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Selecting the network for replication

In an HCP system that uses virtual networking, you can define multiple networks and then select the networks to use for various purposes, including replication. The network you select for replication on a given system is used for both incoming and outgoing replication traffic.

Networking infrastructure

Different HCP systems can use different networks for the purpose of replication. When you select a replication network for a given system, you need to ensure that your networking infrastructure is configured to allow communications to be routed between that system and all other systems with which that system participates in a replication link.

IP mode

The two systems involved in a replication link must be able to use the same IP mode to communicate with each other. That is, either both networks must be configured with IPv4 addresses, or both networks must be configured with IPv6 addresses.

One or both of the networks involved can have both IPv4 and IPv6 addresses. If the replication networks for the two systems involved in a replication link have both types of addresses, HCP uses the IP addresses for the first mode in which it can establish communication between the two systems, with preference given to IPv6.

Within a replication topology, different pairs of systems can use different IP modes for communication. The figure below shows a replication chain in which different IP modes are used for communication over each link.

GUID-181801A2-0327-4EEB-8810-7C51C4A8C1C2-low.png

In the topology shown above:

  • System A replicates to system B on link AB.
  • System B replicates to system C on link BC.
  • The replication network for system A has only IPv6 IP addresses.
  • The replication network for system B has both IPv4 IP address and IPv6 addresses.
  • The replication network for system C has only IPv4 IP addresses.
  • System A and system B use IPv6 addresses to communicate with each other.
  • System B and system C use IPv4 addresses to communicate with each other.
Loss of connectivity

You can select a different network for replication at any time. Selecting a different replication network on any given system can result in loss of connectivity to other systems with which that system is directly involved in replication.

When connectivity is lost between the two systems that participate in a replication link, the Replication service automatically suspends activity on that link. After restoring connectivity, you need to manually resume activity on the link.

For any given replication link, connectivity is lost between the two systems involved when you select a different network on one of the systems and either of these apply:

  • The networking infrastructure is not configured to route communications between the new network and the network selected for replication on the other system.
  • The new network is associated with a different domain from the previously selected network. In this case, the SSL server certificate used for replication changes, and you need to share the new certificate with the other system involved in the link.

    Additionally, in this case, if the system where you selected the new network is identified by domain name in the link configuration, you need to update the domain name in the link configuration.

In any case, if you select a different network on one system and the link identifies that system by IP addresses, you need to update those IP addresses in the link configuration.

If you need to both share new SSL server certificates and update the identification of one of the systems in the link configuration, you should share the certificates first. If you update the link first and then share the certificates, the link status changes to broken. To recover from this situation, you need to click again on Update Link in the Settings panel for the link.

Shared domain name

When you create a replication link, if both of the following are true, you need to use the replication.admin.hcp-domain-name format to identify the other system involved in the link:

  • You are identifying the other system by domain name.
  • The domain associated with the network selected for replication on the other system is also associated with another network.

In the configuration of an existing replication link, the domain name used to identify a system can have a format other than replication.admin.hcp-domain-name. In this case, you need to update the system identification to use the replication.admin.hcp-domain-name format if any of these happens on that system:

  • You change the domain associated with the replication network to a domain that’s also associated with another network.
  • You select a new replication network, and the new network is associated with a domain that’s also associated with another network.
  • You change the domain associated with another network to the domain that’s associated with the replication network.

Selecting the replication network

By default, HCP uses the [hcp_system] network for replication.

Procedure

  1. In the top-level menu of the HCP System Management Console, select Services Replication.

  2. On the left side of the Replication page, click Settings.

  3. On the replication Settings page, in the Replication Network field, select the network you want to use for replication traffic.

    The dropdown list of networks does not include empty, degraded, or partial networks.The Replication Network field is present only while virtual network management is enabled for the HCP system.
  4. Click Update Settings.

Displaying the zone definition for the replication network domain

Each network in HCP is associated with a domain. Multiple networks can be associated with the same domain. If you’re using DNS for domain name resolution, the DNS needs to include a zone definition for each combination of network and domain.

If an HCP system is involved in replication, the zone definition for the replication network domain for that system needs to be added to the upstream DNS servers for the other system on the replication link. An upstream DNS server is a DNS server to which HCP routes the outbound communications HCP initiates (for example, for sending log messages to syslog servers or for communicating with Active Directory).

If the domain for the replication network is shared with other networks, the domain name in the zone definition you add for the replication network domain must be:

replication.admin.replicaton-network-domain-name

From the Replication page, you can display the zone definition for the replication network domain, formatted for Unix DNS servers. You can then copy that definition to the upstream DNS servers.

NoteYou can display the zone definition only while virtual network management is enabled for the HCP system and only if at least one user-defined network exists.

Procedure

  1. In the top-level menu of the HCP System Management Console, select Services Replication.

  2. On the left side of the Replication page, click Settings.

  3. On the replication Settings page, click Zone Definition.

Results

The Zone Definition section opens. This section shows the zone definition for the network (with a type of slave or stub, as applicable), formatted as shown in this example:
# net1 Special-purpose HCP system network
zone "replication.admin.system_1.example.com" IN {
       type slave;
       file "/var/named/slave/replication.admin.system_1.example.com";
       masters {
             172.25.147.11;
             172.25.147.12;
             172.25.147.13;
             172.25.147.14;
       };
};

 

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