CCNA Routing with IPv6

Question 1

What troubleshooting drawbacks might you find with unnumbered interfaces?

You might find that traceroute and ping don’t work.

Link-local IP addresses are non-routable. That is, they can be used to forward traffic to the next hop, but you can’t add a route to a link-local address in your routing table.

Why are they non-routable? Because they all use the same subnet, fe80::/64

So, imagine that you try to traceroute or ping to a link-local address. That will work fine for the local link, but what if you want to ping an address a few hops away? The packets simply can’t route there.

This is one reason that link-local addresses for point-to-point networks (unnumbered interface) can be easier to configure, but harder to troubleshoot.

Question 2

If you use OSPF in your environment, what settings will you need for a floating static route?

The Administrative Distance would need to be higher than OSPFs metric. This way the OSPF route will be preferred. If the OSPF route were lost for any reason, the floating static route would be there as a backup.

OSPFs default AD (on a Cisco router) is 110. So the floating static route would have to be higher than that.

I generally use 200 as a nice round value.

Question 3

What is the ff00:: /8 network in the IPv6 routing table?

ff00:: /8 is the entire multicast network.

In the routing table it has a next-hop of null0. Null0 is a special next hop that discards all packets.

This means all traffic to ff00:: /8 will be discarded unless there is more specific information (that is, a more specific route; Remember LPM?)

Question 4

What type of addresses are used as next-hops for OSPFv3?

You can find this by looking at the result of ‘show ipv6 route’

The next-hop addresses for OSPFv3 learned routes are link-local addresses

Question 5

Why are these used?

Link-local addresses are used because all OSPFv3 communication between neighbours happens on link-local addresses.