pause input on 6509 gig interface

[DARYLE DIANIS]

I have an interface with the pause input counter incrementing often, I think. over 50 in 8 minutes. But I don't know for sure if this is a problem, the output interpreter doesn't say anything. Sounds like I'm oversubsribed? its an uplink to a 7204 router with an oc3 on it.

[Yudong Wu]

Pause input counter incrementing means that the port is receving pause frame. Pause frame is a packet that tells the far-end device to stop transmitting packets until the sender is able to handle all the traffic

and clear it's buffers. It could be caused by a oversubscription of bandwidth, or a burst traffic pattern.

[DARYLE DIANIS]

Hi thanks, I'm still a little puzzled. The switch interface is gigabit connected to a router with a gigabit interface. It seems like they should be able to keep up with each other. I've included two show interface commands. the router interface shows 18 pause input, and the switch shows 71 input errors and over runs. If both interfaces are rated at gigabit, why would either one have input errors due to oversubscription?

thanks,

[DARYLE DIANIS]

sorry about that, here's the show commands,,,,

router1#sho int g0/1

GigabitEthernet0/1 is up, line protocol is up

Hardware is BCM1250 Internal MAC, address is 0019.557f.ad1b (bia 0019.557f.ad1b)

Internet address is xxx.xxx.xxx.x/24

MTU 1500 bytes, BW 1000000 Kbit, DLY 10 usec,

reliability 255/255, txload 1/255, rxload 7/255

Encapsulation ARPA, loopback not set

Keepalive set (10 sec)

Full-duplex, 1000Mb/s, media type is RJ45

output flow-control is XON, input flow-control is XON

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 00:01:45

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

Queueing strategy: fifo

Output queue: 0/40 (size/max)

30 second input rate 28804000 bits/sec, 3820 packets/sec

30 second output rate 2512000 bits/sec, 2376 packets/sec

507152 packets input, 511041612 bytes, 0 no buffer

Received 49 broadcasts, 0 runts, 0 giants, 0 throttles

71 input errors, 0 CRC, 0 frame, 71 overrun, 0 ignored

0 watchdog, 163 multicast, 0 pause input

0 input packets with dribble condition detected

307671 packets output, 35962455 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

ymusrtr1#

switch1#sho int g1/26

GigabitEthernet1/26 is up, line protocol is up (connected)

Hardware is C6k 1000Mb 802.3, address is 0014.a86c.faa9 (bia 0014.a86c.faa9)

Description: 7204 g0/1

MTU 1500 bytes, BW 1000000 Kbit, DLY 10 usec,

reliability 255/255, txload 10/255, rxload 1/255

Encapsulation ARPA, loopback not set

Keepalive set (10 sec)

Full-duplex, 1000Mb/s

input flow-control is off, output flow-control is on

Clock mode is auto

ARP type: ARPA, ARP Timeout 04:00:00

Last input 00:00:47, output 00:00:55, output hang never

Last clearing of "show interface" counters 00:02:43

Input queue: 0/2000/0/0 (size/max/drops/flushes); Total output drops: 0

Queueing strategy: fifo

Output queue: 0/40 (size/max)

5 minute input rate 2920000 bits/sec, 3121 packets/sec

5 minute output rate 42425000 bits/sec, 4721 packets/sec

489623 packets input, 59540773 bytes, 0 no buffer

Received 37 broadcasts (37 multicasts)

0 runts, 0 giants, 0 throttles

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

0 watchdog, 0 multicast, 18 pause input

0 input packets with dribble condition detected

785393 packets output, 811507207 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

ymuscrswa#

[Yudong Wu]

Yes, it could happen when both sides are in the same speed.

From the info you provided, the router side can not handle the packet sending from switch. So router sent PAUSE "flow-control packet" to switch to ask it slow down. That't why we saw "overrun" on router side and "pause input" on switch.

There are multiple reasons which could be contributed to this, such as micro burst traffic, RX and TX buffer size on each side, or/and if the router is too busy to handle the packet quickly enough at certain time.

[DARYLE DIANIS]

ok, looking farther into the network, I guess this could be the result of my serial line on the router not being able to keep up?

[Yudong Wu · Accepted solution]

Possible, but I can not say for sure without knowing detail.

But one thing clear is that the router can not pass/handle the packets sending from the switch quickly.

If your serial line has issue such as flapping, it might cause your routing protocol flapping, As a result router is busy on routing reconvergence calculation...