Information Technology Reference
In-Depth Information
Isolating Clocking Problems
After you determine that clocking conflicts are the most likely cause of input errors, use the following
procedure to isolate the source of those errors:
Step 1
Perform a series of
ping
tests and loopback tests (both local and remote), as described in the section
“CSU and DSU Loopback Tests,” earlier in this chapter.
Step 2
Determine which end of the connection is the source of the problem, or whether the problem is in the
line. In local loopback mode, run different patterns and sizes in the
ping
tests (for example, use
1500-byte datagrams). Using a single pattern and packet size may not force errors to materialize,
particularly when a serial cable to the router or CSU/DSU is the problem.
Step 3
Use the
show interfaces serial
exec command, and determine whether input errors counts are increasing
and where they are accumulating.
If input errors are accumulating on both ends of the connection, clocking of the CSU is the most likely
problem.
If only one end is experiencing input errors, there is probably a DSU clocking or cabling problem.
Aborts on one end suggest that the other end is sending bad information or that there is a line problem.
Always refer to the
show interfaces serial
command output (see Figure 15-1). Log any
changes in error counts, or note if the error count does not change.
Note
