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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