Have a pair of 2960's in a stack, one port(trunk) connects to another DC and we are seeing ~5% packet-loss
and large output drops to this DC.
#sh interfaces gigabitEthernet 1/0/17 counters errors
Port Align-Err FCS-Err Xmit-Err Rcv-Err UnderSize OutDiscards
Gi1/0/17 0 0 0 0 0 182867
GigabitEthernet1/0/17 is up, line protocol is up (connected)
Hardware is Gigabit Ethernet, address is a0cf.5b87.ec11 (bia a0cf.5b87.ec11)
Description: QinQ_to_DC2
MTU 1998 bytes, BW 100000 Kbit, DLY 100 usec,
reliability 255/255, txload 41/255, rxload 23/255
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 6d13h, output 00:00:00, output hang never
Last clearing of "show interface" counters 04:02:15
Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 183592
Queueing strategy: fifo
Output queue: 0/40 (size/max)
30 second input rate 9047000 bits/sec, 2075 packets/sec
30 second output rate 16324000 bits/sec, 2309 packets/sec
As you can see, 30sec rate isnt excessive, but as the drops are outdiscards it would appear we are getting hit by the small buffers/microburst issue.
Gi1/0/17 is mapped to asic 0/20
Gi1/0/17 17 17 17 0/20 1 17 17 local Yes Yes
Port-asic Port Drop Statistics - Summary
========================================
Port 20 TxQueue Drop Stats: 308277833
And majority appear to be in Queue 1:
Port 20 TxQueue Drop Statistics
Queue 0
Weight 0 Frames 3
Weight 1 Frames 0
Weight 2 Frames 0
Queue 1
Weight 0 Frames 308240408
Weight 1 Frames 458
Weight 2 Frames 0
Queue 2
Weight 0 Frames 37898
Weight 1 Frames 0
Weight 2 Frames 0
Queue 3
Weight 0 Frames 91
Weight 1 Frames 0
Weight 2 Frames 0
Queue 4
Weight 0 Frames 0
Weight 1 Frames 0
Weight 2 Frames 0
Queue 5
Weight 0 Frames 0
Weight 1 Frames 0
Weight 2 Frames 0
Queue 6
Weight 0 Frames 0
Weight 1 Frames 0
Weight 2 Frames 0
Queue 7
Weight 0 Frames 0
Weight 1 Frames 0
Weight 2 Frames 0
Done a bit of reasearch, and as we have mls qos configured(we have some ssh/rdp policies in place on access-ports), we need to look at "tweaking" the buffer allocations on the switch to hopefully mitigate(reduce) these drops.
There appears to be a range of recommendations when it comes to these tweaks - Hoping someone has some suggestions on
what to set with "mls qos queue-set output" to alleviate the drops?(start conservative, then apply more aggressive if needed)....and also, does adjusting the buffers require an outage window?
Our traffic is primarily backup(replication which is very bursty), and Internet
Thanks in advance.
