Ethernet Switches & Routers

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Occasional Contributor
Posts: 9
Registered: ‎05-26-2011

Interface state incorrect - cosmetic

This isn't necessarily a problem, but interesting nonetheless.

 

To hopefully make things simple, I have a triangle of switch connections - 3 switches connected together to form a triangle.  Each link is a different vlan number. 

 

Switch A connects to switch B with vlan 10

Switch B connects to switch C with vlan 11

Switch C connects to switch A with vlan 12

 

All links are up, no spanning tree blocks, traffic passes through all links as necessary.

 

Now, I add a vlan that's common to all switches (vlan 20) and add it to all three interconnecting links.  Spanning tree blocks on one interface in the triangle to prevent a loop.  This is expected and correct.

 

The point of this post is that the port where spanning tree does the blocking, the port state shows "Blocked" in the interface status even though it's only blocked on one vlan and not the other.

 

Below is what it actually looks like on my live switch.  As you can see, it's blocking the common vlan, but not the vlan that's not looped, however the interface status shows "blocked".

 

There's no problem here, but the interface status is weird.  Yes, it's blocking, but not entirely.  Perhaps I'm being overly sensitive to this cosmetic thing. I was expecting it to say "Foward" still.  Perhaps there should be another port status, "Fwd/Blk"?

 

 

--- VLAN 10 [ STP Instance owned by VLAN 10 ] ----------------------------
Port      Pri PortPath P2P Edge Role       State       Designa-  Designated
Num           Cost     Mac Port                        ted cost  bridge
1/1/2     128 2000     T   F    ALTERNATE  DISCARDING  2000      0001609c9fd73700

 

--- VLAN 20 [ STP Instance owned by VLAN 20 ] ---------------------------
Port      Pri PortPath P2P Edge Role       State       Designa-  Designated
Num           Cost     Mac Port                        ted cost  bridge
1/1/2     128 2000     T   F    ROOT       FORWARDING  0         0000609c9fd73700

 

 

#sh int br e 1/1/2

Port       Link    State   Dupl Speed Trunk Tag Pvid Pri MAC             Name
1/1/2      Up      Blocked Full 10G   3     Yes 1    0   609c.9f21.1700  switch

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