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OS10 default STP protocol
OS10 defaults to "Spanning tree enabled protocol rapid-pvst with force-version rstp". Does this mean that when it interacts with Cisco switches it uses Rapid-PVST+ but when it interacts with other manufacturer switches, it just uses RSTP?
Thanks.
DELL-Charles R
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March 5th, 2024 16:28
Joey’s suggestion was to change the spanning-tree version on the Dell switch to rstp, which is commonly done because rstp is simpler.
(config)#spanning-tree mode rstp
Your initial question was about the default spanning-tree mode for OS10 rapid-pvst.
(config)# spanning-tree mode rapid-pvst
When there is no “force-version” configured, compatibility-mode is the default rstp.
You can see that by using command “# show spanning-tree compatibility-mode”
The default spanning-tree version on OS10 is rapid-pvst. Rapid-pvst creates a separate spanning-tree topology per vlan, so interfaces can be placed in different vlans (via configuration). Because it is “rapid” it provides faster convergence timers. When compatibility-mode is rstp (which is the default compatibility mode), even though there are several spanning tree instances (per vlan) on the switch, when sending out BPDUs, BPDUs are not sent out in all these different vlans, instead BPDUs are sent out only in the untagged vlan on the trunk to other switches. By default, OS10 sends RSTP BPDU in the untagged VLAN.
The Dell switch is not distinguishing whether there is a Cisco switch or another manufacturer switch or another Dell switch on the other side of the link. The switches just send and receive these BPDU messages to agree on a compatible version.
DELL-Joey C
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March 1st, 2024 07:04
Hi,
It can interact with Cisco switches, using RPVST+. If you were to have need to use RSTP, you will need to change the configuration, #spanning-tree mode rstp
DB_2022
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March 1st, 2024 14:45
Thanks for the reply.
If that's the case, what does "force-version rstp" mean?
DELL-Erman O
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March 1st, 2024 15:31
Hi, The
force-version rstpcommand in the context of Spanning Tree Protocol (STP) is used to set the spanning tree compatibility mode. This command forces the switch to emulate the behavior of earlier versions of the spanning tree protocol.you can take a look RSTP (Dell EMC) and RPVST+ (Cisco) | Dell EMC Spanning Tree Interoperability Reference Guide | Dell Technologies Info Hub
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March 1st, 2024 16:20
So if a switch is left at default (Rapid-PVST with force-version RSTP) which protocol is it going to use with Cisco switches running Rapid-PVST?
Alternatively, which protocol is it going to use with a non-Cisco switch running RSTP?
DELL-Charles R
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March 1st, 2024 18:48
Hello,
By default, Dell Networking OS10 switches are configured to use Rapid-PVST with the "force-version rstp" option. This configuration allows the OS10 switch to communicate with both Cisco switches running Rapid-PVST and non-Cisco switches running RSTP. The "force-version rstp" option ensures compatibility with non-Cisco switches by using the RSTP protocol when communicating with them.
So if a Dell Networking OS10 switch is left at its default configuration, it will use Rapid-PVST with the "force-version rstp" option, allowing it to interoperate with both Cisco switches running Rapid-PVST and non-Cisco switches running RSTP.
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March 5th, 2024 14:29
Thanks for the reply. So, just to be clear, the reply from your colleague Joey-C was incorrect, yes? You don't have to set the switch to use RSTP manually, it will use it by default if it encounters a non-Cisco switch. Have I understood that correctly?
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March 15th, 2024 18:57
Thanks for the explanation.