Saturday, April 18, 2015

OSPFv3 Gets Family

It's been a while since I touched Cisco CLI during Non Office Hrs. There are lots of things keeping me busy enough these days like I have been doing a Proxy relocation to DC project which means tons of stuff to deal with as DC is a fairly complex structure with lots of moving pieces like Load Balancer ( SLB, GSLB, LLB), Firewalls and above that this particular DC runs all Juniper Devices for Routing , Switching & Security stuff.

On the flip side I am thinking to seriously start working on CCDE from Mid May 2015 onwards with first lab attempt probably in Feb or May 2016. Though initially CCIE Wireless was on Radar for this and coming year but as Cisco has just announced new blueprint , the idea went on to backseat for a while now. Voice could have been interesting also but similarly CCNA and CCNP Collab tracks are going to replace existing NA and NP Voice track soon and moreover I haven't been doing much around Voice at work as well so should consider it some time next year.

Now back on to idea of today's post about OSPF Address Family Structure. Well it's been a while since Network Industry was talking about one of advantage of IS-IS over OSPF which is IS-IS supports IPv6 natively. For IS-IS it was just a matter of adding new TLV (Type Length Value) to existing IS-IS packet ( TLV 232 & 236 ? I guess). Where as with OSPF it was a different story. They actually had to write a new routing protocol right from scratch now known as OSPFv3. Which introduced another problem from network design and management standpoint that if we just want to run OSPF as choice of routing protocol for both IPv4 & IPv6 on network as administrator, we got to run two separate routing protocol instances as OSPFv2 for IPv4 and OSPFv3 for IPv6. Which means two separate routing topologies.

Now with OSPFv3 Address family (AF) structure support we get rid of this problem of running two separate routing instances somewhat. Why "somewhat" and not "completely" ?

Well while this AF structure solves the multiple instances requirement problem, it has it's own limitations like:

> Specific IOS version like 15.x required, which may or may not be supported across all existing routers & switches serving as Distribution block

> The AFv4 requires IPv6 Link Local address on all IPv4 interfaces in order to function, otherwise it doesn't allow you to bind OSPFv3 AFv4 instance on interface. The Link local addresses are used as source address of packet over interfaces connecting OSPF enabled devices

> The device with capability of AFv4 still couldn't talk to traditional OSPFv2 Device since there is a Address Family bit carried inside new Hello packets which traditional OSPFv2 device don't understand

Which means the deployment is more likely to be successful only if it's a Green Field deployment.

Here is a quick lab with quick results :)

Further Readings:

Deepak Arora

1 comment:

Shreeram Pardhy said...

Hi Deepak,

I have always been thinking why we would want the link LSA when the prefix LSAs are doing a similar job. Both of them are advertising the prefixes that are configured on a link. The only difference being the link lsa is also advertising the link local address configured on the link from where the advertisements are being sent out.however i cant really reason out why we need to advertise the link local address in a LSA when the boxes are already using that address as source ip in their hello packets. All teh devices connected on same link ( or for that matter same layer 2 network ) would come to know the other routers link lsa in two ways.
1. Routers generarting RAs contain the link LSA
2. OSPF hello packets are already using source ip as link lsa.

Would like to know your thoughts about the link LSA and why it is needed :)