VLAN/LAG/VRRP Problem

[clukeman1]

Hello

I have some questions in relation to LAGs, VLANs and VRRP.

1. When adding VLANs to a LAG group, are the VLANs added just to the LAG interface or to the LAG interface and the ports making up the LAG? If the former what is the consequence of also adding them to the port?

2. The LAG is created on two switches S1 and S2, which connect to routers R1 and R2 respectively. The routers use VRRP to provide redundancy and under normal circumstances R1 is the active router.

3. In a recent situation the port configuration including the LAG group was lost on S1. All the data then switched from S1/R1 to S2/R2. The data was put back in the following order

  (a) LAG Group created
  (b) Ports added to LAG group
  (c) VLAN information configured on the ports
  (d) VLAN information configured on the LAG port (3/1).

The ports in the LAG were active (no shutdown) already and the LAG port (3/1) became active when it was created in step a. A switch back to R1/S1 was made before the VLAN data was added back to the LAG (step d). What would have caused the switch back? Trying to find out if configuring the VLANs on the ports caused the problem?

Regards

Chris

[Madhukrishnan Gopinathan Nair]

I hope you are talking about port-channeling by LAG.

If you add the member ports to a port-channel, then ideally all the configuration then needs to be added only to port-channel (LAg) interface. If you are adding vlan to it, do it under LAG interface. If you add vlan under member port and miss to do it under port-channel, i hope it may create problems.

Thanks,

Madhu

[clukeman1]

Thanks Madhu / Devils_advocate

In the situation described above. What would cause R1 to become the active router again. Would it be when the ports are added to the LAG group (step b) or when the VLANs are added to the LAG group (step c)?

Regards

Chris

[Madhukrishnan Gopinathan Nair]

I think when the LAG was created, it would have been allowing all vlans by default and hence depending upon your VRRP preemtion configuration it would have taken the master role,hence you saw the switch back. This is what i can think of.

Hope this helps, and do remember rate all useful posts.

Thanks,

Madhu

[clukeman1]

Thanks Madhu.

The problem we have is that an operation and maintenance link is carried down the LAG. When switch was re-configured we lost the link. I'm just checking that I understand the problem properly. With ports 0/13 and 0/14 up and the port-channel also up we would switch back to R1? I'm assuming at this stage as all the VLANs are enabled by default, that the system will still work, but on R1 (not R2) and that we would not lose our O&M link. The VLAN information was then entered on ports 0/13 and 0/14, but not yet the port-channel. The O&M like other traffic types is in its own VLAN. Was it because we put the VLAN information on 0/13 and 0/14 before the port-channel that caused the link to be lost?

Regards

Chris

[Jon Marshall]

Chris

Not sure what switch you are using but you should configure the allowed vlans on the port channel interface.

The issue is that all ports must have the same configuration to be part of an etherchannel.

If you configure the ports individually then that means once you have configured the first port it now no longer has the same configuration as the second port so it could drop out of the etherchannel.

If you configure the port channel interface then the changes you make should be propagated to the individual ports within the etherchannel.

Jon

[InayathUlla Sharieff]

I agree with John and I always recommend my Customer to follow the following steps while configuring the port-channel to avoid the unpotencial risk.

1- Shutdown the physical interfaces.

2- Create the port-channel and apply all the required infomration on it.

3- Apply the Port-Channel config on the physical ports and then bring the ports back online.

NOte: Once you have created the Port-channel and apply the same to the physical interfaces, Doing the conifg on the interfaces will not have any effect on the PO. But what ever changes/config you do on the port-channel will be inherited by the Interfaces belongs to that PO.

HTH

regards

Inayath

[devils_advocate]

I have always added the ports to the port channel first and then make any future changes to the port channel itself and NOT the individual members.

If you change the port channel (by adding/removing a Vlan), it should update the members automatically.