[c-nsp] MST and Uplinkfast

[Andy Saykao]

Hi All,

I have noticed that with MST and rapid failover that those ports which
are not boundary ports or do not have portfast enabled go through the
blocking, listening and learning states again before forwarding.

Here's me shutting off the primary link Gi0/49. You can see the
redundant link on Gi0/51 goes straight into forwarding but those ports
which are not boundary ports or do not have portfast enabled go through
their various states again.

Interface        Role Sts Cost      Prio.Nbr Type
---------------- ---- --- --------- --------
--------------------------------
Gi0/1            Desg BLK 2000000   128.1    P2p
Gi0/2            Desg FWD 2000000   128.2    P2p Bound(STP)
Gi0/3            Desg FWD 200000    128.3    P2p Bound(STP)
Gi0/4            Desg BLK 200000    128.4    P2p
Gi0/51           Root FWD 40000     128.51   P2p

Interface        Role Sts Cost      Prio.Nbr Type
---------------- ---- --- --------- --------
--------------------------------
Gi0/1            Desg LRN 2000000   128.1    P2p
Gi0/2            Desg FWD 2000000   128.2    P2p Bound(STP)
Gi0/3            Desg FWD 200000    128.3    P2p Bound(STP)
Gi0/4            Desg LRN 200000    128.4    P2p
Gi0/51           Root FWD 40000     128.51   P2p

Interface        Role Sts Cost      Prio.Nbr Type
---------------- ---- --- --------- --------
--------------------------------
Gi0/1            Desg FWD 2000000   128.1    P2p
Gi0/2            Desg FWD 2000000   128.2    P2p Bound(STP)
Gi0/3            Desg FWD 200000    128.3    P2p Bound(STP)
Gi0/4            Desg FWD 200000    128.4    P2p
Gi0/51           Root FWD 40000     128.51   P2p

When I bring the primary link back up, those same ports go through their
blocking, listening and learning states again.

Interface        Role Sts Cost      Prio.Nbr Type
---------------- ---- --- --------- --------
--------------------------------
Gi0/1            Desg BLK 2000000   128.1    P2p
Gi0/2            Desg FWD 2000000   128.2    P2p Bound(STP)
Gi0/3            Desg FWD 200000    128.3    P2p Bound(STP)
Gi0/4            Desg BLK 200000    128.4    P2p
Gi0/49           Root FWD 20000     128.49   P2p
Gi0/51           Altn BLK 40000     128.51   P2p

Interface        Role Sts Cost      Prio.Nbr Type
---------------- ---- --- --------- --------
--------------------------------
Gi0/1            Desg LRN 2000000   128.1    P2p
Gi0/2            Desg FWD 2000000   128.2    P2p Bound(STP)
Gi0/3            Desg FWD 200000    128.3    P2p Bound(STP)
Gi0/4            Desg LRN 200000    128.4    P2p
Gi0/49           Root FWD 20000     128.49   P2p
Gi0/51           Altn BLK 40000     128.51   P2p

Interface        Role Sts Cost      Prio.Nbr Type
---------------- ---- --- --------- --------
--------------------------------
Gi0/1            Desg FWD 2000000   128.1    P2p
Gi0/2            Desg FWD 2000000   128.2    P2p Bound(STP)
Gi0/3            Desg FWD 200000    128.3    P2p Bound(STP)
Gi0/4            Desg FWD 200000    128.4    P2p
Gi0/49           Root FWD 20000     128.49   P2p
Gi0/51           Altn BLK 40000     128.51   P2p

I guess what I'll take out of this with MST is that I should enable
portfast on those ports where we have devices that can not tolerate a
fail over of 20-30secs as the port needs to go through it's spanning
tree states whenever a fail over occurs and does the same thing again
when the primary link is restored.

Cheers.

Andy


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