Saturday, September 15, 2018

Oversize Packets on a Dell 3000 series

Hi guys, hoping somebody could shed some light on this for me.

I have a stack of 7 dell N3000 series that i use mainly for my clients, but also for some servers. Seperated into VLAN's.

I have a connection from this stack on tengigabitethernet to another stack of 2 M6348 in the back of a blade chassis.

Historically, i would have all my servers on VLAN 10 on the N3000 stack, on the M6348's i only have servers, so i set all untagged traffic to VLAN 10. Communication between these were fine.

However i have tried to kind of up my security a bit, and i have segregated my servers out in to more VLAN's this has included 3 new VLANS; 12, 14 and 16 I started moving one blade at a time to this configuration, currently i have 3 set up like this with communication back between the old 10 VLAN without issue (or so i thought). I moved 2 servers in a hyper-v file server cluster to 2 of the blades and the following day my users started reporting that applications that rely on these servers etc were crashing. Upon inspection i noticed millions of Oversize Packets on the M6348's.

I configured MTU to 9216 across the stack and thought that would be it sorted, however the problems persisted and i found more oversize packets being reported on the tengigabitethernet port connected to the M6348 from the N3000 stack. So i configured 9216 MTU across the stack as well, rebooted the switches. However the Oversize Packets keep appearing on the N3000 size. The port shows an MTU of 9216.

I am not a network guy, but trying to do my best. I have ran pings from servers not in the new setup to servers in the new setup and i cant see any packets being dropped. I was wondering if it was the configuration of the new VLANs within the servers themselves, I used MS VMM to build logical switches etc. But i am kind of at a loss on how to troubleshoot this issue further.

Any advice is greatly appreciated!



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