Hi, I'm getting a lot of overruns on a gigabit ethernet interface of a Cisco 6509. The interfaces is connected to a server which has a gig network card. I believe overruns happen when data comes from the server at a rate which the switch port can't handle.
My first question is, if the NIC in the server is 1Gbps then how come it's transmitting at a higher rate than that (if that's what's happening)? The 6509 is a beefy box and I'd have thought it could cope with whatever was chucked at it. It's not overworked by any stretch of the imagination.
They are not shown as errors on the show interface output though which I'm puzzled about.
Do the overruns mean that the packets are actually dropped by the switch? If so then won't that meant that there will be a lot of TCP retransmissions?
I've monitored the traffic on the switchport and there's generally about 100 - 300Mbps coming from the server (MS Exchange server).
The interfaces on the server NIC and the switch port are hard coded to 1000 Full duplex. I was wondering if they should be set to auto as I seem to remember reading a while ago that this is recommended by Cisco as the autonegotiation with a GigEthernet interface negotiates other parameters besides speed and duplex (such as flow control).
Here's the show interface output (by the way it states the counters have never been cleared but the overruns are ticking up pretty fast all the same. I've cleared the counters on another interface connected to another Exchange server a couple of days ago and it's clocked up a load of overruns since then)
RDC-PRI#sh int gi8/10
GigabitEthernet8/10 is up, line protocol is up (connected)
Hardware is C6k 1000Mb 802.3, address is 000e.83b9.2e01 (bia 000e.83b9.2e01)
MTU 1500 bytes, BW 1000000 Kbit, DLY 10 usec,
reliability 255/255, txload 2/255, rxload 46/255
Encapsulation ARPA, loopback not set
input flow-control is off, output flow-control is desired
Clock mode is auto
ARP type: ARPA, ARP Timeout 04:00:00
Last input never, output 00:00:26, output hang never
Last clearing of "show interface" counters 3d05h
Input queue: 0/2000/8127861/0 (size/max/drops/flushes); Total output drops: 0
Queueing strategy: fifo
Output queue: 0/40 (size/max)
5 minute input rate 183552000 bits/sec, 38613 packets/sec
5 minute output rate 10998000 bits/sec, 19970 packets/sec
3197934213 packets input, 1904525434503 bytes, 0 no buffer
Received 7419 broadcasts (679 multicast)
0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 8127861 overrun, 0 ignored
0 watchdog, 0 multicast, 0 pause input
0 input packets with dribble condition detected
1682151323 packets output, 152965398501 bytes, 0 underruns
0 output errors, 0 collisions, 0 interface resets
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
Could it have anything to do with:
Server NIC drivers/card incompatibility?
Switch IOS/firmware update needed?
Thanks in advance