Output Drops

[giorgikukulava]

Hello I have many output drops as router as switch how can I fix this ?

R1#show int gig 4
GigabitEthernet4 is up, line protocol is up
Hardware is iGbE, address is 0087.6466.6fa0 (bia 0087.6466.6fa0)
Internet address is ***********/30
MTU 1500 bytes, BW 100000 Kbit/sec, DLY 100 usec,
reliability 255/255, txload 1/255, rxload 11/255
Encapsulation ARPA, loopback not set
Keepalive set (10 sec)
Full Duplex, 100Mbps, media type is RJ45
output flow-control is unsupported, input flow-control is unsupported
ARP type: ARPA, ARP Timeout 04:00:00
Last input 00:00:00, output 00:00:00, output hang never
Last clearing of "show interface" counters never
Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 2041
Queueing strategy: fifo
Output queue: 0/40 (size/max)
5 minute input rate 4689000 bits/sec, 605 packets/sec
5 minute output rate 560000 bits/sec, 403 packets/sec
83237148 packets input, 81051846606 bytes, 0 no buffer
Received 15335 broadcasts (0 IP multicasts)
0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
0 watchdog, 0 multicast, 0 pause input
57087185 packets output, 8748139086 bytes, 0 underruns
0 output errors, 0 collisions, 0 interface resets
0 unknown protocol drops
0 babbles, 0 late collision, 0 deferred
24 lost carrier, 0 no carrier, 0 pause output
0 output buffer failures, 0 output buffers swapped out

SW

GigabitEthernet1/0/7 is up, line protocol is up (connected)
Hardware is Gigabit Ethernet, address is 6886.a7b6.3507 (bia 6886.a7b6.3507)
MTU 1500 bytes, BW 100000 Kbit, DLY 100 usec,
reliability 255/255, txload 17/255, rxload 14/255
Encapsulation ARPA, loopback not set
Keepalive set (10 sec)
Full-duplex, 100Mb/s, media type is 10/100/1000BaseTX
input flow-control is off, output flow-control is unsupported
ARP type: ARPA, ARP Timeout 04:00:00
Last input 00:00:00, output 00:00:00, output hang never
Last clearing of "show interface" counters never
Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 88315
Queueing strategy: fifo
Output queue: 0/40 (size/max)
5 minute input rate 5651000 bits/sec, 2975 packets/sec
5 minute output rate 6993000 bits/sec, 2346 packets/sec
51181964 packets input, 19296502121 bytes, 0 no buffer
Received 402116 broadcasts (336284 multicasts)
0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
0 watchdog, 336284 multicast, 0 pause input
0 input packets with dribble condition detected
102677726 packets output, 125143810980 bytes, 0 underruns

[Georg Pauwen]

Hello,

compared to the total amount of packets, the number of output drops is very, very small. Output drops occur when the output queue is full. On a layer 3 interface, you could implement some sort of QoS involving shaping, but given the tiny amount of drops, it probably wouldn't make a difference. Are your users experiencing problems ?

[Joseph W. Doherty]

Georg is correct, that overall your drop stats aren't really high. However, it's possible they are high during very short time intervals. (So, he asks an important question, i.e. are users having problems.)

Since you're 5 minute bandwidth stats show a load average of under 10%, it's possible bursts, perhaps even micro-bursts, are overrunning your egress queues.

Do you know your BDP (bandwidth delay product)? If (when) you do, set your egress buffer resources to about half your BDP. On the router, that might be done simply by setting interface's egress queue max size. On the switch, how to allocate egress queue resources depends on the particular model (and possibly on how its already configured).