Static routing describes routes that are manually configured by an administrator. While static routing can be very useful, it can also messy if static routes if they aren’t used with care.
It’s typically thought the static routing is a good idea for small, simple networks. However, static routing can be problematic even in small networks:
- They must be planned very carefully
- Configurations need to be done with great care...every detail is done manually
- Troubleshooting static routes can be “tricky”
- All routing configurations must to be done manually. This can be time consuming and the above items need to be considered again.
- An administrator for a small network may very well be off-site when a network issue arises. They may be at a bigger site within the organization or be a consultant.
- Static routing scales terribly, and as Network professionals we always like to plan for growth.
- A single network change can require re-configuration on many routers (maybe all routers).
Advantages of Static Routing include:
- Troubleshooting - If a routing protocol, for example, isn't behaving as expected a Static Route can be injected into the routing table. Since static routes have a very low AD (0 or sometimes 1) the traffic flow would immediately take the new static route.
- Can easily be used as a Default Route
- There is no routing overhead on the router's CPU.
- There is no bandwidth used between routers to manage the routes (dynamic routing protocols need to communicate with their neighbors).
- An easy way to secure routing because only an administrator can configure/change specific routes
Pro Tip: For networks of all sizes you may want to first consider a dynamic routing protocol and then add static routes when appropriate.
Configuration and Verification
To configure Static Routing we simply use the ipv6 route command to specify the prefix and prefix length of the destination network(s) along with the next hop to that destination:
ipv6 route [ipv6-prefix/prefix-length] [next hop]
The next hop can be specified with the GUA, LLA or the egress interface.
Pro Tip: Using the GUA or LLA is preferred over the exit-interface for the next hop because CEF prevents recursive lookups (IPv6 CEF is automatically enabled when the ipv6 unicast-routing command is issued).
Caution: In IPv6, CEF is disabled by default. In IOS 15.x and later, IPv6 CEF is automatically enabled when the ipv6 unicast-routing command is issued. Prior 15.X versions may require the manual entry of the ipv6 cef command.
Before moving forward, I want to mention that Static Routing is a useful and important tool if used properly. Otherwise, it does can have significant pitfalls. This lesson further builds the foundation for understanding dynamic routing protocols described in further lessons as well as routing in general.
The goal of this lab is to enable R-1 to ping R-3's g0/0 interface by using Static Routing.
R-1#ping 2001:23::3 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 2001:23::3, timeout is 2 seconds: % No valid route for destination Success rate is 0 percent (0/1)
As expected R1 can't ping R-3 because it doesn't know how to get there.
Let's take a look at R-1's ipv6 routing table:
R-1#sh ipv6 route C 2001:12::/64 [0/0] via GigabitEthernet0/0, directly connected L 2001:12::1/128 [0/0] via GigabitEthernet0/0, receive L FF00::/8 [0/0] via Null0, receive
R-1 only knows about:
- C - The route that is directly connected
- L - Routes Local to the router
To create connectivity from R-1 to R-3 (and R-3 back to R-1) let's implement the following:
- R-1: Add a static routes to R-1 so it knows how to get to R-3.
- R-2: R-2 doesn't need a static route because it's directly connected to R-1 and R-3. Their routes will automatically be injected into the routing table.
- R-3: Let's not forget to add a route to R-3. If we don't add a route to R-3, the ping will go to R-3 but R-3 won't know how to return the ping to R-1!