BackboneFast/Rapid STP

ns · ‎05-05-2003

Hi,

What implications can activating BackboneFast/RSTP have on switches in a production environment?

The thing is I have to lower the convergence time of STP.

The connection topology is the following:

A ->B->C->D->A

A and B are core/distribution connected via a FastEther Channel (all other conections are gigabit), switches and C, D are access switches.

A,B are 6509 switches running CatOS 5.4 and C, D are 2950G-EI running IOS 12.1(12c).

I have configured VLAN 801 which has switch C as root and secondary root is switch D. Switch B has blocked the connection to switch A on this VLAN.

If I disconnect the Gbit interface between C and D there is a looong delay, of course, when STP is converging and I believe that BackboneFast or RSTP can lower this convergence delay, but which one is the better option?

Cheers,

Niels

ivillegas · ‎05-09-2003

Backbone fast is a feature that enables a switch to detect an indirect link failure and save STP approximately 20s in recovergence time. Backbone fast should be enabled on all switches.

Here are possible STP parameters for network with diameter 10, but it is not recommended to tune it

at all because your convergence time will increase or

if you set hello to 1 sec, it will have implications like higher CPU utilization of the switches and

of course you must be sure that your network througput will allow it

hello : 2 sec

Fw Delay: 19 sec

Max age: 26 sec

or

hello = 1 sec

Fw dDelay : 17 sec

Max age : 22 sec

RSTP have max. default hop count 20, can be changed to 40

I think in your case you can go for RSTP also refer the link

http://www.cisco.com/univercd/cc/td/doc/product/lan/cat2950/12111ea1/scg/swmstp.htm#1008347