HP XC System Software Administration Guide Version 3.1

9 Network Administration
This chapter addresses the following network topics:
• “Network Address Translation Administration” (page 125)
• “Network Time Protocol Service” (page 126)
• “Changing the External IP Address of a Head Node” (page 127)
• “Modifying Sendmail” (page 127)
9.1 Network Address Translation Administration
Network Address Translation (NAT) enables compute nodes that do not contain external devices to have
external network access.
Packets from compute nodes that are destined for the external network are sent to a NAT server, which
rewrites the source address of the packet to make it look as if the NAT server sent the packet.
If a NAT server fails, the compute nodes using the NAT server need a way to continue sending packets
on the external network while the original NAT server is unavailable. The means by which NAT functions
differs depending on whether or not improved availability is in effect.
Improved Availability Is in Effect
Nodes in an availability set, that are assigned with the external role, are eligible to be NAT servers. The
availability set is defined during installation.
Each NAT client connects to a NAT server through a virtual IP address.
If a NAT server fails, the availability tool reassigns its virtual IP address to another node in the nat
availability set, and the nat service continues.
Figure 9-1 shows two nodes, n5 and n6 that belong to an availability set. Before failover, node n2, a NAT
client, accesses the nat service on node n5 through the virtual IP address. After failover, the virtual IP
address is reassigned to node n6, which now provides the nat service for node n5 clients as well as to all
the other nodes it serves.
Figure 9-1 NAT Service Under Improved Availability
Improved Availability Is Not in Effect
You establish the external role assignment when you configure the HP XC system using the
cluster_config utility.
9.1 Network Address Translation Administration 125