Information Technology Reference
In-Depth Information
Table 15-3 outlines the possible problem that might cause this symptom and describes solutions to that
problem.
Table15-3 Serial Lines: Increasing Input Drops on Serial Link
Possible Problem
Solution
Input rate exceeds
the capacity of the
router
,
or input
queues exceed the
size of output
queues
Note
: Input drop problems are typically seen when traffic is
being routed between faster interfaces (such as Ethernet, Token
Ring, and FDDI
1
) and serial interfaces. When traffic is light,
there is no problem. As traffic rates increase, backups start
occurring. Routers drop packets during these congested periods.
Input rate exceeds
the capacity of the
router
,
or input
queues exceed the
size of output
queues
(continued)
1.
Increase the output queue size on common destination
interfaces for the interface that is dropping packets. Use the
hold-queue
number
out
interface configuration command.
Increase these queues by small increments (for instance, 25
percent) until you no longer see drops in the
show interfaces
output. The default output hold queue limit is 100 packets.
2.
Reduce the input queue size, using the
hold-queue
number
in
interface configuration command, to force input drops to
become output drops. Output drops have less impact on the
performance of the router than do input drops. The default
input hold queue is 75 packets.
1.
FDDI = Fiber Distributed Data Interface
Serial Lines: Increasing Input Errors in Excess of 1 Percent of Total Interface
Traffic
If input errors appear in the
show interfaces serial
output (refer to Figure 15-1), there are several
possible sources of those errors. The most likely sources are summarized in Table 15-4.
Any input error value for cyclic redundancy check (CRC) errors, framing errors, or aborts
above 1 percent of the total interface traffic suggests some kind of link problem that should
be isolated and repaired.
Note
