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Chapter 4

Cluster Addressing

For a description of how a Foundation Services cluster can be addressed, see the following sections:

Introduction to Cluster Addressing

Peer nodes communicate with each other over a private network, called the cluster network.

The addressing scheme used by the cluster network is classless. The IP addresses of peer nodes can be in a private network or a public network. It is advantageous to configure a cluster in a private network for the following reasons:

  • There is no need to allocate addresses from a public address space for each cluster.

  • External data can be added into or taken out of the cluster network in a controlled way, making the cluster network more secure.

  • The cluster network cannot be overloaded by external traffic.

  • The redundant network symmetry is protected.

Cluster Addressing Scheme

All peer nodes are assigned IPv4 addresses. The address is split into a network part and a host part. The dividing point between the network part and the host part is defined by the netmask.

The following figure illustrates the structure of an IP address on a peer node.

Figure 4-1 Structure of an IP Address on a Peer Node

Figure illustrates the network part and host part of an IP address

The network part of an IP address represents the identity of the network to which a peer node is connected. The host part of an IP address represents the nodeid of the peer node. The nodeid is the decimal equivalent of the host part of the IP address.

In a class B addressing scheme, the value of the netmask is ffff0000. The network part of an IP address is 16 bits long, and the host part of an IP address is 16 bits long.

In the class C addressing scheme, the value of the netmask is ffffff00. The network part of an IP address is 24 bits long, and the host part of an IP address is 8 bits long. By default, a class C address on a Foundation Services cluster has the following format:

10.domainid.interfaceid.nodeid

The Foundation Services can use a classless addressing scheme. The value of the netmask is not restricted to any address class.

The following values of the host part of the IP address are reserved:

  • Value "0" is reserved for the identification of the network part of the IP address.

  • Value "1" is reserved for the floating address triplet. For information about the floating address triplet, see Floating Address Triplet.

  • Value 2n-1 is reserved for the broadcast address. The parameter n is the number of bits in the host part of the IP address.

Node Address Triplets

A node address triplet is assigned to each peer node in a cluster. The node address triplet consists of three IP addresses:

  • An IP address for each of the two physical interfaces, NIC0 and NIC1

  • An IP address for the virtual interface, called the CGTP address

The CGTP address is used for IP routing. It hides the multirouting capability of CGTP. The CGTP address presents the redundant network as a single network interface. Applications can use the CGTP address to communicate with the master node. The CGTP address supports unicast, broadcast, and multicast transmissions. For more information about CGTP, see Chapter 6, Carrier Grade Transport Protocol.

The following table shows an example of node address triplets for a cluster containing two master-eligible nodes and two diskless nodes. The cluster uses a default class C addressing scheme.

Table 4-1 Example of Node Address Triplets for a Four-Node Cluster

Node Name Address for Physical Interface hme0Address for Physical Interface hme1Address for Virtual Interface cgtp0
Master Node 10.200.1.1010.200.2.1010.200.3.10
Vice-Master Node 10.200.1.1110.200.2.1110.200.3.11
Diskless Node 1 10.200.1.1210.200.2.1210.200.3.12
Diskless Node 2 

10.200.1.13

10.200.2.13

10.200.3.13

The following figure shows the address triplets of the preceding cluster.

Figure 4-2 Node Address Triplets

Diagram shows the address triplets in a four node cluster

Floating Address Triplet

In addition to a node address triplet, the master node and vice-master node have an address triplet called the floating address triplet. The floating address triplet is activated on the master node only. If the master node fails over or is switched over, the floating address triplet is activated on the new master node. It is deactivated on the old master node.

Diskless nodes and dataless nodes access services and data on the master node, through the floating address triplet. Because the floating address triplet is always up on the master node, the diskless nodes and dataless nodes can access the master node even after a failover or switchover.

The floating address triplet has a logical address. A logical address is an address that is assigned to a physical interface or virtual interface. A logical address for an hme0 or cgtp0 interface has the format hme0:x or cgtp0:x.

The following table shows an example of the node address triplet and floating address triplet of a master node. The cluster is using a default class C addressing scheme.

Table 4-2 Example of Master Node Address Triplets

Triplet Type

Address Type

Interface Address Example 

Node Address Triplet

Physical

hme0

10.200.1.10

Physical

hme1

10.200.2.10

Virtual Physical

cgtp0

10.200.3.10

Floating Address Triplet

Logical

hme0:1

10.200.1.1

Logical

hme1:1

10.200.2.1

Virtual Logical

cgtp0:1

10.200.3.1

Figure 4-3 shows the node address triplet and floating address triplet of the master node and vice-master node. The diskless nodes are mounted onto the master node. The floating address triplet of the vice-master node is barred out because it is down.

Figure 4-3 Example of the Floating Address Triplet of a Master Node and Vice-Master Node

Diagram shows an example of the node address triplet and floating address triplet of a master node, and the diskless nodes mounted onto the master node.

Figure 4-4 shows the cluster in Figure 4-3 after a failover. The diskless nodes are mounted onto the new master node.

Figure 4-4 Example of the Floating Address Triplet After Failover

Diagram shows an example of the diskless nodes mounted onto the new master node after a failover.
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