[c-nsp] Nexus 7018 spanning tree and unicast flooding

[Prashanth kumar]

I am trying to troubleshoot a issue with  spanning tree topology change and
unicast flooding during the topology change which I have not seen in 6500.
I am new to nexus series.

+----------+                            +-------------+
|              |                             |                |
| Root     |                             | Secondry |
| SW1     |------------------------| Root        |
|              |------------------------| SW2       |
+----------+                            +------------+
     |                                      /
     |                                 /
     |                             /
     |                 span blocked
+-------------------/---+
|  Access Switch   |
|                            |
+----------------------+

We have a simple topology of two Nexus 7018  aggregation routers in DC and
access-switches connected to two of them as shown above. There are multiple
VLAN's trunked to the access  switches.  All vlans are trunked between Nexus
switch as well.  The Access swtich connection to
second 7018 is blocked.  We run PRSTP+ and all ports on core switch are type
network.  The issue we have is when ever we bring up a new port  or port
state changes on 7018 there is TCN generated and both the switch flush the
cam table and it takes about 15 to 30 second to re-learn the new mac. during
this time we see lot of unicast flooding on all the switches/load balancer
which are connected. Is this a limitation on Nexus 7000 or is this normal
behavior. I have not seen this on 6500.

Thanks you in advance


PK