Interface RX pause

[Geir Sand-Strand]

Hi

I have 2 Nexus 5672 running in vpc.  I'm running Eth1/5 on both i port-channel towards an 7004 (port eth3/1 and 3/2 in port-channel).

On one of the 5k's eth1/5 port i see rx pause increase a lot.  None of the other physcal interfaces increases the rx pause.

N5K-1# sh int eth1/5 | inc pause
    650251486 Rx pause

How can I troubleshoot this and find a soultion to get rid of the rx pause increasing?

Config of the 4 ports and port-channel looks like this (nothing fancy):

interface Ethernet1/5
  description N7K
  switchport mode trunk
  switchport trunk native vlan 998
  switchport trunk allowed vlan 181-183,185,500,504-505,508,514,550-551,555-556,699-700,2196
  channel-group 50 mode active

interface port-channel50
  description N7K
  switchport mode trunk
  switchport trunk native vlan 998
  switchport trunk allowed vlan 181-183,185,500,504-505,508,514,550-551,555-556,699-700,2196
  speed 10000
  vpc 50

(same on both 5k's)

On the N7K:

interface Ethernet3/1
  description N5K-1
  switchport
  switchport mode trunk
  switchport trunk native vlan 998
  switchport trunk allowed vlan 181-183,185,500,504-505,508,514,550-551,555-556,699-700,2196
  spanning-tree port type network
  mtu 9216
  channel-group 1 mode active
  no shutdown

interface Ethernet3/2
  description N5K-2
  switchport
  switchport mode trunk
  switchport trunk native vlan 998
  switchport trunk allowed vlan 181-183,185,500,504-505,508,514,550-551,555-556,699-700,2196
  spanning-tree port type network
  mtu 9216
  channel-group 1 mode active
  no shutdown

interface port-channel1
  description N5K's
  switchport
  switchport mode trunk
  switchport trunk native vlan 998
  switchport trunk allowed vlan 181-183,185,500,504-505,508,514,550-551,555-556,699-700,2196
  mtu 9216

[Andrea Testino]

Hi Geir,

An RX Pause indicates the Nexus 5K is receiving Pause Frames from the Nexus 7000 - This means that Nexus 7000 is experiencing congestion and is sending Pause frames to the N5K to slow down. Assuming flowcontrol is configured throughout the path, the N5K will attempt to buffer the traffic on its end as much as possible before discarding it.

Pause Frames are not necessarily something to worry about as the alternative is to drop the traffic from the get go instead. A way to mitigate this however would be to add more bandwidth to this particular port-channel. Are you seeing any discards/errors on the Nexus 7000 side?

Hope that helps,

- Andrea

[Geir Sand-Strand]

No, I don't see any error or discards on the N7K side.  It's only Eth1/5 on one of the N5K's showing rx pause. And it is counting upwards rater quickly. Flow control is not configured on the interfaces.

[chenfei]

i also have this question ,but in my problem,the N7k is a Server run oracle rack,i guess the reason is jumbo mtu .