Serial INterface Out Put Drops

Unanswered Question
Apr 13th, 2008

Hi I am having 128 kbps MPLS link. I am getting out drops 5528 I have reported with ISP but they are saying problem with router. I have changed the WIC card and before I user 1700 router I tried to changed the 1841 router but the same out put drops is there. Users are facing slow performance while accessing the internet Application. I have checked the bandwidth utilization also its between 128 kbps only. Please help any one

MTU 1500 bytes, BW 128 Kbit, DLY 20000 usec,

reliability 255/255, txload 97/255, rxload 61/255

Encapsulation HDLC, loopback not set

Keepalive set (10 sec)

CRC checking enabled

Last input 00:00:03, output 00:00:00, output hang never

Last clearing of "show interface" counters 06:39:34

Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 5528

Queueing strategy: weighted fair

Output queue: 0/1000/64/5528 (size/max total/threshold/drops)

Conversations 0/8/32 (active/max active/max total)

Reserved Conversations 0/0 (allocated/max allocated)

Available Bandwidth 96 kilobits/sec

30 second input rate 31000 bits/sec, 47 packets/sec

30 second output rate 49000 bits/sec, 78 packets/sec

563334 packets input, 50369231 bytes, 0 no buffer

Received 2394 broadcasts, 0 runts, 0 giants, 0 throttles

6 input errors, 6 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort

915177 packets output, 73442263 bytes, 0 underruns

0 output errors, 0 collisions, 0 interface resets

0 output buffer failures, 0 output buffers swapped out

0 carrier transitions

DCD=up DSR=up DTR=up RTS=up CTS=up

I have this problem too.
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Hi, I read your post and when you see output drops it is because packet are being dropped going out of the interface. The mose common reason is that the buffers on the receiving end are full and the output hold queue on your interface drops the packets. You can increase the output hold queue with the "hold-queue out" command, use this command with caution changing the queue size can cause other problems. have a read of the document posted below it should help you resolve this problem. HTH


Table 15-2 Serial Lines: Increasing Output Drops on Serial Link

Possible Problem Solution

Input rate to serial interface exceeds bandwidth available on serial link

1. Minimize periodic broadcast traffic, such as routing and SAP1 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.

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 IPX2 ). 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


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