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Are there any practical speed/latency gains from using IPv6, or is it just to make room for more IPs?

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there's other advantages though, like rendering NAT practically obsolete, and allowing pretty much anyone to have a static ip address – Journeyman Geek Aug 28 '10 at 1:36
Well I dunno if NAT is "obsolete", maybe unnecessary, but I could see benefits in having your network secured off from the rest of the world save for some basic entry points. Also I think most anyone who wants a static IP currently can have one, ISPs just find it easier to assign them dynamically. You still end up with the same amount of IPs given out. – Bob Aug 28 '10 at 17:49
@Bob Any real security (obscurity does not count) you got from NAT can be done in IPv6 with a stateful firewall. – Azendale Jan 1 '12 at 4:08
That argument sounds a lot like "If you have a firewall you don't need a router to protect you online"; in theory it sounds good, but in practice... Well, I imagine we'll all find out soon ; ). – Bob Jan 2 '12 at 3:44
@Azendale: Obscurity is a real obstacle, just like how a door lock is a real obstacle. Neither is good enough to prevent against anyone who seriously wants to break in, but they both help making what's already there more secure. – Mehrdad Apr 4 '13 at 8:07
up vote 24 down vote accepted

Practical impact? Not really. The effect is pretty small. Where you might run into it is in high latency links (think satellite) where the MTU (maximum transfer unit) is small, which magnifies the impact of the larger overhead IPv6 requires. That's an edge case. The other area where you'll see impacts is when you're doing 6 to 4 translations in the network path, as that always takes some time. But if you had a pure v6 path to that other v6 host such latencies won't be an issue.

In these days of TCP Offload Engines coming built in to more and more network stacks the impact is even less likely to be noticed. If any. In fact, it may even be faster in those cases.

Why is that larger header not as much of a factor as you think? That's because the designers of v6 took some of the lessons of v4 and built things better. Most importantly for cross-internet communications the address fields are handled much more efficiently in routers than in v4, which improves speed of v6 packets through routers as compared to their v4 cousins.

When it comes to same subnet communications where router tables aren't a concern, each packet requires less raw computation. There is one less checksum to validate (Ethernet checksum, no IP checksum for v6, but TCP/UDP checksum is still required) which saves small amounts of time. And on special networks, the ability to have VERY large packets can further save processing.

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Maybe the word latency confuses what I meant, I was just wondering if using ipv6-ipv6 would be faster than ipv4-ipv4 in a noticeable way. Great info though, thanks! – Bob Aug 27 '10 at 23:45

You might see performance improvements with IPv6 if there is a slow router between you and your destination which would have fragmented IPv4 packets along that path. With IPv6, routers will no longer fragment packets for you. (the responsibility has been delegated to end nodes.)

Of course, this is an edge case. There is no reason to believe IPv6 will perform better than IPv4 in the general case.

Also, router vendors may also have optimized their IPv4 data paths more than their IPv6 data paths. So until IPv6 routers have equivalent optimizations, IPv6 may be slower. (For example, some routers may do IPv4 routing in hardware, but IPv6 in software. High-speed performance tests would have to be done to identify this.)

So you have to weigh the chances that there is a router that isn't optimized for IPv6 between you and your destination with the chances that there is a router doing fragmentation of IPv4 packets between you and your destination. ;-)

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I've been running dual stack IPv6/IPv4 for a while now, and I'm a huge fan.

I can tell you that most of the time the performance and latency are about the same. But on occasion, IPv6 will make your jaw drop.

Consider my ping times to Google:

On IPv4:

rtt min/avg/max/mdev = 35.557/38.225/43.909/3.146 ms

On IPv6:

rtt min/avg/max/mdev = 39.202/40.923/43.105/1.501 ms

Nearly identical. That's what I see most of the time. But every so often, such as when I'm accessing one of my own servers, which is also on IPv6...

On IPv4:

rtt min/avg/max/mdev = 123.510/124.249/125.997/0.909 ms

On IPv6:

rtt min/avg/max/mdev = 87.140/88.600/90.727/1.255 ms

The big difference here, of course, is my ISP's less than optimal IPv4 routing for this route and much better IPv6 routing. (IPv4 goes Boston-Chicago-Denver-Seattle-LA-Phoenix. WTF? IPv6 goes Boston-DC-Atlanta-Dallas-Phoenix.) I suspect there are lots more of these out in the wild.

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In my experience of comparing traceroute6 vs. traceroute, IPv6 is faster, even through a tunnel broker. This is probably because IPv6 generally requires fewer hops to get from point A to B.

Here's a third-party source backing up my observation:

Accessing sites and content over the Internet is usually faster with IPv6 than with IPv4 because with the new protocol it requires fewer "hops" between network nodes
Here is a little experiment I ran using traceroute/traceroute6, ping/ping6, and my Hurricane ( tunnel, gathering the sites with both IPv6 and IPv6 capabilities from
SITE                    IPv4 hops       IPv6 hops       IPv4 ping (min/avg/max/mdev ms) IPv6 ping (min/avg/max/mdev ms)            14              8               67.253/72.499/106.113/11.265    55.031/58.340/74.078/5.426                13              10              45.450/53.924/98.121/15.158     60.002/82.812/196.221/41.448            >13             10              -                               92.043/92.840/94.055/0.680              11              7               59.059/66.432/95.884/10.134     52.423/73.042/135.103/30.874             >11             6               33.178/97.481/536.719/148.432   45.562/47.133/48.390/0.805    9               9               85.383/286.941/527.103/155.351  76.788/169.458/516.502/147.166           10              5               34.021/39.507/70.518/10.384     33.009/41.441/70.052/13.069    15              13              86.739/93.772/120.192/10.195    91.341/93.146/97.153/2.006       >14             8               86.186/401.432/1629.098/502.373 92.437/481.830/727.557/241.649    12              6               35.443/40.502/70.426/10.056     33.953/41.144/85.444/14.862        >9              >4              39.504/46.119/73.483/10.290     32.559/63.532/222.700/62.022
So, indeed, IPv6 uses fewer hops and is overall no worse, if not slightly better, performance-wise than IPv4, even though my IPv6 is going through a tunnel.

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No, there would be no speed gains to speak of, although routing tables are certainly made simpler.

To say that IPv6 "just" makes more room on the net is like saying the Milky Way Galaxy "just" makes more room for dust grains. IPv6 essentially makes it so that it's literally impossible to run out of IP addresses. Even if we were to carpet the entire surface of the earth with CPUs, each with its own IP address, we'd still come nowhere near IP exhaustion. The number of IP addresses in v6 is totally incomprehensible.

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Can I quote you on that? I'd like to bring it up when every toaster, refrigerator, oven, microwave, pencil sharpener, car, tractor, house, and human being has their own IP and we're looking to expand via IPv8. :P – Aeo Feb 10 '11 at 18:54
You sure can. If you wanted to, you could assign 2000 IPv6 addresses to every square meter of the disc of our galaxy. There are 2^128 possible IP addresses in this scheme, or over 3x10^38. This is more than a billion billion times the total number of IPv4 addresses. You could even assign IPs to every single component of every single household item ever made in the entire history of humanity, until the end of humanity itself. – Ernie Dunbar Feb 10 '11 at 20:25
But it is essentially just to add more IP's? ; ) That is a lot more than I imagined v6 adding, and I thought it added quite a bit. Still, the adage is every time you give someone a mile of rope they realize they needed ten, with double the weight capacity. IP's on a molecular level with nano-tech could eat them up, who knows. (Then again I suppose you could nat that to your local organism IP) – Bob Feb 11 '11 at 13:50
Oh don't worry. Before the end of this year, the whole world will see the value of IPv6. In spades. And on the front page of every newspaper. – Ernie Dunbar Feb 11 '11 at 16:44
Bob: There are a number of other advantages to IPv6. Some of them have been backported to IPv4, but often not quite as effective. The main driving force currently is v4 address exhaustion though. Check wikipedia: – Martijn Heemels Jul 14 '11 at 9:42

No ip checksum in IP v6 pockets as in IPv4 pockets in intermediate nodes etc . And also the fragmentation of IP v4 pockets takes place and reassembled at routers in IPv4 and the same is not there in v6 . This indicates less no of computations the pockets undergo in v6 in the transmission . As such all these will add up to its own fast processing / routing in built functions of Ipv6 o make it faster . This only I summed and indicated. Pl some one can improvise this . As regards to less hops for Ipv6 indicated above wh means that IPv6 pockets travel in different route in the test performed Is that correct or any other addl attributes to this

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Please use correct spelling and grammar on this site, stuff like this makes my eyes want to skip over it. – David Nov 15 '13 at 14:16

Since there is no fragmentation and checksums etc , forwarding of packets is fast and thereby speed also must be better than IPV4

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Can you elaborate on this? This needs more specifics to be a useful answer. – Dave M Oct 31 '13 at 17:02
Actually, as this is a sum up of the accepted answer, it wouldn't qualify as a good answer by itself, unless it states a different point of view. – Doktoro Reichard Oct 31 '13 at 17:03

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