• 07/07/2014
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Understanding IPv6: The Journey Begins

Why is IPv6 so difficult to understand? Denise Fishburne explains how she began unraveling this complex topic.

IPv6 and I met back in the early 2000s. I really didn't see the big deal or know what all the RFCs were about. This stuff was easy. Of course, at the time, my thoughts were barely even scratching at the surface, and I still believed IPv6 was just IPv4 with 128 bits. I was in what I now refer to as the "Checklist IPv6" phase.

"Checklist IPv6" was actually a great place for me to start. I had to remember only a few things while I was configuring the routers. Then I could kick back and let the magic of routing protocols work. Voila, IPv6 addresses would show up in the routing table of some other router in the lab. Ping to confirm, and I was done.

IPv6 "I know nothing" phase
The quote "The more you know, the more you realize how much you don't know. The less you know, the more you think you know," is attributed to David T. Freeman. I discovered the truth of this as I began digging deeper. The trigger to this phase was when I realized that IPv6 was clearly not IPv4 with 128 bits. When did that happen? When I read that there was no broadcast in IPv6.

That started an avalanche of questions, including:

  • Why the heck did they get rid of broadcast?
  • If there is no broadcast, how does one resolve MAC addresses?
  • What is this weird link-local address thing?
  • What do you mean you can just randomly generate your own link-local address? And why not?
  • Solicited-node multicast? Really?
  • This SLAAC thing has two different flavors?

I was honestly struggling with the impossibility of memorizing all these varying attributes. It all culminated in one question that eventually formed in my mind. The question went something like "Seriously? Why couldn't we have just stayed with IPv4 and increased it to 128 bits?"

The reverse-engineering phase
We all have strengths and weaknesses. One of my weaknesses is the ability to memorize a list of facts. I'm much better if I can see a flow, an equation, or a reason in my mind. So I had to spend some time trying to reverse-engineer the "why" of IPv6.

It was the year 1993. BOOTP required much manual intervention, and there was concern that IPv4 addresses would run out. In October of that year, RFC 1531 was published, defining DHCP as an extension to BOOTP. A couple of months later, RFC 1550 solicited for white papers on "IP Next Generation" (IPng). RFC 1550 helped take me back in time to the issues that were at the forefront of people's minds and what the IPng protocol would need to address. I specifically liked one quote in section 5: "Any or all of these issues may be addressed, as well as any other topic that the author feels is germane."

That one sentence essentially gave me permission to imagine all the things people might have thought were "germane" to the next generation of IP. I came up with the following potential discussions that could have happened between 1993 and 1996, when RFC 1970 was produced, defining IPv6's Neighbor Discovery protocol.

  • Broadcast: Why broadcast to every device on the segment? Why bother every device on the segment to process a broadcast? Can't we do MAC resolution a different way?
  • IPng addressing on local links: Why use up precious IPng addresses supporting routing protocols on a local segment just for the purpose of routers talking to each other? They are just communicating on that local segment.
  • BOOTP manual intervention: Isn't there a better way for devices to get IPng addresses? Or to get the options and information they need? Or to find out who their default gateway should be?

Did all these questions actually come up? I have no clue. But thinking about them has helped me reverse engineer some potential "whys" of much that has confused me about IPv6.

Sharing my journey
As I mentioned earlier, I don't really learn well by just memorization. I have to see a flow, a reason, or an equation and then play with it. At first, in the darkness, there is really just darkness. Then there's an occasional "hmmmm." Then there's a flicker of a potential light of understanding that might -- just might -- be around the next bend. You're rewarded with an "a-ha" moment that lasts for only a moment, until that "a-ha" brings up still more questions.

But for right now, I'd like to share my fun in the lab and what I have learned with you in this series. Next time, we'll talk about and look at sniffer traces and debugs.


reverse engineering

Thanks for sharing your IPv6 experience Denise. Your reverse engineering process is intriguing. Looking forward to your next column!

Re: reverse engineering

Thanks.  :)  Definitely having fun writing it.

Re: reverse engineering

"I still believed IPv6 was just IPv4 with 128 bits."

I think that the IPv6 is most commonly used as if it were IPv4 because there is often a translation happening where the IPv6 packet is encapsulated within IPv4.

Confused about Broadcast Point

I think I got a bit lost with the use of broadcast in this article.  Near the beginning, in the check list it says "Why the heck did they get rid of broadcast?".  Later in the article it says "Why broadcast to every device on the segment?"

My understanding of why broadcasting was changed is that you could eventually eliminate the need for centralized DNS servers.  You could also eliminate the need for DHCP to assign unique addresses because nodes could query peers in the process of looking for an un-used address.  That said, I might not be using the same definition of broadcast as was used in this article.

Re: Confused about Broadcast Point

When I realized that IPv6 had no concept of broadcast, that, admittedly in the beginning, really tripped me up.  Why oh why oh why did they do that?

Then I started looking backwards into the world in which IPv6 was originally born... it occurred to me that maybe someone said "why broadcast to every device out on a segment? can't we think of a better way of doing this?".    Imagining the potential conversations and questions presented back in the early 1990s when IPv6 was born has decidedly help me potentially grasp some of the "whys".

Broadcast as in truly all 1s on the destination mac address like one would do for an ARP. 


IPv6 Controversy

An interesting topic that does not often get much attention is how IPv6 might affect people's privacy. 

Once IPv6 becomes the norm, ISPs will be able to assign dedicated IP addresses.  There are some potential benefits to static IPs, but there are also some potential issues of privacy if that IP becomes a unique identifier for your specific computer.

Re: IPv6 Controversy

Honestly I had not thought about that. Yet another thing to learn and wonder about.  :)  I'll have to ask my IPv6 friends that are decidedly at that "IPv6 subject matter expert level".  

Re: IPv6 Controversy

@AbeG: Conversely, with the necessary IP-sharing that must come without quick-enough IPv6 deployment, an innocent may get accused of a computer crime perpetrated by a do-badder with a device sharing the same IP.

Re: IPv6 Controversy

@Joe.  I've always assumed that for crimes where there is a financial penalty like media piracy, the law simply holds the account owner responsible when it comes to residential internet.  Perhaps similar to how a vehicle owner might be held responsible for whatever is found in the vehicle.

I think that when it comes to more serious penalties, the burden of proof is very high.  It seems that someone would have to show which MAC address was transmitting the data packets, which I don't think the ISP would know unless they own the router that you use.  Then there's the issue of MAC address spoofing and the reality that malware can route malicious traffic through your PC.

Re: IPv6 Controversy

@AbeG: It depends whether it's a civil issue or a criminal issue.  Criminal prosecutions -- even ones punishable by but a fine -- are still subject to the "beyond all reasonable doubt" burden of proof in the United States.  In most civil cases, however, the plaintiff's burden of proof tends to be "by a preponderance of the evidence" (that is, a greater than 50% chance).

Re: IPv6 Controversy

I would imagine this issue gets more attention as IPv6 becomes more widespread. The privacy concern seems valid, but some argue that IPv6 has features that protect privacy.

Re: IPv6 Controversy

Thanks for the link, that was an interesting read.

"In any case, the best way to track someone's behavior is not by address anyway, because people change networks too often.  Smartphones and tablets move back and forth between mobile networks and Wi-Fi networks throughout the day."

When it comes to private WiFi networks that we use regularly, I think it's common to get assigned the same IP as before.  Having multiple IP address seems like it would create routing problems. 

Has anyone ever had their laptop connected via ethernet and wifi at the same time?  I have.  I've also experimented with using one connection for incoming traffic and the other for outgoing traffic.  Both configurations have their share of issues.


Re: IPv6 Controversy

You are right on routing part, another is that some existing networking protocols, like WCCP, may be designed to operate in IPv4 only and even when both the routers and web caches are IPv6 capable, some traffic may not be redirected due to the WCCP limitation. These types of problems are much more difficult during migration towards IPv6.

Re: IPv6 Controversy

@Marcia: I think it's a moot point, because we were supposed to have FULL IPv6 deployment by about--what--six years ago, give or take?

Instead, the issue inspired IPv4 address hoarding -- and the movement towards IPv6 has been paid but lip service all of this time.

My bet: It doesn't even get done this decade.

IPv6 Journey

Please hurry up.


Re: IPv6 Journey

:)  I think we are looking at a post every 2 weeks for this.  I already have all the "raw" material - the sniffer traces, debugs, configs, what order to show, etc. Now to piece each one together. 2nd one almost finished.   

Very glad you like them. They are very fun to do.

Good Article

This is a very good article that certainly brings to light the IPv6 issues that are coming (or are already here).  Makes me continue wonder when IPv4 will take a back seat as I've been believing it would for several years.  Thank you for the great article Denise.

Re: Good Article

I have about 3-4 more coming. They will be sniffer traces, 2 routers, and some debugs.  :) As you can see, I'm a "lab rat".  Course, the nickname is "Fish" so not sure how that works out. 

Understanding IPv6: The Journey Begins


Nice post,

iam looking for more topics on practical implementation of IPv6 in Networks & challenges on the IPv6 migration in Enterprise.

Re: Understanding IPv6: The Journey Begins

Thanks for tossing those ideas in. Added to the list. Think I have a few more "fundamentals" and understanding blogs to write 1st.  But added your stuff to the list.