Information Technology Reference
In-Depth Information
Table 15-2 outlines the possible problem that might cause this symptom and describes solutions to that
problem.
Table15-2 Serial Lines: Increasing Output Drops on Serial Link
Possible Problem
Solution
Input rate to serial
interface exceeds
bandwidth
available on serial
link
Minimize periodic broadcast traffic, such as routing and
SAP
1
updates, by using access lists or by other means. For
example, to increase the delay between SAP updates, use the
ipx sap-interval
interface configuration command.
1.
Input rate to serial
interface exceeds
bandwidth
available on serial
link
(continued)
2.
Increase the output hold queue size in small increments (for
instance, 25 percent), using the
hold-queue out
interface
configuration command.
3.
On affected interfaces, turn off fast switching for heavily
used protocols. For example, to turn off IP fast switching,
enter the
no ip route-cache
interface configuration
command. For the command syntax for other protocols,
consult the Cisco IOS configuration guides and command
references.
4.
Implement priority queuing on slower serial links by
configuring priority lists. For information on configuring
priority lists, see the Cisco IOS configuration guides and
command references.
Note:
Output drops are acceptable under certain conditions. For
instance, if a link is known to be overused (with no way to
remedy the situation), it is often considered preferable to drop
packets than to hold them. This is true for protocols that support
flow control and can retransmit data (such as TCP/IP and Novell
IPX
2
). However, some protocols, such as DECnet and local-area
transport, are sensitive to dropped packets and accommodate
retransmission poorly, if at all.
1.
SAP = Service Advertising Protocol
2.
IPX = Internetwork Packet Exchange
Serial Lines: Increasing Input Drops on Serial Link
Input drops appear in the output of the
show interfaces serial
exec command (refer to Figure 15-1) when
too many packets from that interface are still being processed in the system.
Symptom:
Increasing number of input drops on serial link
