30 seconds interruption upon link recovery

[dhcchan]

Hi there,

I got a pair of Cat 4506 which interconnect with a pair of GBIC. Also, I got a pair of Cat 3550XL-SMI which interconnect with Cat 3500 G-Stack. There is one fiber connection between between a Cat 3550XL-SMI and a Cat 4506. When I perform a failover test on the G-Stack cable, the interruption upon the G-Stack fail is very too time, talking about 1 or 2 second. However, when I re-connect the G-Stack, there is a interruption talking about 30 second. I have configured those swtiches traditional spanning tree with backbone fast, uplinkfast and stack-port enable. May I ask that is there any way to minimize the interruption upon the re-connection of G-Stack cable?

many thanks

David

[konigl]

This sounds like Spanning Tree sorting itself out again. All you can really do under STP is minimize the timers.

To minimize Max Age (MA) and Forwarding Delay (FD), adjust your Hello Time (HT) down to 1 second and figure out what your L2 Network Diameter (ND) is, per VLAN. Then, plug these values into the formulas in this post, rounding up if appropriate, and calculate optimum MA and FD for each VLAN.

http://forum.cisco.com/eforum/servlet/NetProf?page=netprof&CommCmd=MB%3Fcmd%3Ddisplay_location%26location%3D.ee9e70c

HT, MA, and FD can be set on every Cisco switch. (ND only on some, for example Cat6500.) Settings are only effective if done on root bridge or switch; and if done, must be recalculated when you add or remove switches from the network, changing the ND.

Hope this helps.