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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.
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).
10 Replies
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- 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).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.
- 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
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