Summary

The STP module validates the global stp.protocol setting against device capabilities, but does not validate node-level protocol overrides. This allows users to configure unsupported STP protocols on individual nodes without receiving an error.

Environment

• netlab version: Current (as of branch fix_minor_stp_issues)
• Module: stp
• Affected devices: All devices with STP support

Description

When a user sets stp.protocol at the node level (e.g., nodes.s1.stp.protocol: mstp), the STP module does not validate whether the device supports that protocol. The module only validates the global stp.protocol setting.

Current Code Behavior

In netsim/modules/stp.py, lines 41-47:

protocol = topology.get("stp.protocol","stp")
supported_protocols = features.get("stp.supported_protocols",[])
if protocol not in supported_protocols:
    log.error(
        f'node {node.name} (device {node.device}) does not support requested STP protocol ({protocol})',
        log.IncorrectValue,
        'stp')

This only checks the global protocol, not node-level overrides.

Steps to Reproduce

1. Create a topology with a device that has limited STP protocol support (e.g., FRR which only supports stp)
2. Set a node-level protocol override to an unsupported protocol (e.g., mstp)
3. Run netlab create on the topology

Minimal Test Topology

---
defaults:
  device: frr

stp:
  protocol: stp  # Global default

addressing:
  p2p:
    ipv4: False  # STP only applies to L2 interfaces

groups:
  _auto_create: true
  switches:
    members: [s1, s2]
    module: [vlan, stp]

vlans:
  red:
    mode: bridge
    links: [s1-s2]

links:
- s1:
  s2:

nodes:
  s1:
    # Node-level protocol override - should be validated but currently isn't
    stp.protocol: mstp  # FRR doesn't support MSTP, should error

File location: tests/ai/stp-validation-issues.yml

Expected Behavior

When running netlab create on the above topology, it should produce an error:

IncorrectValue in stp: node s1 (device frr) does not support requested STP protocol (mstp)

Actual Behavior

The topology is created successfully without any validation errors, even though:

• FRR device only supports stp protocol (see netsim/devices/frr.yml line 138: supported_protocols: [ stp ])
• Node s1 is configured with stp.protocol: mstp which is not supported

Impact

• Severity: Medium
• Impact: Users can configure invalid STP protocols on nodes, leading to:
  • Configuration generation that may not work as expected
  • Runtime errors when the lab is started
  • Confusion about why certain configurations don't work

Suggested Fix

The validation should check node-level protocol overrides in addition to the global protocol. Suggested code change in netsim/modules/stp.py:

# Check global protocol
protocol = topology.get("stp.protocol","stp")
supported_protocols = features.get("stp.supported_protocols",[])
if protocol not in supported_protocols:
    log.error(
        f'node {node.name} (device {node.device}) does not support requested STP protocol ({protocol})',
        log.IncorrectValue,
        'stp')

# Check node-level protocol override
node_protocol = node.get('stp.protocol', protocol)
if node_protocol not in supported_protocols:
    log.error(
        f'node {node.name} (device {node.device}) does not support requested STP protocol ({node_protocol})',
        log.IncorrectValue,
        'stp')

Additional Context

• The global protocol validation works correctly
• Node-level priority validation works correctly (validates multiples of 4096)
• This is a missing validation check, not a logic error
• Related issue: The protocol attribute in stp.yml node section is missing a definition (should have copy: global or explicit type)

References

• STP module: netsim/modules/stp.py
• STP defaults: netsim/modules/stp.yml
• FRR device features: netsim/devices/frr.yml (line 138)
• Test topology: tests/ai/stp-validation-issues.yml