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Re: LAG ports create DUP packets and STP chaos

cw_tec
Guide

LAG ports create DUP packets and STP chaos

Hi @all.

 

We have exchanged or previous Aruba switches with Netgear XSM4348S switches, which are acting as a stack (4 switches). Behind these switches are GSM4328S & GS728TPPv2, which are connected by LAGs for VLAN passthrough and bandwith.

 

The setup:

 

4x XSM4348S (stacked)

2x GSM4328S

4x GS728TPPv2

 

STP (RSPT) is enabled on each switch, the stack acts as STP master (priority 4096), all other switches have higher STP values (lower priority).

 

On the stack 2 ports on one switch are created as LAG1, another 2 ports as LAG2 on the fourth switch (standard hash mode type 2). LAG1 is connected to both SFP ports of the first GSM4328S, LAG2 to both SFP ports on the second GSM4328S.

 

Each GSM4328S has three LAGs:

 

- 1x2 port LAG1 for uplink to the stack

- 2x1 port LAG2 and LAG3 for connections to the GS728TPPv2

 

I attached a schematic picture of our setup.

 

The problems:

 

- the "uplink" LAG ports between the stack and each GSM4328S create DUP packets, VLAN packets are not transmitted

- the GS728TPPv2 switches behind the GSM4328S are constantly detecting STP changes which results in port flapping (port is closed due to STP bridge topology changes)

 

As soon as one of the 2 port LAG fibre cables is pulled everything runs normal. We already tried different STP and LAG hash modes with no positive effect.

 

Funny thing: we didn't have these problems with a nearly identical setup of our Aruba switches in "front" of the GSM4328S.

 

 

 

 

 

 

 

Model: XSM4348S|M4300-24X24F - Stackable Managed Switch with 48x10G including 24x10GBASE-T and 24xSFP+ Layer 3
Message 1 of 11

Accepted Solutions
cw_tec
Guide

Re: LAG ports create DUP packets and STP chaos

Today I gave it another try - long story short:

 

not the stack switch was the problem but the M4300s behind it. AFAIK all M4300 don't use the static mode by default which means that LACP is used. I had to reset the M4300 to factory defaults (but not the stack) and start over. After I reconfigured the M4300s which are connected behind the stack by re-importing the config the LAG came up as usual and works.

 

Side notice: when using a standard LAG in the M4300 series in combination with the mentioned Smart Managed switches (GS728TPPv2) you have to set the LACP mode on the GS728TPPv2 manually. Unlike the M4300s the Smart Managed switches seem to use the static mode by default. Same applies to other vendors like HP (ProCurve series).

 

 

 

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Message 11 of 11

All Replies
schumaku
Guru

Re: LAG ports create DUP packets and STP chaos

Reads like we have some basic definition problem: A one-port LAG - what is the point of this? Are you probably mix up the functionality of a LAG (port aggregation) with a port or a LAG configured as a trunk for handling multiple VLAN?

Different hash modes are only defining on how the traffic is distributed on a LAG with multiple physical !inks.

If STP issues arise on LAGs, it's an indication that the LAG are not set-up correct, the duplicate packets confirm this.

Another possibility is that you mix stack ports (which automatically handle all VLAN between stack members) with LAG - an impossible config.

I would strongly suggest to configure all M4300s in a stack, with all links in stack port mode. The links to the Smart Managed switches must be configured as trunk, all VLANs tagged, probably except of one VLAN which can be operated untagged and that same PVID, on general Ethernet (not stack mode).
Message 2 of 11
cw_tec
Guide

Re: LAG ports create DUP packets and STP chaos

Thank you for your answer.

 

Reads like we have some basic definition problem: A one-port LAG - what is the point of this? Are you probably mix up the functionality of a LAG (port aggregation) with a port or a LAG configured as a trunk for handling multiple VLAN?

 

Maybe I'm blind but I don't find any other possibilty to set up a singe trunk port but using the LAG feature in the web interface. All LAGs which are created with single or multiple ports are automatically defined as trunk (port type).

 

Another possibility is that you mix stack ports (which automatically handle all VLAN between stack members) with LAG - an impossible config.

 

I'm absolutely sure that this is not the case. Checked more than twice.

 

I would strongly suggest to configure all M4300s in a stack, with all links in stack port mode.

 

Is this the "official" way to connect switches of the same series? What if you have (for example) 12 or more of these switches? Is it really advisable to configure them all in one big stack?

 

The links to the Smart Managed switches must be configured as trunk, all VLANs tagged, probably except of one VLAN which can be operated untagged and that same PVID, on general Ethernet (not stack mode).

 

That's the reason why I configured them as LAGs and not stack ports, even if they are only connected with on SFP port.

Message 3 of 11
schumaku
Guru

Re: LAG ports create DUP packets and STP chaos

In general, Netgear does differentiate the port or LAG usage based on theport or LAG VLAN config.

https://kb.netgear.com/11673/How-do-I-setup-a-VLAN-trunk-link-between-two-NETGEAR-switches

The simple availability for define access resp trunk port became available on the M4240/4300 models, too.

The question on the number of switches in a distributed stack I'd prefer to call in @LaurentMa
Message 4 of 11
cw_tec
Guide

Re: LAG ports create DUP packets and STP chaos

Thanks.

I can reconfigure the single LAG ports to the GS728TPPv2 back to normal ports and tag the uplink connections, but that doesn’t explain why the connections from the stack switch with 2 ports in each LAG don’t work.
Message 5 of 11
schumaku
Guru

Re: LAG ports create DUP packets and STP chaos

The same tagging is required on the LAGs.

Again: LAGs are just for bonding bandwidth. Anything else must be configured individually again, being VLAN by VLAN tagged (or define the LAG as a trunk where available).
Message 6 of 11
cw_tec
Guide

Re: LAG ports create DUP packets and STP chaos

Thanks again, I appreciate your help.

But the primary problem ist still the packet duplicating and disfunctional LAG with 2 ports on each switch. I tried it with only one additional M4300 connected by LAG to the stack but the error remains, even with no VLANs defined (just the default VLAN).
Message 7 of 11
schumaku
Guru

Re: LAG ports create DUP packets and STP chaos

Managed to discover what was wrong on this configuration in the meantime?
Message 8 of 11
cw_tec
Guide

Re: LAG ports create DUP packets and STP chaos

No, I have no clue what's wrong.

 

Every time I create a LAG and connect it later to another LAG it creates a loop.

 

Example:

 

- on the stack switch I create a LAG on port 1/0/10 and 1/0/11

- on another M4300 I create a LAG on port 1/10 and 1/11

- disconnect the other M4300 from the network which is "behind" the stack, plugin both fibre cables into port 1/10 and 1/11, the same on the stack switch on port 1/0/10 and 1/0/11

- as soon as the ports are connected I have a loop and port flapping (constant topology changes in STP)

 

[ STACK SWITCH ] <-- single port connection --> [ M4300 ] works

[ STACK SWITCH ] <== dual port (LAG) connection ==> [ M4300 ] loop

 

What's really strange is that as soon as the single M4300 (or another NETGEAR switch like the GS728TPPv2) is connected on the LAG ports the stack switch marks the LAG as down. In addition the loop detection on the stack switch(es) and on other NETGEAR switches behind shows 0 loop counts although loop protection is enabled. Only the firewall and Wireshark show the DUP packets. Or (for quick and simple testing) I plugged in another tiny GS108T switch with one port into the stack or the M4300 which is behind and it immediately shuts down the uplink port with a log entry of a detected loop.

 

The only thing I could try is to completely reset each of the four stack switches to factory defaults and start over again from zero.

 

Btw.: it's not the first time I created a stack or LAG with NETGEAR switches. Never saw that before.

 

 

 

Message 9 of 11
schumaku
Guru

Re: LAG ports create DUP packets and STP chaos

The LAG show down if the mode (LACP) isn't configured on both ends, or the the wrong links are assigned (or plugged) for the LAG. If another switch in the same LAG does proof, figure - a loop is predictable. Nothing you don't know already of course.

Netgear Support should be able to help, not sur fellow @LaurentMa is able to join in or offer the Pro AV support email channel here.
Message 10 of 11
cw_tec
Guide

Re: LAG ports create DUP packets and STP chaos

Today I gave it another try - long story short:

 

not the stack switch was the problem but the M4300s behind it. AFAIK all M4300 don't use the static mode by default which means that LACP is used. I had to reset the M4300 to factory defaults (but not the stack) and start over. After I reconfigured the M4300s which are connected behind the stack by re-importing the config the LAG came up as usual and works.

 

Side notice: when using a standard LAG in the M4300 series in combination with the mentioned Smart Managed switches (GS728TPPv2) you have to set the LACP mode on the GS728TPPv2 manually. Unlike the M4300s the Smart Managed switches seem to use the static mode by default. Same applies to other vendors like HP (ProCurve series).

 

 

 

Message 11 of 11
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