Also Geoff has measured this : https://nanog.org/events/nanog-66/content/1078/
https://archive.nanog.org/sites/default/files/Huston_Is_Ipv6.pdf 10 years old now, but his conclusions then were if you could establish a connection, V4 and V6 latency was basically the same. ( Unless 6 to 4 was involved. ) On Tue, Dec 2, 2025 at 12:29 PM Lee Howard via NANOG <[email protected]> wrote: > 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 > >> > >> Send spam to [email protected] > > _______________________________________________ > > NANOG mailing list > > > https://lists.nanog.org/archives/list/[email protected]/message/EBHOWLWPDOYOV2ATJPYBAA2CLI6SMIEE/ > _______________________________________________ > NANOG mailing list > > https://lists.nanog.org/archives/list/[email protected]/message/IL5AHCAXCZRJACSQMCFETQEY4GDVX57L/ _______________________________________________ NANOG mailing list https://lists.nanog.org/archives/list/[email protected]/message/DEC4SWYZBS2JQOUKP3OVCVCSTXVCGZXW/
