mike-jumper commented on code in PR #268:
URL: https://github.com/apache/guacamole-manual/pull/268#discussion_r1970690596
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src/guacamole-docker.md:
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@@ -176,6 +176,31 @@ detail in the sections below. If the required
configuration options for at
least one authentication mechanism are not provided, the Guacamole image will
not be able to start up, and you will see an error.
+(guacamole-docker-ipv6)=
+
+### Configure Guacamole to prefer IPv6 for outbound connections
+
+By default, Guacamole will use IPv4 for all outbound connections, where an
+A record is present in DNS. IPv6 will be used only if there are only AAAA
+records in DNS, or if an IPv6 address is hard-coded.
+
+Additionally, Guacamole will only attempt to make one connection to a single
+IP address, so if the IPv4 connection fails, it will not fall back to IPv6.
+This can be problematic for IPv6-only deployments, where such connections may
+fail with a "Network is unreachable" error.
+
+To override this, set the `JAVA_OPTS` environment variable to
+`-Djava.net.preferIPv6Addresses=true`.
Review Comment:
I don't think this is entirely correct:
* The JVM defaults to preferring IPv4. That's not to say this isn't worth
documenting, but it's not something specific to the Guacamole webapp.
* As written, it sounds like connections to other machines (ie: remote
desktops) will fail for IPv6, but this is not the case. The JVM configuration
option in question controls only whether IPv6 is used by the JVM, which would
affect only the connection to guacd itself and external auth systems
(databases, LDAP, etc.).
This is eventually clarified later, but I think we can avoid the confusion
earlier by specifically noting what this affects. Users would need to set this
option only in the event that they need IPv6 to communicate with their own
guacd service, their own database, or other authentication backends.
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