HP XC System Software Administration Guide Version 3.1

When nodes are configured as NAT clients, the default gateways are established. By default, each NAT
client has a single gateway. If a NAT server fails, however, the NAT client loses connectivity.
You can configure a system for multiple gateways to lessen the possibility of loss of connectivity, but the
system may have performance problems. External access from NAT clients using UDP has been shown
to work well, however. Use the following procedure to create a NAT client configuration with multiple
default gateways.
1. Ensure that all available software patches for this release have been applied to the system.
2. Use the dbsysparams command to modify the value of NAT_GATEWAYS from single to multiple:
# /opt/hptc/sbin/dbsysparams "NAT_GATEWAYS"
NAT_GATEWAYS: single
# /opt/hptc/sbin/dbsysparams -s "NAT_GATEWAYS" "multiple"
3. Use the dbsysparams command to verify the results:
# /opt/hptc/sbin/dbsysparams "NAT_GATEWAYS"
NAT_GATEWAYS: multiple
4. Rerun the nconfig and cconfig commands to create the /etc/init.d/default_gateway file
on each node so that the file contains multiple default gateway definitions:
# pdsh -a "service nconfig nconfigure"
# pdsh -a "service nconfig nrestart"
When multiple NAT gateways are used, the NAT configuration code creates logical pairs of NAT servers
from the usable NAT servers for the client as a way to coordinate clients and servers. During NAT client
configuration, the /etc/init.d/default_gateway script is created on each NAT client. This script
contains the calls to add the default gateways for the client; this is how the NAT client identifies which
NAT server is assigned to it.
The following kernel values in the /etc/init.d/default_gateway script control how frequently the
route table is rewritten and reevaluated:
sysctl net/ipv4/route/gc_timeout=10 > /dev/null
sysctl net/ipv4/route/secret_interval=10 > /dev/null
Clients reevaluate their routes on a regular basis, balancing the usage between the NAT servers; thus, a
particular client could be using either of the two NAT servers at any particular time. Use the traceroute
command to determine which of the NAT servers configured in the /etc/init.d/default_gateway
script serves a given client at a given time.
9.2 Network Time Protocol Service
By default, the head node acts as the primary Network Time Protocol (NTP) internal server for all other
nodes in an HP XC system. Other nodes are NTP clients of the head node.
You can specify where the NTP server obtains its time reference during the initial configuration of the HP
XC system; up to three external time servers are accepted if the internal server is connected to an external
network. You can also specify the internal server's clock as the time reference instead.
If you encounter a clock synchronization problem, examine the /etc/ntp.conf file on the internal server
and the /etc/ntp.conf file on the node that is experiencing the problem.
You can restart the NTP service (ntpd) with the following command:
# service ntpd restart
Other tools (ntpq and ntpdc) are also available. For more information on NTP, see ntpd(1), ntpdc(1), and
ntpq(1).
126 Network Administration