Review IPv4/IPv6 installation requirements (#4213)

* Merge all IPv4/IPv6 requirements into one module
* Exclude a prereq on content from foreman-el/deb

---------

Co-authored-by: Maximilian Kolb <[email protected]>
(cherry picked from commit d7107ad)

Author: aneta-petrova

guides/common/assembly_planning-project-server-installation.adoc

@@ -14,4 +14,8 @@ endif::[]
 
 include::modules/ref_port-and-firewall-requirements.adoc[leveloffset=+1]
 
+ifeval::["{mode}" == "connected"]
+include::modules/ref_ipv6-and-ipv4-requirements.adoc[leveloffset=+1]
+endif::[]
+
 include::modules/con_aws-requirements.adoc[leveloffset=+1]

guides/common/assembly_preparing-environment-for-project-server-installation.adoc

@@ -6,14 +6,4 @@ include::modules/proc_enabling-client-connections-to-project-server.adoc[levelof
 
 include::modules/proc_verifying-dns-resolution.adoc[leveloffset=+1]
 
-ifdef::installing-satellite-server-connected[]
-include::modules/proc_requirements-for-installation-in-an-ipv4-network.adoc[leveloffset=+1]
-
-include::modules/con_preparing-your-environment-for-project-installation-in-an-ipv6-network.adoc[leveloffset=+1]
-
-include::modules/con_limitations-of-installation-in-an-ipv6-network.adoc[leveloffset=+2]
-
-include::modules/con_requirements-for-installation-in-an-ipv6-network.adoc[leveloffset=+2]
-endif::[]
-
 include::modules/proc_preparing-for-using-external-databases.adoc[leveloffset=+1]

guides/common/modules/con_limitations-of-installation-in-an-ipv6-network.adoc

@@ -0,0 +1,42 @@
+[id="ipv6-and-ipv4-requirements"]
+= IPv6 and IPv4 requirements
+
+You can install {Project} in an IPv4 network or in an IPv6 network.
+ifdef::satellite[]
+Dual-stack {Project} installations that use both IPv4 and IPv6 are not supported.
+endif::[]
+
+The following requirements apply to installations in an IPv4 network:
+
+* Ensure an IPv6 loopback is configured on the base system.
+The loopback is typically configured by default.
+Do not disable it.
+* Do not disable IPv6 in kernel by adding the `ipv6.disable=1` kernel parameter.
+
+The following requirements apply to installations in an IPv6 network:
+
+ifdef::satellite[]
+* Deploy an external HTTP proxy server that supports both IPv4 and IPv6.
+This is required because Red Hat Content Delivery Network distributes content only over IPv4 networks, therefore you must use this HTTP proxy to pull content into the {Project} on your IPv6 network.
+You must configure {Project} to use this dual-stack (supporting both IPv4 and IPv6) HTTP proxy as the default HTTP proxy.
+endif::[]
+ifndef::foreman-deb,foreman-el,satellite[]
+* If you rely on content from IPv4-only networks, use an external dual-stack HTTP proxy.
+Configure {Project} to use this dual-stack (supporting both IPv4 and IPv6) HTTP proxy as the default HTTP proxy.
+endif::[]
+* {Project} does not support configuring an HTTP proxy using a direct IPv6 address.
+Instead, configure the HTTP proxy with a FQDN that resolves to the IPv6 address.
+
+If you intend to provision hosts in an IPv6 network, the following requirements also apply:
+
+* Deploy an external DHCPv6 server and configure it manually to communicate with the network boot process and to manage IP address assignment because {Project} cannot integrate with a DHCPv6 server and manage its configuration.
+For more information about DHCPv6 server configuration, see {ProvisioningDocURL}options-in-unmanaged-dhcpv6[Options in unmanaged DHCPv6] in _{ProvisioningDocTitle}_.
+* Configure {Project} for UEFI HTTP boot provisioning.
+Although {Project} provisioning templates include IPv6 support for PXE and HTTP (iPXE) provisioning, the UEFI HTTP Boot provisioning is the only tested and certified provisioning workflow.
+For more information, see xref:common/modules/proc_configuring-for-uefi-http-boot-ipv6-provisioning.adoc#configuring-for-uefi-http-boot-provisioning-in-an-ipv6-network_{context}[].
+
+.Additional resources
+ifdef::satellite[]
+* link:https://access.redhat.com/solutions/5045841[_How do I disable the IPv6 protocol on Red Hat Satellite and/or Red Hat Capsule server?_ in Red Hat Knowledgebase]
+endif::[]
+* xref:common/modules/proc_adding-a-default-http-proxy.adoc#adding-a-default-http-proxy_{context}[]