Output Drops

[Robo123]

All,

I am experiencing Heavy output drops on my Cisco3945 Router interface.

GigabitEthernet0/1 is up, line protocol is up
Hardware is PQ3_TSEC, address is *.*.*.*
MTU 1500 bytes, BW 1000000 Kbit/sec, DLY 10 usec,
reliability 255/255, txload 6/255, rxload 1/255
Encapsulation 802.1Q Virtual LAN, Vlan ID 1., loopback not set
Keepalive set (10 sec)
Full Duplex, 1Gbps, media type is SX
output flow-control is unsupported, input flow-control is unsupported
Last clearing of "show interface" counters 06:18:57
Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 14680
Queueing strategy: fifo
Output queue: 0/40 (size/max)
30 second input rate 1573000 bits/sec, 269 packets/sec
30 second output rate 25628000 bits/sec, 2375 packets/sec
8566464 packets input, 7564357359 bytes, 0 no buffer
Received 294192 broadcasts (0 IP multicasts)
0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
0 watchdog, 149951 multicast, 0 pause input
61978541 packets output, 80516756110 bytes, 0 underruns
0 output errors, 0 collisions, 0 interface resets
0 unknown protocol drops
0 babbles, 0 late collision, 0 deferred
0 lost carrier, 0 no carrier, 0 pause output
0 output buffer failures, 0 output buffers swapped out

show cef drop

IPv4 CEF Drop Statistics
Slot   Encap_fail  Unresolved   Unsupported    No_route   No_adj   ChkSum_Err
RP           0                 0            11986544            0               0              0

sh ip cef switching statistics feature

IPv4 CEF input features:
Feature                          Drop   Consume Punt  Punt2Host   Gave route
IP not enabled d       1717684        0          0        0                0
Total                         1717684        0          0        0                0

[marce1000]

 https://www.cisco.com/c/en/us/support/docs/routers/10000-series-routers/6343-queue-drops.html

 M.

[Joseph W. Doherty]

14680/61978541 = (about) .02 percent, which isn't generally considered a "heavy" drop percentage.

That said, you might have transient microbursts, and so increasing your output queue, from the default of 40, might mitigate your drops. NB: TCP looks for a buffer size based on the BDP (bandwidth delay product); usually you don't need to go beyond half of that for the router's interface.