IPv6 and OSPFv3

Like most of you out there, I think about OSPFv3 and IPv6 regularly. Looking up 'regularly' in the Philip-English Dictionary we see it defined as "the day before yesterday while I was on my way home from work". Specifically, I was thinking "Huh - I don't know much about OSPFv3, and even less about IPv6".

IPv6 as I'm sure you're aware, was first proposed several years ago to put some of our out-of-work bits back to work. We've got bits everywhere with nothing to do, and here we are using a measly 32 of them in an IPv4 address. Cranking that number up to 128-bits allows us to take some of these bits off the street and make the internet more confusing to boot. It's really win-win.

With these two thoughts in mind, I decided to set up a little IPv6/OSPFv3 lab. Grabbing a spare 6504 and a couple of 4948s I set to work.

Lesson The First: any IOS version that has "ipbase" in it's name will not work. You'll be able to put an IPv6 address on a routed interface, but the command to enable IPv6 routing device-wide is missing. Go for "ipservices".

ipv6 unicast-routing is the universal command to enable (surprise!) IPv6 unicast routing. ipv6 cef could also be enable if you want to use uRPF (Unicast Reverse Path Forwarding).

Putting an IPv6 address on an interface is as straight-forward as it is in IPv4:

IPv6Lab1(config-if)#no switchport
IPv6Lab1(config-if)#no ip address
IPv6Lab1(config-if)#ipv6 address 2001:410:0:5::1/64
IPv6Lab1(config-if)#ipv6 ospf 1 area 0

Notice that the last command explicitly places the interface into OSPF area 0. Rather than say "All interfaces in network x.x.x.x/y go into area z" it's on an interface by interface basis. Personally, I think this makes it much clearer, but if there's any confusion there's always the fall-back command:

IPv6Lab1#sh ipv ospf int b
Interface PID Area Intf ID Cost State Nbrs F/C
Gi1/47 1 0 58 1 DR 1/1
Gi1/48 1 0 56 1 BDR 1/1

The bulk of the commands related to IPv6 differ only from their IPv4 counterparts in that one uses "ipv6" instead of "ip". A major gripe I have with Cisco (other than those currently displayed at dearcisco.com) is that sh ip int b shows nothing related to IPv6. Not even an indicator that the interface HAS an IPv6 address. sh ipv int b shows this information but in a much more vertical format rendering it easy to scroll off the screen. I recommend using sh ipv int b | e do|una as it filters out all the 'down' or 'unassigned' interfaces.

Getting back to configuring IPv6 addresses, the ipv6 address <blah> command can take an additional parameter of eui-64. This seems to work the MAC address into the IPv6 address which can be a bit confusing; suddenly there are a bunch of hex characters that weren't typed in. Anyway, on with the show.

OSPFv3 has some other little quirks that are handy to know. In previous versions, there was a hierarchy that OSPF would go through to select the router ID used by the device. First, it would check for a hard-set router ID. In the absence of a hard-set RID, the highest IP address on the loopbacks would be used. If no loopbacks are set, the highest IP anywhere on the device is selected. Obviously it doesn't make sense to have an OSPF process running if there isn't a layer 3 configuration on the device. With IPv6 and OSPFv3 one might think that the same logic would apply. It does. Identically. IPv6 addresses are not used for RIDs (possibly for sanity reasons) in OSPFv3. If no hard-set RID or IPv4 address is configured anywhere on the device OSPF will simply refuse to start. The day will come (if it hasn't already) when someone new to a configuration will remove the "pointless" IPv4 loopback on a device. It won't be a problem at first, but when either the chassis or the OSPF process reloads OSPF won't come back up. Brace for impact.

The moral of the story is the the output of sh ipv ospf nei will look shockingly similar to that of IPv4 and earlier versions of OSPF:

IPv6Lab1#sh ipv o n

Neighbor ID Pri State Dead Time Interface ID Interface
10.0.0.4 1 FULL/BDR 00:00:36 7 GigabitEthernet1/47
10.0.0.3 1 FULL/DR 00:00:35 54 GigabitEthernet1/48

While I won't bother repeating the commands of adding an IP address to an interface and adding an interface to an OSPF area, below are the end results of my fiddling. The topology is three devices arranged in a triangle, all IPed interfaces in area 0.

IPv6Lab1#sh ipv route
IPv6 Routing Table - Default - 8 entries
Codes: C - Connected, L - Local, S - Static, U - Per-user Static route
B - BGP, R - RIP, I1 - ISIS L1, I2 - ISIS L2
IA - ISIS interarea, IS - ISIS summary, D - EIGRP, EX - EIGRP external
O - OSPF Intra, OI - OSPF Inter, OE1 - OSPF ext 1, OE2 - OSPF ext 2
ON1 - OSPF NSSA ext 1, ON2 - OSPF NSSA ext 2
C 2001:410:0:1::/64 [0/0]
via GigabitEthernet1/48, directly connected
L 2001:410:0:1::1/128 [0/0]
via GigabitEthernet1/48, receive
LC 2001:410:0:2::2/128 [0/0]
via Loopback0, receive
OE1 2001:410:0:3::2/128 [110/21]
via FE80::8A43:E1FF:FE08:7C3F, GigabitEthernet1/48
C 2001:410:0:5::/64 [0/0]
via GigabitEthernet1/47, directly connected
L 2001:410:0:5::1/128 [0/0]
via GigabitEthernet1/47, receive
O 2001:410:0:6::/64 [110/2]
via FE80::226:CBFF:FE30:8980, GigabitEthernet1/47
via FE80::8A43:E1FF:FE08:7C3F, GigabitEthernet1/48
L FF00::/8 [0/0]
via Null0, receive

As mentioned in other attempts at tutorials, I am by no means an expert. According to Cisco, I'm merely an "associate". No guarantees are made as to the accuracy of this information. I may be wrong - in fact, I probably am. Consult a physician before changing your dose.