Oversize Packets Between New and Old Dell Switches Causing Packet Drops

Hello everyone,

I am having a bit of trouble in my network and I was not able to find the root cause. I've been investigating for several weeks, and the only problem I fond are some oversized packets on some LAGs and I am not sure if that is the actual problem.

We recently replaced some old switches (Dell PowerConnect 2848) with new ones (Dell X1052P). Due to inability of configuring the management VLAN on other than VLAN 1 on old switches, we have configured the new ones with the management in the same VLAN 1. We also had to create General ports in between switches to be able to transport the other VLANS as tagged while the management VLAN untagged. 

After the replacement has been done, some strange things started to happen in the network, and I was not able to address or troubleshoot them yet. Other equipments in the management network started to drop packets unexpectedly without changing any configuration on them. I've started to monitor the switches and I saw some oversized packets on some switches (on LAGs connecting new switches with old ones). 

What did I do to troubleshoot so far:

- I've been investigating for layer 2 loops and didn't found any.

- I've checked physical cables or deteriorated switch ports and there aren't any.

- I've checked the configurations multiple times and didn't find anything suspicious or out of common.

 -- Checked the VLANs configurations

 -- Checked the LAGs and ports configurations

- I've checked the CPU on the switches and it runs at about 20-30% load.

- I've checked the logs on the new switches and they don't complain about anything

 

I am not sure if the layer 2 or the switches themselves are responsible for the network behaviour and poor performance, but it all started when we replaced some of the old ones. Beside the oversized packets there are a lot of drops at layer 3. Pinging devices in the same VLAN has a success rate of about 80%, while it use to be 100%.

I've attached a picture of the LAG monitoring of an old switch and a new one. The oversized packets are seen only at the old one end.

X1052PPowerConnect 2848

This is how the interfaces and port-channels are configured:

interface tengigabitethernet1/0/1
channel-group 3 mode on
switchport mode general
switchport general allowed vlan add 2-5,7 tagged
switchport general allowed vlan add 1 untagged
!
interface tengigabitethernet1/0/2
channel-group 3 mode on
switchport mode general
switchport general allowed vlan add 2-5,7 tagged
switchport general allowed vlan add 1 untagged
!
interface tengigabitethernet1/0/3
channel-group 1 mode on
switchport mode general
switchport general allowed vlan add 2-5,7 tagged
switchport general allowed vlan add 1 untagged
!
interface tengigabitethernet1/0/4
channel-group 1 mode on
switchport mode general
switchport general allowed vlan add 2-5,7 tagged
switchport general allowed vlan add 1 untagged
!
interface Port-channel1
flowcontrol on
switchport mode general
switchport general allowed vlan add 2-5,7 tagged
switchport general allowed vlan add 1 untagged
!
interface Port-channel2
flowcontrol on
switchport mode general
switchport general allowed vlan add 2-5,7 tagged
switchport general allowed vlan add 1 untagged
!
interface Port-channel3
flowcontrol on
switchport mode general
switchport general allowed vlan add 2-5,7 tagged
switchport general allowed vlan add 1 untagged
!
interface Port-channel4
flowcontrol on
switchport mode general
switchport general allowed vlan add 2-5,7 tagged
switchport general allowed vlan add 1 untagged
!

 

 

 

The firmware is up to date. I am not sure if there is a mismatch or a compatibility problem between the new switches or the old ones.

I am not sure if the problem was well explained, but hopefully someone can tell me if there is anything wrong?

Thank you!