Switching

Dear Team,

We have EX-3400 devices as a access layer switches.DHCP is configured in CORE devices(CISCO).When we connect end devices(PC,laptops,IP phone), we are unable to get DHCP IP addresses due to increment of MAC pause frames on some of the interfaces, and when we connect door security devices ,intermittent packet drops are observed.

Please let us know how to fix this issue permanently ,apart from rebooting the device.As we tried reboot,issue resolved temporarily but again issue occured.

Thanks and regards,

Abhijith Goud Pabba.

try to disable flow-control on interfaces

I might suggested  that MAC Pause Frames may not be the source of DHCP not working.  MAC Pause Frames should only be associated with 10GE ports, so I assume these are related to using 10GE uplink ports to connect to the Cisco, or might you be using 40GE interfaces for this connection?  BTW, the pause frames, I assume, are coming from the Cisco - have you asked them why this is happening?

If you set a static IP on a [test] device off of the 1GE ports of the EX3400, can it ping the Cisco IP in the same subnet/vlan?  Is the connection to the Cisco a tagged trunk port, or access?  Is this new install, or are the EX3400s replacing older other Cisco gear, and if yes, did DHCP function properly prior to replacememt?  On EX3400 have you enabled any port level security features?

There are probably 5 other questions I have not asked, . . .  Do you have a TAC case opened, or no service contract?

Hi Abhijith,

MAC pause frame increases when flow control mechanism is enabled and the PFE is not able to handle all the traffic probably becuase the buffers are full as the traffic is coming at very high rate/burst. In order to avoid any drops in such situation the device send MAC pause so that the connected device doesn't send any traffic for some time. 

Refer KB:    https://kb.juniper.net/KB23817

You can try to disbale the flow control mechanism on the port using following command:

set interfaces ge-0/0/24 ether-options no-flow-control

Once you have disbaled the flow-control it will reflect in "show interface ge-0/0/24 extensive" output and you shouldn't see any increment in MAC pause frame.

PS: Please accpet my response as solution if it answers your query, kuods are appreicated too!

Thanks
Vishal

Hi abhijith,

I don't think that MAC pause frames are the root cause but the consequence. Please check if you are experiencing high levels of traffic that might be starving your CPU memory a few questions, How is the CPU looking at the time the issue is happening? When did the issue start? Any hardware or software changes? Whats the version you are running?

Regards, 

I doubt CPU would or should be involved.  This should happen at the PFE.  #1 question - are you seeing receive or transmit Pause Frames on the EX3400?  I assume receive, which means the Cisco is saying slow down transmit, but I am not sure why.  You would need to ask Cisco that question.

You're likely running into PR1452209. If you look at the interfaces in question you'll likely notice that they negotiate at half-duplex.

There's a problem with the Resolved In field of the PR view - this problem is not yet resolved but is erroneously displaying several releases (18.3R3-S1, 18.4R3, 19.1R3 and 19.2R2) under the Resolved In section. I will fix this.

This problem is currently pending a fix from the chipset manufacturer.

-Alper

Hi Abhijith,

Please let me know if the security devices you mentioned only support half-duplex connectivity.

If they are and you are running code 18.X +, then you are probably running into a known issue which is being actively worked on. 

Work around: set the speed and duplex manually matching the other end device.

If the other end device supports full-duplex, the above does not apply.

Please let me know your findings.

Thank you,

regards,

Durga Hari

@Abhijith, did this situation ever get resolved?  If yes, what was the solution/change/etc.??