OSPFv3 Costs and Multipath

By Chris December 7, 2015 09:05

This latest #CCNA CLI lab catches a variety of small items for OSPFv3 in an IPv6 network. Starting from a pre-configured set of routers with IPv6 addresses, this lab asks you to get OSPFv3 working, use specific router IDs, change the OSPF costs in a couple of different ways, and to change the number of equal-cost routes allowed in the IPv6 routing table. Check out the requirements below the fold!


First, enable OSPFv3 in this network, a network for which the IPv6 addresses have already been configured. Additionally, you will further customize the OSPFv3 configuration, by changing the OSPFv3 interface costs in a couple of different ways, and setting the number of equal-cost routes allowed.

The specific rules for this lab are:

  • Enable OSPFv3 on all the routers for all interfaces shown in the figure
  • Place all interfaces in area 0
  • Limit the maximum number of load-balanced paths on R1 to 1
  • Directly configure the OSPFv3 cost on both ends of the link between R2 and R4 to a value of 10
  • Indirectly configure the OSPFv3 on both ends of the link between R3 and R4 to a value of 10 by changing the link bandwidth
  • Directly configure (without relying on interface IPv4 addresses) an obvious OSPFv3 router ID for each router, for instance, use for router R1


Figure 1: Four Router with Unicast IPv6 Addresses


Initial Configuration

Examples 1, 2, 3 and 4 show the beginning configuration state of R1, R2, R3 and R4.

Example 1: R1 Config

Example 2: R2 Config

Example 3: R3 Config

Example 4: R4 Config


Answer on Paper, or Maybe Test in Lab

Create your own answer, either by typing it in somewhere, or writing it on paper. Try to avoid using your notes – one of points of these labs is to move you from being able to read someone else’s config to being able to create your own from scratch.

You can easily test this lab with a few show commands. First, each router should have two OSPFv3 neighbors (show ipv6 ospf neighbor). Then go to each router and check the OSPF cost on each interface (show ipv6 ospf interface brief). In this case, R1 and R4 should learn two equal-cost routes using OSPF for the subnets on the opposite side of the topology. If you configured correctly, R1 should list only one of those routes (to 3500::/64, with show ipv6 route), and R4 should list both routes (to 3000::/64, with show ipv6 route).


Do this Lab with Cisco’s VIRL

You can do these labs on paper and still get a lot out of the lab. As an extra help, we have added files for the Virtual Internet Routing Lab (VIRL) software as well. The .VIRL file found here is a file that when used with VIRL will load a lab topology similar to this lab’s topology, with the initial configuration shown in the lab as well. This section lists any differences between the lab exercise and the .VIRL file’s topology and configuration.

Download this lab’s VIRL file!


Network Device Info:

The .VIRL topology matches this lab topology exactly. The host info does as well.


Handy Host Commands:

To see PC IP address: ifconfig eth1

Ping example: ping6 -c 4 2001:DB8:1:1::100

Trace example: tracepath6 2001:DB8:1:1::100

Answer: Basic Port Security 3
Answers: OSPFv3 Costs and Multipath
By Chris December 7, 2015 09:05
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