-----Original Message-----
From: Lee Howard via NANOG <[email protected]>
Sent: Tuesday, December 2, 2025 20:28
To: [email protected]
Cc: Lee Howard <[email protected]>
Subject: Re: IPv6 Performance (was Re: IPv4 Pricing)
Before you call people silly, you might want to collect some data.
You would think IPv6 headers would add processing time, but that turns out
not to be the case. Yes, they may sometimes be routed along different paths,
but I have seen IPv6 have fewer hops and lower latency as often as I've seen
IPv4 be faster. When I was at a large network, I published these results,
measuring from many points in the network to many common destinations,
and there was no predictable difference.
This is true for CGN, firewall, load balancer, router, translator, or any other
hardware. The *only* exception is some limited release devices that kicked
IPv6 forwarding to the software plane; I would argue that that is not IPv6
support. If anyone else has contrary experience or data, please share. To be
fair, such devices also do not add measurable latency in performing NAT44.
Many networks have reported that IPv6 has lower latency, in fact.[1] In North
America, IPv6 has a 2ms advantage over IPv4.[2]
This is *as measured* not based on theory.
My hypothesis, supported but unproven, is that when a device uses or prefers
IPv6 (such as on an IPv6-only network with translation) and tries to reach an
IPv4 destination, the device uses software CLAT to convert IPv4 to IPv6 in the
device before forwarding. This would be the case, e.g., for an Android device
on an IPv6-only network like T-Mobile, maybe Charter. [3] I haven't seen the
new Windows CLAT, but it wouldn't be surprising.
It is fair to say that in general or overall, IPv6 has a slight performance
advantage over IPv6. That may not hold true for all permutations of endpoints
or devices, so your individual experience may vary.
Lee
[1] e.g.,
https://www.internetsociety.org/blog/2015/04/facebook-news-feeds-load-20-
40-faster-over-ipv6/
[2] https://stats.labs.apnic.net/v6perf/XQ
[3] Measurements and explanation at
https://www.arin.net/blog/2019/06/25/why-is-ipv6-faster/
On 12/2/2025 2:09 AM, Vasilenko Eduard via NANOG wrote:
Fundamentally, IPv6 should be slower because of the bigger
headers/overhead.
But it could be faster because CG-NAT detour (if CG-NAT is not on the
shortest path).
IPv4 and IPv6 could both be faster/slower because of non-congruent peering
topology.
Actually, the claim that IPv6 is faster is pretty silly.
Ed/
-----Original Message-----
From: Marco Moock via NANOG <[email protected]>
Sent: Tuesday, December 2, 2025 07:42
To: [email protected]
Cc: Marco Moock <[email protected]>
Subject: Re: IPv6 Performance (was Re: IPv4 Pricing)
On 01.12.2025 16:44 Bryan Fields via NANOG <[email protected]>
wrote:
At least once or twice a month I'm downloading something and will find
the IPv4 to transfer significantly faster. Case in point, I
downloaded the proxmox iso yesterday to a colo server with 50g
uplinks. It loafed at 2.4 mbytes/s using default wget, which of
course preferred ipv6. Adding -4 to wget made that shoot up to 80
mbytes/s.
Have you checked packet loss and latency?
Maybe that is caused by different routes due to peering.
--
kind regards
Marco
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