Answers: IPv6 Static Routes 1

certskills
By certskills April 28, 2016 09:10

Planning for and configuring static routes may be one of the best tools for learning how layer 3 routing works. Check out the lab requirements for this lab, create your own configuration for this lab, and come here to check your answers. While you’re at it, predict the IPv6 addresses that would be listed if sitting at PC’s 1, 2, and 3 and issuing a traceroute6 command for the other PC’s IPv6 addresses.

Answers

Figure 1: Simple Hub and Spoke Topology

Example 1: Core Config

 

Example 2: Branch1 Config

 

Example 3: Branch2 Config

 

Example 4: Branch3 Config

 

Commentary

When configuring static routes, it is important to ensure that you have all of the correct IPv6 subnet information, just a little difference in subnet mask can make a big difference in routing behavior.

For this lab you were tasked with configuring static routes to all remote subnets on all routers. The figure shows six different subnets. The Core router connects to three subnets, so it will need three static routes. Each branch router connects to two subnets, so each branch router will need static routes for four different subnets.

For Core, the three remote LAN subnets are 2000::/64,2001::/64 and 2002::/64. Just to help us get our bearings, Table 1 lists the three destination subnets, with router Core’s outgoing interface and next-hop global unicast address:

Destination Subnet Off of Router… Core’s Outgoing interface Core’s Next-Hop Address
2000::/64 Branch1 G0/1 3000::2
2001::/64 Branch2 G0/2 3001::2
2002::/64 Branch3 G0/3 3002::2

Table 1: Data to Use in Router Core’s Static IPv6 Routes

 

The configuration, shown in Example 1, repeats the ipv6 route command three times. Each time it lists the destination subnet per the first column of the table, and the next hop address per the last column. For example, the complete command to configure one static route would be ipv6 route 2000::/64 3000::2.

For Branch1, before thinking about the configuration command, think about the topology in the figure. Branch1 has two connected subnets. Then, to send packets to the other four subnets, router Branch1 will always send the packets out its G0/1 interface to the Core router next. As a result, and as seen in Example 2, all four of Branch1’s routes list 3000::1 as the next hop address. The four commands each list a different destination subnet: 3001::/64, 2001::/64, 3002::/64 and 2002::/64.

Branch2 uses the same basic logic as router Branch1. Branch2 has two connected subnets, four remote subnets, and all four static routes for the remote subnets points to router Core next. In Branch2’s case, the next-hop address of the Core router is 3001::1. As seen in Example 3, the four ipv6 route commands list 3001::1 as the next-hop address, with subnets 3000::/64, 2000::/64, 3002::/64 and 2002::/64 in the four different commands.

As you probably guess by now, Branch3 uses the same basic logic as routers Branch1 and Branch2. Branch3 has two connected subnets, four remote subnets, and all four static routes for the remote subnets points to router Core next. In Branch3’s case, the next-hop address of the Core router is 3002::1. As seen in Example 4, the four ipv6 route commands list 3002::1 as the next-hop address, with subnets 3000::/64, 2000::/64, 3001::/64 and 2001::/64.

Answers: GRE Tunnel 1
IP Addresses 1
certskills
By certskills April 28, 2016 09:10
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6 Comments

  1. Gabriel Lopez March 27, 16:33

    I don’t need to enable ipv6 routing with the
    ipv6 unicast-routing command?

    Reply to this comment
    • CCENTSkills March 30, 10:21

      Hi Gabriel,
      In an odd quirk: no. That command actually enables the use of IPv6 routing protocols in practice, even though IOS doc claims that it enables the IPv6 layer 3 forwarding processes.
      Wendell

      Reply to this comment
      • Bav March 25, 09:12

        When labbing this in packet tracer I found that if I wanted to set the hosts to use auto address assignment, then without the ipv6 unicast-routing command, the routers would not respond to any router solicitation messages.

        Is this typical of real world behavior?

        Reply to this comment
        • CCENTSkills April 3, 10:35

          Hi Bav,
          Yes indeed. The “ipv6 unicast-routing” command enables IPv6 routing on the router, making it act like a router… which includes replying to NDP Router Solicitation (RS) messages with a Router Advertisement (RA) message. Spot on.

          Reply to this comment
  2. vitylobo June 5, 06:07

    Hi Wendell,
    can we use static default route for Branch routers here? I assume that a static default route is also a static route as per question requirement.
    This way we have to configure only one static default route on each Branch router. Something like:

    Branch1:
    ipv6 route ::/0 3000::1

    Branch2:
    ipv6 route ::/0 3001::1

    Branch3:
    ipv6 route ::/0 3002::1

    Appreciated your feedback.

    Reply to this comment
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