[f-nsp] Spanning-tree event on single VLAN brings down LAG?

[Howard, Christopher]

One vlan getting blocked by spanning tree should not bring down the lag. The vlan should only block on the interfaces required to remove the loop. As far as I know, if you have spanning tree enabled on the vlan, but disabled on the physical port, then the physical port no longer participates in spanning tree for any vlan.


Here's config from one of my switches. This is an ICX7750 with 8.0.30r code, same code that ICX6610 can run.


lag lag-name dynamic id 1

 ports ethernet 1/1/2 ethernet 2/1/2

 primary-port 1/1/2

 deploy

!

vlan 123 name vlan-name by port

 tagged ethe 1/1/2 ethe 2/1/2

 spanning-tree 802-1w

!

interface ethernet 1/1/2

 spanning-tree 802-1w admin-pt2pt-mac


A snipped output from "show 802-1w" below with vlans in both discarding and forwarding states on that lag.

--- VLAN 404 [ STP Instance owned by VLAN 404 ] ----------------------------
1/1/2     128 2000     T   F    ALTERNATE  DISCARDING  2000      0001609c9fd73700

--- VLAN 999 [ STP Instance owned by VLAN 999 ] ----------------------------
1/1/2     128 2000     T   F    ALTERNATE  DISCARDING  2000      0001609c9fd73700

--- VLAN 2007 [ STP Instance owned by VLAN 2007 ] ---------------------------
1/1/2     128 2000     T   F    ROOT       FORWARDING  0         0000609c9fd73700

--- VLAN 2057 [ STP Instance owned by VLAN 2057 ] ---------------------------
1/1/2     128 2000     T   F    ROOT       FORWARDING  0         0000609c9fd73700

-Christopher


On Wed, 2018-10-10 at 11:59 -0500, Frank Bulk wrote:

We had network event deeper in our network that resulted in some kind of

spanning tree event as evidenced by a TC (topology change) on our L2-only

ICX6610 stack.  What surprised us was that one VLAN going into a blocking

state resulted in the south bound LAG going down.


This is probably not right, but the root bridge for VLAN 294 is on the

ICX6610 stack. VLAN 294 is on both LAGs (and no other port/LAG)


Three questions:

a) when a STP event occurs is it normal that a VLAN goes into Blocking on

all the ports where it is present?

b) when a VLAN goes into blocking should all the physical (or LAG) ports

associated with that VLAN go down?

c) does configuring spanning tree on the port-based VLAN but disabling

spanning-tree on the physical (or LAG) ports prevent the physical port (or

LAG) going down?


Frank


============================================================================

====

Oct  9 21:35:22 STP: VLAN 294 Port 1/3/6 Bridge TC Event (MakeBlking)

Oct  9 21:35:22 STP: VLAN 294 Port 1/3/6 STP State -> BLOCKING (MakeBlking)

Oct  9 21:35:25 System: Logical link on dynamic lag interface ethernet 2/3/8

is down.

Oct  9 21:35:25 System: Logical link on dynamic lag interface ethernet 3/3/4

is down.

Oct  9 21:35:26 System: Logical link on dynamic lag interface ethernet 3/3/8

is down.

Oct  9 21:35:29 Trunk: Group (1/3/8, 2/3/8, 3/3/4, 3/3/8) removed by 802.3ad

link-aggregation module.

Oct  9 21:35:29 STP: VLAN 4 Port 1/3/8 STP State -> BLOCKING (PortDown)

Oct  9 21:35:29 STP: VLAN 4 Port 1/3/8 STP State -> DISABLED (PortDown)

etc.


 Event

   |

Transport

  | |

  | |   (1/3/6 & 2/3/6)

  | |

ICX6610 (L2)

 | | | |

 | | | | (1/3/8, 2/3/8, 3/3/4, 3/3/8)

 | | | |

Core (L3)





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