[Functional] [LAG] | When first interface is deleted from the portchannel with at least two ports, there is a traffic disruption for around 60 seconds

[liorghub]

Description

The issue happens only once per interface. When interface1 is added back to the LAG, after that we can delete and add the same interface1 again without any issues. But, the issue would be seen after removing interface2. After adding it back, the issue would occur again on interface1.

Looks like, the problem is related to the state when the "master" LAG interface is deleted and the traffic is lost for a while.

Setup description:

SW1 and SW2 connected with 2 links

Steps to reproduce the issue:

On SW1 config the following:
config int speed Ethernet32 10000
config int speed Ethernet40 10000
config portchannel add PortChannel0001
config portchannel member add PortChannel0001 Ethernet32
config portchannel member add PortChannel0001 Ethernet40
config interface ip add PortChannel0001 1.0.0.1/24
config interface ip add PortChannel0001 2001::1/64
On SW2 config the following:
config int speed Ethernet72 10000
config int speed Ethernet80 10000
config portchannel add PortChannel0001
config portchannel member add PortChannel0001 Ethernet72
config portchannel member add PortChannel0001 Ethernet80
config interface ip add PortChannel0001 1.0.0.2/24
config interface ip add PortChannel0001 2001::2/64
Send continuous ping from SW2 to SW1 to the IP 1.0.0.1 or 2001::1
While the ping is going, on SW1 delete the interface Ethernet32 (put the correct name accordingly) from the portchannel:
config portchannel member del PortChannel0001 Ethernet32
Check that on SW2 ping stopped sending for around 60 seconds.
On SW1 add the interface Ethernet32 (put the correct name accordingly) back to the portchannel:
config portchannel member add PortChannel0001 Ethernet32
Check that the issue is not reproduced and the traffic is not dropped.
Repeat previous steps 5-8 with interface2.

Describe the results you received:

Traffic is dropped for around 60 seconds

Describe the results you expected:

No traffic loss should be observed when one port is removed from the LAG

Output of show version:

SONiC-OS-202012_9_RC_1.3-23b38b2a7_Internal

Output of show techsupport:

sonic_dump_SW2.tar.gz
sonic_dump_SW1.tar.gz

Additional information you deem important (e.g. issue happens only occasionally):

[saiarcot895]

Can you add a test case for this in sonic-mgmt, or open an issue in sonic-mgmt to add a test case for this?