HP XC System Software Administration Guide Version 3.2

9 Network Administration
This chapter addresses the following network topics:
• “Network Address Translation Administration” (page 131)
• “Network Time Protocol Service” (page 132)
• “Changing the External IP Address of a Head Node” (page 133)
• “Modifying Sendmail” (page 133)
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
9.1 Network Address Translation Administration 131