100000, on ALL the routers.
   2. For the task to override the default cost on some links:
      1. On links running at 1 Gbps, the calculated OSPF metric will be 100.
      2. So, you should have configured ip ospf cost 200 on both ends of the three WAN links that connect to Core2.
      3. On the routers on both ends of the link, use show ip ospf interface and show ip ospf interface brief to confirm the default cost of 100 and the configured cost of 200 as appropriate.
   3. Examine the routes to each LAN subnet (five of them) from Core1.
      1. Predict the cost of the route, calculated as the sum of the costs of the outgoing interfaces in the route.
      2. See that Core1 has cost 200 routes to two branch subnets (10.1.10.0/23 and 10.1.14.0/23).
      3. However, because of a quirk in Cisco Packet Tracer (CPT), you will see a much higher cost of 1100 to subnet 10.1.12.0/23 (the other branch subnet.)
      4. You will also see a cost 1100 route to the core site LAN subnets, due to the same CPT quirk (next topic).
   4. On Dist1, Dist2, and B12, investigate the odd CPT behavior that made those few routes have a much higher metric.
      1. CPT assigns a default bandwidth of 100,000 (Kbps) to the VLAN interfaces on these routers.
      2. The OSPF calculated metric, with a reference bandwidth of 100,000 (Mbps), is 1000.
      3. For instance, if using real Cisco switches for Dist1 and Dist2, the VLAN interfaces would have a default bandwidth of 1,000,000 Kbps, with the cost calculated as 100.
      4. The higher cost routes are not causing a problem. You could choose to change the costs using configuration if you like. I’m just letting you know about why it is happening.

Verify 3: Examine the OSPF-Learned Default Routes

1. 1. Start on Core1 and verify the static default route.
      1. Ping the www-isp server’s address (198.51.100.2) to confirm the route works. Also, try a traceroute to the same address.
      2. Display the IP routing table (show ip route) to see the presence of the “Gateway of Last Resort” and the default route (0.0.0.0/0) in the routing table.
   2. Select a few routers – at least one at the core site and one branch router – and examine the OSPF-learned default route on those routers.
      1. Display the IP routing table (show ip route) to see the presence of the “Gateway of Last Resort” and the default route (0.0.0.0/0) in the routing table.
      2. Note the origin (far-left code) on the route to 0.0.0.0/0.

Verify 4: Check OSPF Timers

1. 1. The “LAN” interfaces in the topology, as described on this page, are interfaces connected to the five subnets whose subnet IDs are shown in the figure. Those include:
      1. Interface VLAN101 and VLAN102 on both Dist1 and Dist2
      2. B11, B12, and B21’s G0/0 interfaces
      3. B12’s VLAN202 interface
   2. Examine the OSPF  interval settings on those interfaces:
      1. For physical interfaces, you can use show ip ospf interface g0/0 and show ip ospf interface brief.
      2. Due to a CPT quirk, for VLAN interfaces, you will need to use show ip ospf interface, and scroll a bit, or show ip ospf interface brief.
      3. You should look for a Hello of 5 and Dead interval of 15.

Verify 5: Identify and Confirm OSPF Passive Interfaces

1. 1. Think again about where you could have used OSPF passive interfaces in this lab topology:
      1. Not on the WAN links. Those are transit links (links with two or more routers) that need to send Hellos to establish and maintain neighbor relationships.
      2. Not on the three routed links between Core1-Dist1, Dist1-Dist2, and Dist2-Core2 – for the same reasons.
      3. Additionally, three LAN subnets have two routers connected to them. Those include the two core subnets (10.0.101.0 and 10.0.102.), and the Branch 1 subnet 10.1.10.0/23. If you make those routers passive, they will not become OSPF neighbors on those LAN links.
      4. Only B12, on its VLAN interface, and B21, on its LAN (G0/0) interface, can be made passive without breaking an OSPF neighbor.
   2. Check your configuration of passive interfaces on B12 and B21:
      1. Use show ip protocols, and look for the list of passive interfaces, for VLAN202 (B12) and G0/0 (B21).
      2. Use show running-config, and look for the OSPF configuration near the bottom of the output.

Verify 6: Confirm Neighbors on Links with OSPF Point-to-Point Network Type

1. 1. For this task, you made many changes across different interfaces, which could cause neighbor issues. Verify that you changed the network type on all interfaces on all routers on the link so the neighbors will still work.
   2. Start on Core1 with this approach:
      1. Use show ip ospf neighbor to confirm neighbor relationships w/ B11, B12, B21, and Dist1.
      2. Confirm that the neighbors are not using a DR based on the absence of notations about a DR or BDR.
      3. Use the show ip ospf interface brief command with the STATE column to confirm which interfaces now use network type point-to-point.
      4. Confirm the use of point-to-point using the show ip ospf interface g0/0/0 command or similar.
   3. Follow that same pattern of commands on Core2, B11, B12, and B21, and on Dist1 and Dist2 as needed.