Comware

I have a couple of Cisco switches that I intend to connect to an existing HPE MST region. The goal is for the HPE switch-already configured with a priority of 0-to remain the root bridge.

The Cisco switches are currently running MST and are interconnected. However, the preference is to integrate all switches (Cisco and HPE) into the same MST region.

There are a few things I'm uncertain about, and I would appreciate your help and guidance:

1. MST Region Compatibility:
   Are there any known interoperability issues between Cisco and HPE switches when both are running MST?
2. Configuration Plan:
   My approach is as follows:

Step 1:
Update the MST configuration on the Cisco switches to match the HPE MST region (same name, revision number, and instance-to-VLAN mappings), leaving the priority at its default.
Question: Will changing the MST region and instance configuration on the Cisco switches cause any traffic disruption or downtime? (Before connecting them to HPE)

Step 2:
Once the MST configuration is confirmed to match, connect the Cisco switches to the HPE switches using trunk links.
Questions:

• Will this connection cause any noticeable downtime or instability during convergence, given that the Cisco switches will need to re-elect the root bridge (now the HPE switch)?
• What is the expected convergence time?
• Will there be any impact on existing traffic within the HPE network? (considering within HPE, the root won't change)
• Is it necessary to configure any BPDU protection on these inter-switch trunk ports? or only configure the port as trunk.
2. VLAN Considerations:
   Only a few VLANs will be required over the trunk links.
   Question: Will configuring the trunks to allow only specific VLANs cause any issues with MST operation? (I understand this differs from VLAN pruning.) i.e between Cisco and HPE I only need layer 2 connectivity for vlan 100 and 200, so I would do trunk allowed vlan 100,200 rather trunk allowed all.

Many thanks

Step 1: Updating Cisco Switches
Question: Will changing the MST region and instance configuration on the Cisco switches cause any traffic disruption or downtime?

Answer: Yes, it will likely cause a brief disruption. When you change the MST configuration (name, revision, and mappings), the Cisco switches will re-elect the root bridge within their existing, isolated MST region and reconverge their spanning tree topology. This process can cause a brief outage or a "flap" in connectivity.

Recommendation: It is best to perform this step during a scheduled maintenance window to mitigate any potential impact on production traffic. The disruption is usually very fast (seconds), but it's a critical configuration change that should not be done live.

Step 2: Connecting the Switches
Question 1: Will this connection cause any noticeable downtime or instability during convergence?

Answer: It should cause minimal to no noticeable downtime. Since your HPE switch has a superior bridge priority (0), the Cisco switches will immediately recognize it as the new root for the entire MST region. The convergence will be quick because the Cisco switches will simply defer to the HPE switch's superior BPDUs and update their root port selections. The change will be a single path update for the Cisco switches, not a full re-computation of the entire spanning tree.

Question 2: What is the expected convergence time?

Answer: The convergence time for MSTP is typically very fast, often sub-second to a few seconds at most. Factors like the number of links and the overall network size can influence this, but in most modern networks, it's a non-issue.

Question 3: Will there be any impact on existing traffic within the HPE network?

Answer: No, there should be no impact on the existing HPE network. Because the HPE switch is already the root bridge with a priority of 0, its own BPDU is the most superior in the topology. The HPE network will not change its root bridge and will simply establish the new trunk links with the Cisco switches. The HPE switches will not need to re-converge their internal topology.

Question 4: Is it necessary to configure any BPDU protection on these inter-switch trunk ports?

Answer: No, absolutely not. You should not configure BPDU protection (e.g., Cisco's BPDU Guard) on ports that connect to other switches. BPDU Guard is intended for access ports connected to end devices to prevent unauthorized switches from being plugged in. Configuring it on a trunk port would cause the port to shut down as soon as it receives a BPDU from the Cisco switch, breaking the connection. The default MSTP behavior on these trunk ports is exactly what you need.

I have a couple of Cisco switches that I intend to connect to an existing HPE MST region. The goal is for the HPE switch-already configured with a priority of 0-to remain the root bridge.

The Cisco switches are currently running MST and are interconnected. However, the preference is to integrate all switches (Cisco and HPE) into the same MST region.

There are a few things I'm uncertain about, and I would appreciate your help and guidance:

1. MST Region Compatibility:
   Are there any known interoperability issues between Cisco and HPE switches when both are running MST?
2. Configuration Plan:
   My approach is as follows:

Step 1:
Update the MST configuration on the Cisco switches to match the HPE MST region (same name, revision number, and instance-to-VLAN mappings), leaving the priority at its default.
Question: Will changing the MST region and instance configuration on the Cisco switches cause any traffic disruption or downtime? (Before connecting them to HPE)

Step 2:
Once the MST configuration is confirmed to match, connect the Cisco switches to the HPE switches using trunk links.
Questions:

• Will this connection cause any noticeable downtime or instability during convergence, given that the Cisco switches will need to re-elect the root bridge (now the HPE switch)?
• What is the expected convergence time?
• Will there be any impact on existing traffic within the HPE network? (considering within HPE, the root won't change)
• Is it necessary to configure any BPDU protection on these inter-switch trunk ports? or only configure the port as trunk.
2. VLAN Considerations:
   Only a few VLANs will be required over the trunk links.
   Question: Will configuring the trunks to allow only specific VLANs cause any issues with MST operation? (I understand this differs from VLAN pruning.) i.e between Cisco and HPE I only need layer 2 connectivity for vlan 100 and 200, so I would do trunk allowed vlan 100,200 rather trunk allowed all.

Many thanks

Thanks for the explanation. more confident now about what I'm doing

Step 1: Updating Cisco Switches
Question: Will changing the MST region and instance configuration on the Cisco switches cause any traffic disruption or downtime?

Answer: Yes, it will likely cause a brief disruption. When you change the MST configuration (name, revision, and mappings), the Cisco switches will re-elect the root bridge within their existing, isolated MST region and reconverge their spanning tree topology. This process can cause a brief outage or a "flap" in connectivity.

Recommendation: It is best to perform this step during a scheduled maintenance window to mitigate any potential impact on production traffic. The disruption is usually very fast (seconds), but it's a critical configuration change that should not be done live.

Step 2: Connecting the Switches
Question 1: Will this connection cause any noticeable downtime or instability during convergence?

Answer: It should cause minimal to no noticeable downtime. Since your HPE switch has a superior bridge priority (0), the Cisco switches will immediately recognize it as the new root for the entire MST region. The convergence will be quick because the Cisco switches will simply defer to the HPE switch's superior BPDUs and update their root port selections. The change will be a single path update for the Cisco switches, not a full re-computation of the entire spanning tree.

Question 2: What is the expected convergence time?

Answer: The convergence time for MSTP is typically very fast, often sub-second to a few seconds at most. Factors like the number of links and the overall network size can influence this, but in most modern networks, it's a non-issue.

Question 3: Will there be any impact on existing traffic within the HPE network?

Answer: No, there should be no impact on the existing HPE network. Because the HPE switch is already the root bridge with a priority of 0, its own BPDU is the most superior in the topology. The HPE network will not change its root bridge and will simply establish the new trunk links with the Cisco switches. The HPE switches will not need to re-converge their internal topology.

Question 4: Is it necessary to configure any BPDU protection on these inter-switch trunk ports?

Answer: No, absolutely not. You should not configure BPDU protection (e.g., Cisco's BPDU Guard) on ports that connect to other switches. BPDU Guard is intended for access ports connected to end devices to prevent unauthorized switches from being plugged in. Configuring it on a trunk port would cause the port to shut down as soon as it receives a BPDU from the Cisco switch, breaking the connection. The default MSTP behavior on these trunk ports is exactly what you need.

I have a couple of Cisco switches that I intend to connect to an existing HPE MST region. The goal is for the HPE switch-already configured with a priority of 0-to remain the root bridge.

The Cisco switches are currently running MST and are interconnected. However, the preference is to integrate all switches (Cisco and HPE) into the same MST region.

There are a few things I'm uncertain about, and I would appreciate your help and guidance:

1. MST Region Compatibility:
   Are there any known interoperability issues between Cisco and HPE switches when both are running MST?
2. Configuration Plan:
   My approach is as follows:

Step 1:
Update the MST configuration on the Cisco switches to match the HPE MST region (same name, revision number, and instance-to-VLAN mappings), leaving the priority at its default.
Question: Will changing the MST region and instance configuration on the Cisco switches cause any traffic disruption or downtime? (Before connecting them to HPE)

Step 2:
Once the MST configuration is confirmed to match, connect the Cisco switches to the HPE switches using trunk links.
Questions:

• Will this connection cause any noticeable downtime or instability during convergence, given that the Cisco switches will need to re-elect the root bridge (now the HPE switch)?
• What is the expected convergence time?
• Will there be any impact on existing traffic within the HPE network? (considering within HPE, the root won't change)
• Is it necessary to configure any BPDU protection on these inter-switch trunk ports? or only configure the port as trunk.
2. VLAN Considerations:
   Only a few VLANs will be required over the trunk links.
   Question: Will configuring the trunks to allow only specific VLANs cause any issues with MST operation? (I understand this differs from VLAN pruning.) i.e between Cisco and HPE I only need layer 2 connectivity for vlan 100 and 200, so I would do trunk allowed vlan 100,200 rather trunk allowed all.

Many thanks