Installing and Administering LAN/9000 Software

Chapter 4 81
Troubleshooting LAN/9000
Diagnostic Flowcharts
Figure 4-1 Loopback Tests
The loopback tests shown in Figure 4-1 are used to isolate a network
communication problem that may be software- or hardware-related. In
any case, you should first have checked that the problem is not due to a
recent configuration change.
The network level loopback test, ping(1M), commonly is tried first. It is
fast, efficient, and it does not require super-user privileges. If the
connection passes this test, you know the problem is at OSI Layer 4 or
above. Go on to the transport level loopback test.
The Transport Level Loopback Test can be implemented using Internet
Services. In this case, you use telnet and ftp to systematically focus on
a problem.
If the network level loopback test failed, the problem is in OSI Layer 3 or
below. In this case, continue with the link level loopback test,
linkloop(1M), to isolate a problem to OSI Layer 2 or below.
UDP
IP
LAN Driver
Network Interface Card
ARP
TCP
BSD Sockets
Virtual
NFS Services
DLPI
Terminal
Internet Services
1
2
3
6 & 7
5
4
ping
linkloop
lanadmin
ICMP
MAU
XTI
OSI Layer
telnet showmount
(NFS)