Understanding IPv6

We’re going to spend some time teaching you a number of incredibly wonderful things about IPv6, such as why network administrators need to get their duffs up and implement it, bullet points to persuade the bosses, and, of course, how to actually use it.

Persuasive Bullet Points

IPv6 means a whole lot more than just having a large enough pool of addresses to give every grain of sand and star in the sky a pool of unique addresses to play with. It also incorporates a lot of long-needed improvements in the IP protocol:

  • No more NAT (Network Address Translation)
  • Autoconfiguration
  • No more private address collisions
  • Better multicast routing
  • The newfangled anycastrouting
  • Simpler header format
  • Simplified, more efficient routing
  • True quality of service (QoS), also called “flow labeling”
  • Built-in authentication and privacy support
  • Flexible options and extensions
  • Easier administration say good-bye to DHCP

No More Lollygagging

You’ve probably read articles that claim the cost of migrating to IPv6 is going to be huge and painful, on the scale of Y2K. I don’t think so. Naturally, anyone who is clinging to ancient routers and switches that don’t support IPv6 is going to suffer the pain of buying new hardware. By design, IPv6 and IPv4 are going to co-exist for some time, so administrators can take their time and migrate in nice, sane small steps. No doubt some will suffer headaches from having to stuff new knowledge into their heads, but trust me, it’s worth it.

Probably the biggest selling point for IPv6 is the shortage of IPv4 addresses. Here in the good old US of A, in typical overlord fashion, we possess the majority of them. While NAT and CIDR notation have extended the number of usable IPv4 addresses, NAT needs to go away forever, and the rest of the world can’t live on our scraps.

Death to NAT

I long for the day when the final stake is driven through the heart of NAT. NAT extended the useful life of IPv4, which is a good thing, but in itself is a horrid kludge that has driven far too many network administrators to drink and hair loss. Why does NAT suck? For a number of reasons. First of all it’s a big fat chokepoint on your network border, forcing every single packet that enters or leaves your network to be examined and altered.

Secondly, NAT complicates every service, requiring all sorts of corollary hacks to make things work, especially services that use multiple ports. Everyone who survived the days of trying to make things like IRC, FTP and NFS work through NAT firewalls deserve medals. Most services have been around long enough to accumulate enough kludge work to deal with NAT, but new services still have to go through the pain cycle. Like the SIP (Session Initiation) protocol for voice-over-IP (VoIP), Bit Torrent and other peer protocols, plus anything that you want to run on multiple machines behind the same NAT address.

Colliding Private Addresses & Simplified Routing

All those lovely, unique IPv6 addresses instantly cure a large IPv4 problem: private address collision. This happens when you have to integrate subnets that use the same IPv4 private address space.

The IPv6 header is completely re-designed. Required components are moved to the front of the header. Optional components are moved to an extension header; if there aren’t any optional components, the extension headers are omitted and the packet size is reduced.

But that’s not all. The IPv6 protocol is ingeniously designed so that our hardworking spam-burdened Internet backbone routers will have much smaller routing tables than they do now. No longer will they need to know every possible route, which is why those big backbone routers are the size of Ford Exorbitants. Instead of having to know every possible route, the routing tables will include routes to only those routers connected directly to them. The IPv6 protocol itself contains the remaining information a packet needs to reach its destination.

Real, Genuine QoS

QoS in IPv4 is a bit of a joke. Sure, packets can be assigned different priorities, but a lot of routers simply ignore the QoS flag, and certain networking stacks are rumored to mark all packets as highest priority, so it’s pointless to even try.

In this modern era of gigabyte and multiple-gigabyte networking speeds, voice over IP, streaming video, and other high-demand real-time services, that sort of clumsiness simply will not do. IPv6 is designed to handle these new super-high speeds, and it standardizes QoS so that all routers will handle packets correctly, even allocating bandwidth according to priority.

Easier Administration

Don’t be scared by those long hexadecimal IPv6 addresses. We’ll learn how to break them down into manageable chunks, some shortcuts to save typing, and understand what each piece means. There are two separate address spaces for private addressing called “link-local” and “site-local.” A link-local address is like a single subnet and should not be routed. Link-local addresses let you do fun easy things like:

  • Host auto configuration without DHCP, simply by querying the router
  • Neighbor discovery
  • Setting up ad-hoc LANs without a router

In other words, you can fling a gaggle of strangers together in a conference room, connect all their PCs (wireless, wired, whatever), and share files without having to wrestle with file-sharing protocols. Site-local addresses are like a typical office containing several subnets. The subnet information is in the address so they can be routed within a site. They should not be forwarded outside the site.

Key Terms To Understanding IPv6

IPng (IPv6)
Short for Internet Protocol next generation, a version of the Internet Protocol (IP) reviewed in IETF standards committees to replace IP version 4. The official name of IPng is IPv6, where the v6 stands for version 6. IPv6 is designed as an evolutionary upgrade to the Internet Protocol and will, in fact, coexist with the older IPv4 for some time. IPv6 is designed to allow the Internet to grow steadily, both in terms of the number of hosts connected and the total amount of data traffic transmitted.

Short for Network Address Translation, an Internet standard that enables a local-area network (LAN) to use one set of IP addresses for internal traffic and a second set of addresses for external traffic. A NAT box located where the LAN meets the Internet makes all necessary IP address translations.

Short for Quality of Service, a networking term that specifies a guaranteed throughput level.

Carla Schroder is managing editor of LinuxToday and LinuxPlanet, both sites are part of the Internet.com network

This article was originally published on December 01, 2006

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