What happens if an S-Series receives tagged RSTP BPDUs?


Userlevel 7
Hi all,

what happens if an S-Series switch receives tagged a RSTP BPDU on a port?

Standard conforming spanning tree BPDUs are never tagged with a VLAN ID, but some devices add a .1Q tag with VLAN ID to otherwise standard BPDUs (e.g. Alcatel 1x1 mode, or Cisco IOS Rapid-PVST+ combined with tagging the native VLAN), and switches transparently forwarding BPDUs (e.g. because of disabled STP, as done by e.g. EXOS) will add a .1Q tag when a BPDU exits a port where the VLAN it is transported in is tagged.

I have observed the behavior of different switches in this situation, but not yet that of the S-Series:

  • EXOS 15.3 (IIRC) with enabled RSTP will accept the BPDU as if it did not have a tag. I have note checked this with later versions (later EXOS version incorporated quite a few STP changes and additions).
  • Quanta switches with Broadcom FASTPATH SWITCHING software will accept the BPDU as if it did not have a tag.
  • Arista switches will ignore the BPDU, but increment a counter and write a log message.
What does the S-Series with tagged BPDUs?
What do the A-Series, B-Series, C-Series, etc. with tagged BPDUs?
Thanks,
Erik

2 replies

The S-Series, A-Series, B-Series and C-Series will all process the BPDU and don't require a native vlan to be configured.
Userlevel 7
French, Luke wrote:

The S-Series, A-Series, B-Series and C-Series will all process the BPDU and don't require a native vlan to be configured.

Thanks!

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