Switching

Is it necessary to run spanning tree in a metro ethernet network that relies on ERPS for fault tolerance?  It would seem counterproductive to me to run both.

#erps
#stp
#ethernetringprotection
#ethernet

yes, stp has role to play, when any packet resilient protocol like ERPS (G.8032v2) or Foundry's MRP / Huwaei's RRPP / Cisco's REP is already running on the metro ...

these protocol are suitable to provide ring protection over metro-rings in comparison to conventional STP/MSTP/RSTP which is used normal ethernet scenarios ...

regards

Thanks for the response, but I'm still not clear.  If ERPS is used to block ports on a ring, then what purpose does MSTP serve, seeing's how it could take up to a minute to propogate topology changes?

Hi,

 

MSTP does not take a minute to converge, it's based on RSTP(inside MSTP domain) and it's really fast.

If properly engineered it gives really good results.

Regarding your question, ERPS only helps when you have ring topologies but it's not suitable for mesh ones, so in order to be on the safe side you better run both, otherwise you risc a lot as any unexpected loop can bring the whole network down.

To follow on a bit from Dumitru's post - ERPs and others require the topology to be statically configured, generally through e use of a "carrier" VLAN for the ERPs token which is used to form the ring.

MSTP on the other hand caters for dynamic and unexpected topologies (the human factor), because it will converge any topology thrown at it to be loop-free.

There are definitely ways to mitigate against loops in a metro environment so that you no longer need MSTP (shut down non-ring ports, tunnel or filter customer L2 protocols etc), but at the end of the day it comes down to risk.

Cheers,
Ben