On 06/02/2026 10:08, Robert Stupp wrote:
Hi all,
I wanted to test for the appetite to change the current default
behavior of the IP address lookup policy on dual-stack (IPv4+IPv6)
systems.
The default evaluated in InetAddress.initializePlatformLookupPolicy()
yields 'IPV4_FIRST' to return IPv4 addresses before IPv6 addresses
unless 'java.net.preferIPv6Addresses' is set to 'true'. I wonder
whether this could be changed to the system default, relying on what
'getaddrinfo' returns?
This would make Java compliant with RFC 6724, which (strongly)
recommends to yield IPv6 addresses first.
Naively speaking, it can be confusing if something like 'curl' or
'wget' connect via IPv6, but any Java application connects via IPv4.
Although it's a tiny code change, it would be a "big" or "surprising"
behavior change. Therefore I think, if there's appetite for such a
change, it would need to go into one of the next major releases.
WDYT?
Moving to net-dev as that is where the networking APIs are maintained.
As an initial comment, changing the JDK to prefer IPv6 addresses by
default would be a significant and observable change. TBH, I don't see
this being changed without a wide survey of configurations and a JEP
that lays out the case and implications of the change.
Is your motive for asking solely because curl/wget tools prefer IPv6?
I'm wondering if there is more to the question, maybe HTTP protocol
handler or client only using the first address?
-Alan
