Use of REP in a large spanning tree domain

[dstehle]

A question concerning the use of REP for IE-3000-4TC  switches:

In figure 14 of REP pdf (see http://www.cisco.com/en/US/prod/collateral/switches/ps6568/ps6580/prod_white_paper0900aecd806ec6fa.pdf), can you explain why this  creates a loop in the system? From the document, I thought REP and RSTP could  talk to each other so why does this create a loop if they are exchanging  information between each other? Also, if, in figure 14, the two switches in the  STP domain that connect to the REP ring, were also connected to each other,  would there still be a loop in the system?

Also, what is the recommended max diameter a REP ring should be. I thought I read some  place 130 nodes is ok, but I'm looking to confirm this.

Thanks,

David

[Matthew Blanshard]

Hello David,

There is TCN propagation between rep and RSTP but REP and RSTP don't directly interact with each other.  So in figure 14 RSTP has no knowledge of the REP link between the two switches so it doesn't block any ports.  You would need a link between the two switches running RSTP to offset that and cause blocking in the proper place. Also we have customer using upwards of 100+ nodes in rep rings with no issues.  The more switches the longer it takes to converge after a link failure.  Even with 100 switches though the convergence time is much less than RSTP.

-Matt

[dstehle]

Thanks again Matt!

[coletemple]

Dear all,

I am new in REP and my company is planning to have a ring with ME3800 Switches connected together to form a ring. This ring will be an access ring for my customers. At the edge switch, we have connected one port of the edge swith (port not in the rep segment) to our core switch (which is a normal Cisco 3560 Switch) through a normal STP trunk.

When i connect the ring to the 3560 Switch (to connect the ring to the core, using a trunk port), i see the port where it is connected blinks very fast which leads me to think that it may be a loop.

I have put my design in the attached file and hope you'll help me to understand.

Regards,

[valichibadoo]

This is just a suggestion:

Configuration at  HQ Edge Swith

int g1/0/1
switchport trunk encapsulation dot1q
switchport mode trunk
switchport trunk allowed vlan 1,2,3,etc
switchport trunk native vlan 3
rep segment 1 edge primary

rep block port 4 vlan n-1

rep stcn sement 2

int g1/0/2
switchport trunk encapsulation dot1q
switchport mode trunk
switchport trunk allowed vlan 1,2,3,etc
switchport trunk native vlan 3
rep segment 1 edge secondary

int g1/0/3
switchport trunk encapsulation dot1q
switchport mode trunk
switchport trunk allowed vlan 1,2,3,etc
switchport trunk native vlan 3
rep segment 2 edge no-neighbor

rep stcn stp
rep preempt delay 30

Configuration at L2 Switch

int g1/0/4
switchport trunk encapsulation dot1q
switchport mode trunk
switchport trunk allowed vlan 1,2,3,etc
switchport trunk native vlan 3

I hope this help. just fine tune it to suit your network