My studying for the CCIE v4 Written Exam has been going well. Each day I’ve been focusing on one of the major CCIE topics after first doing a quick review of previous study items. The last few days before the exam will be a constant cram of all of the material, with a bit of emphasis on my weak points (my nemesis QoS especially).
I’ve also been making sure I have a thorough understanding of the new technology topics as I’m sure they’ll be featured on the exam. Today I’ve been really looking at the IPv6 routing protocols OSPFv3 and EIGRPv6. On the surface, these two topics have much in common with their IPv4 counterparts. But as they say, the devil is in the details. And do I hate that devil.
One of the first things you’ll notice when you start to dive into these two protocols are the similarities in the way Cisco has implemented them. Both protocols now are primarily configured with interface commands, rather then the IPv4 router-mode commands. Router ID’s are now required for not only OSPF but EIGRPv6 as well (the EIGRPv6 process won’t even start before you configure one). Both protocols also have a reliance on IPv6 link-local addresses as their source/next hop address for IGP communications.
OSPFv3, while very similar to OSPFv2, still has some significant differences. The one that I think everyone keys on (for good reason) is the two new LSA additions – the Link LSA and the Intra-Area Prfix LSA.
The Link LSA, or type 8 LSA, is used only between directly connected neighbors. It allows each neighbor to describe which prefixes it is associating with the link. The Intra-Area Prefix LSA, or type 9 LSA, is a bit more complicated. In OSPFv3, Router and Network LSAs no longer carry prefix information – they are simply the carriers of topology information needed for OSPF to build SPF tables. The carrying of the prefix info in OSPF3 falls instead to the Intra-Area Prefix LSA, which will now be flooded throughout an area when prefix information changes. The beauty of this design is that a change in prefix info will no longer trigger a new SPF calculation – the OSPF routers simply associate the prefix info with the originating router. Cutting back on resource utilization is always a good thing 
.
There are a few other details you should know about OSPFv3. Authentication is no longer built right in to the protocol; OSPFv3 relies on IPSEC instead to deliver packets securely. Also remember that when you configure OSPFv3 on an interface it will automatically include any and all IPv6 addresses you have configured on that interface.
I think that EIGRPv6 is even more similar to its IPv4 “little brother” then OSPFv3 is. EIGRP concepts like the various timers, metrics, and variance ideas are the same – but you will need to get used to some different configuration command syntax. Auto-summary is now gone (Yay!); and don’t try to use a route-map with the distribute-list command either, because you won’t be able to.
One absolute must with EIGRPv6 is to remember to turn the damn thing on. When EIGRPv6 is first configured on an interface, the IOS will create an EIGRPv6 process, but it will be in a shutdown state. You’ll need to go into router config mode and enter a good ol’ no shut command to start ‘er up.
That’s about all I’ve discovered for now, but I’m sure there’ll be more surprises once I jump in and start playing with these technologies. Rest assured that everything I discover will be dumped into the CCIE Study Wiki so we all can benefit from it.
Thanks for reading!
Jason