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Friday, November 21, 2008
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Implementing IPv6: Transition or Implementation?

People speak almost universally about “IPv6 transition planning,” or an “IPv6 transition plan.” In reality, what most people are doing is planning for IPv6 implementation, not transition.

Transition implies that you are replacing one technology with another, whereas implementation implies that you are adding a technology to what you already have. And in most cases, that’s what you’ll be doing with IPv6: Adding it to your network, not replacing IPv4. There may be parts of your network in which you replace IPv4 with IPv6, but probably not that many in the beginning.

The implication of this—IPv4 and IPv6 coexisting in your network—is that in most cases the two must interoperate. Interoperability is the biggest challenge to introducing IPv6 into coexistence with IPv4, and I’ll be writing about that later in this series on implementation.

But one of the first elements of the implementation plan is a good inventory. I’ll write about that in the next post.

  

Network World and I are going to try something new:  A live hosted chat in which you can pose questions and I’ll do my best to answer in real time.

 

Join me for this live chat on August 1, at 2PM Eastern (18:00 GMT). No registration is required; just point your browser to:

 

www.networkworld.com/chat

 

I hope to “see” you there!

 

v6 Router Memory Requirements

Useful answer?
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Mr. Doyle,
In the course of my work, I'm constantly discussing with customers their BGP setup for their networks to neighbor with their Internet providers.
One of the most common questions is the memory required on the premise router to accept a full routing table, 2 tables, partial routes, etc.
I'm curious as to your thoughts on how these minimum memory requirements change as IPv6 is implemented. On one hand, I could see the global routing table increase in size just based on pure available v6 routes but on the other hand, with the improved subnetting, I could also see a decrease, or little to no change to the current v4 requirements.
I would appreciate your thoughts on the subject as implementation for v6 comes full ahead. Router and memory sizing will be paramount to customer applications.

Regards,
Mark Jurney

Re: v6 Router Memory Requirements

Useful answer?
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Hi Mark,

In the short run, I don't think the public IPv6 routes are going to make much difference; assuming an edge router installed today will have a service life of 3 - 5 years, if you account for the understood growth of the Internet tables during that time you should be covered for IPv6.


But in the longer term, I think IPv6 is going to have a significant impact on the growth of the Internet routing table, and not in a good way. There are two reasons, in my opinion:


(1) The multihoming practices currently used with IPv4 will almost certainly continue with IPv6. Despite years of discussion on improving multihoming practice, no one has yet to come up with a workable solution and I'm more pessimistic than I once was that anyone ever will. 


(2) The "traffic engineering" practices currently being used, advertising long IPv4 prefixes into the Internet DFZ, will continue with IPv6. This results from a combination of expediency, selfishness and laziness, but it nonetheless exists.


The most promising proposals for preventing the public IPv6 routing table from getting out of control (again, my opinion) is some form of geographic aggregation policy (a number of which have been proposed). Basically IP addresses would be allocated similarlly to the way telephone numbers have always been allocated: By country code, regional and area code, and exchange code. But there are notable political, business, and technical barriers to geographic aggregation.


More than likely, though, IPv6 will not only not reduce the size of the Internet routing table, it will cause it to explode. We can probably rely, for at least a little while longer, on the router vendors to keep up with the explosion; but eventually the laws of physics intervene and we'll be faced with finding a more efficient way to run the Internet. 


The lesson to be learned from the decade it's taken for IPv6 to get off the ground is that that next step--finding a better way to run the Internet--won't happen until folks have no choice but to make it happen. 


Good topic for a few future posts!


--Jeff

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About Jeff Doyle

Jeff Doyle is president of Jeff Doyle and Associates, an IP network consultancy. Jeff is the author of Routing TCP/IP, Volumes I (read an excerpt) and II and of OSPF and IS-IS: Choosing an IGP for Large-Scale Networks. He is a frequent speaker on IPv6, MPLS, and large-scale routing.

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The opinions expressed in this Weblog are those of the writer and may not represent the opinions of Network World.

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