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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 Cluster Addressing Scheme Node Address Triplets Floating Address Triplet ## 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 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, `NIC` 0 and `NIC` 1 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 `hme` 0 | Address for Physical Interface `hme` 1 | Address for Virtual Interface `cgtp` 0
--- | --- | --- | ---
Master Node | `10.200.1.10` | `10.200.2.10` | `10.200.3.10`
Vice-Master Node | `10.200.1.11` | `10.200.2.11` | `10.200.3.11`
Diskless Node 1 | `10.200.1.12` | `10.200.2.12` | `10.200.3.12`
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 ## 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 `hme` 0 or `cgtp` 0 interface has the format `hme` 0:x or `cgtp` 0: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 | `hme` 0 | `10.200.1.10`
Physical | `hme` 1 | `10.200.2.10`
Virtual Physical | `cgtp` 0 | `10.200.3.10`
Floating Address Triplet | Logical | `hme` 0:1 | `10.200.1.1`
Logical | `hme` 1:1 | `10.200.2.1`
Virtual Logical | `cgtp` 0:1 | `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 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
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