Configuring IPv6 Static Routes

The Foundation of IPv6 Routing

Before a router can forward any IPv6 packets between different networks, two things must be true:

1. The global command ipv6 unicast-routing must be enabled. As we saw in previous lessons, this command activates the entire IPv6 routing process on the device.
2. The router must have a path to the destination network in its IPv6 routing table, which you can view with show ipv6 route.

While we previously saw how a default route can be learned automatically via SLAAC, static routing involves manually creating these entries. This provides explicit control but requires manual updates if the network topology changes.

The video below offers an excellent introduction to IPv6 static routing. It clarifies how IPv6 routing, while conceptually similar to IPv4, operates as a separate process with its own routing table. It also introduces the different ways a static route can be defined.

Methods for Defining a Static Route

As the video explained, there are three primary ways to define an IPv6 static route based on what information you provide about the next hop.

• Recursive Static Route: You specify only the next-hop router's Global Unicast Address (GUA). The router must perform a recursive lookup—a second search in its routing table—to find which interface to use to reach that next-hop address.
  ipv6 route 2001:DB8:0:3::/64 2001:DB8:0:12::2

• Directly Attached Static Route: You specify only the local router's outgoing interface. As noted, this method is suitable for point-to-point links (like a serial interface) but will not work on multi-access media like Ethernet for IPv6. The router will accept the command but will not forward packets.
  ipv6 route 2001:DB8:0:3::/64 Serial0/0/0

• Fully Specified Static Route: You specify both the outgoing interface and the next-hop address. This is the most explicit and often recommended method, as it avoids the recursive lookup and works reliably on all interface types, including Ethernet.
  ipv6 route 2001:DB8:0:3::/64 GigabitEthernet0/0 2001:DB8:0:12::2

A special consideration arises when using a link-local address (LLA) as the next hop. Because LLAs are only unique on their specific link, you must use a fully specified route that includes the outgoing interface. The router cannot determine which interface to use from the LLA alone.

The following reading provides a helpful table summarizing these methods and shows detailed configuration examples.

Configuration and Verification in Practice

Now let's apply these concepts to configure the three main categories of static routes: network, default, and host. The following image provides a complete topology that we can refer to.

1. Network Route

A network route directs traffic destined for an entire subnet (e.g., a /64 prefix). In the topology above, to enable communication between the loopback networks on BR1 and BR2, the HQ router needs routes to both.

On HQ, to reach BR2's loopback network 2001:AA:2:2::/64, you could configure a fully specified route pointing to BR2's GUA on the connecting link:

HQ(config)# ipv6 route 2001:AA:2:2::/64 Ethernet0/1 2001:AA:0:2::2

Alternatively, using BR2's link-local address (fe80::2) as the next hop is also very common:

HQ(config)# ipv6 route 2001:AA:2:2::/64 Ethernet0/1 fe80::2

2. Default Route

A default route (::/0) is a catch-all that matches any destination not explicitly found in the routing table. It's often used on edge or branch routers to forward all outbound traffic to a central location or an ISP.

The following diagram illustrates a classic scenario where a Branch router uses a default route to send all traffic to the HQ router, which handles connectivity to the broader internet.

To configure a default route on the Branch router pointing to HQ's address 2001:DB8:D1A5:C900::2, the command would be:

Branch(config)# ipv6 route ::/0 2001:DB8:D1A5:C900::2

3. Host Route

A host route is a route to a single IPv6 address, specified with a /128 prefix length. This is useful for directing traffic to a specific server or critical device with maximum precision.

For example, to create a route on R1 specifically to the host 2001:DB8:2:2::2, you would use:

R1(config)# ipv6 route 2001:DB8:2:2::2/128 2001:DB8:12:12::2

The following article walks through clear, step-by-step examples for configuring each of these three route types.

Verification

Once configured, verification is a two-step process:

1. Check the routing table: Use show ipv6 route static or show ipv6 route and look for an entry beginning with S. This confirms the route is installed. The entry will show the destination prefix, administrative distance/metric [1/0], the next hop, and sometimes the outgoing interface.

   R1# show ipv6 route
   ...
   S   2001:AA:2:2::/64 [1/0]
        via FE80::2, Ethernet0/1
   

2. Test connectivity: Use ping and traceroute with IPv6 addresses to confirm end-to-end reachability. As shown in the "IPv6 Static Routing Configuration Example" image, the traceroute 2001:AA:2:2::2 command from BR1 successfully shows the path through HQ to BR2.

A Note on Floating Static Routes

What if you have a backup path you only want to use if the primary path fails? This is achieved with a floating static route. It's a regular static route configured with a higher Administrative Distance (AD). Since routers prefer routes with the lowest AD, this backup route "floats" above the primary route and is only installed in the routing table if the primary route disappears.

You can set the AD by adding a number at the end of the command:
R1(config)# ipv6 route 2001:DB8:0:3::/64 2001:DB8:0:13::3 210

Here, the AD of 210 makes this route less preferred than a route learned via a dynamic protocol like OSPF (AD 110) or another static route with the default AD of 1.

Conclusion

In this lesson, you have moved from automated configuration to manual, explicit path control in IPv6. By mastering static routing, you gain the ability to precisely dictate how traffic traverses your network, a foundational skill for any network engineer.

Key Takeaways:

• IPv6 static routing is configured with the ipv6 route command, which requires ipv6 unicast-routing to be enabled globally.
• You can create network routes (/64), default routes (::/0), and host routes (/128).
• Routes can be specified in three ways: recursive (next-hop GUA only), directly attached (interface only, not for Ethernet), or fully specified (interface and next-hop).
• When using a link-local address (LLA) as the next hop, you must also specify the outgoing interface.
• Verification involves show ipv6 route to check the table and ping/traceroute to test connectivity.
• A floating static route uses a higher administrative distance to create a backup path.

Our next lesson will build on this foundation by exploring how networks can learn routes automatically. We will configure OSPFv3, the primary link-state dynamic routing protocol used for IPv6, allowing routers to discover topology and calculate the best paths without manual intervention.