Computer Hardware User Manual

62 IBM Certification Study Guide AIX HACMP
To comply with these rules, pay careful attention to the IP addresses you
assign to standby adapters. Standby adapters
must be on a separate subnet
from the service adapters, even though they are on the same physical
network. Placing standby adapters on a different subnet from the service
adapter allows HACMP for AIX to determine which adapter TCP/IP will use to
send a packet to a network.
If there is more than one adapter with the same network address, there is no
way to guarantee which of these adapters will be chosen by IP as the
transmission route. All choices will be correct, since each choice will deliver
the packet to the correct network. To guarantee that only the service adapter
handles critical traffic, you must limit IP’s choice of a transmission route to
one adapter. This keeps all traffic off the standby adapter so that it is
available for adapter swapping and IP address takeover (IPAT). Limiting the
IP’s choice of a transmission route also facilitates identifying an adapter
failure.
See Chapter 2.4.3, “IP Address Takeover” on page 34 for more detailed
information.
3.2.1.3 Testing
After setting up all adapters with AIX, you can do several things to check
whether TCP/IP is working correctly. Note, that without HACMP being started,
the service adapters defined to HACMP will remain on their boot address.
After startup these adapters change to their service addresses.
Use the following AIX commands to investigate the TCP/IP subsystem:
• Use the
netstat command to make sure that the adapters are initialized
and that a communication path exists between the local node and the
target node.
• Use the
ping command to check the point-to-point connectivity between
nodes.
• Use the
ifconfig command on all adapters to detect bad IP addresses,
incorrect subnet masks, and improper broadcast addresses.
The netmask for all adapters in an HACMP network must be the same even
though the service and standby adapters are on different logical subnets.
See the
HACMP for AIX, Version 4.3: Concepts and Facilities, SC23-4276
guide for more information about using the same netmask for all adapters.
Note