RSTP CPU Utilization

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Nov 5th, 2008
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Hello Everybody,


I was planning to implement redundancy at core level by using once C4506 and a 3750G switch using HSRP and the trunks from various distribution layer switches would be connecting each of these switch. Primary trunk to C4506 and the copper uplink (secondary) to the 3750G. For which I also want to enable Rapid-PVST mode. So that for half of the vlans, C4506 would be the root bridge and for next half 3750G would be the root bridge. Please let me know will the CPU utilization a concern here. If so how can that be reduced? Let me know if through any design we can acheive the redudancy.


Thanks

Arabinda

Arabinda

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Calin Chiorean Wed, 11/05/2008 - 06:43
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Hi!


Normally you do not have to worry about CPU or other resource utilization, as RSTP is very often in use (I speak from experience) and it's designed to work with those devices. But if you have will encounter a loop or other problems (UDLD, link unstable causing recalculation,...) then the resources utilization will be higher than normal. How many vlans do you have there?


Cheers,

Calin

arabindas Wed, 11/05/2008 - 06:48
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Hi Calin,


Thank you for your response. We have around close to 40 vlans out of which 20 vlans are on the switch (Vlan interface created) and rest are configured on a ASA connected to C4506 switch.


Also close to 10-12 servers connections need to distributed across both the switches.


I feel to give more stability to the 3750G, shall I stack another 3750 switch to it?


Thanks

Arabinda

Calin Chiorean Wed, 11/05/2008 - 06:51
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Hi!


Instead of stacking 2 x 3750, better use in both sides 3750 and eliminate the C4506. This is what I would do if it is possible. You should not have problems with those vlans.


Good luck!


Cheers,

Calin

arabindas Wed, 11/05/2008 - 06:58
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Hi Calin,


Since already then C4506 is on network, and the servers and routers are connected to it. It would be difficult to remove the switch. So was just planning to loadbalance and provide some backup by introducing 2 stacked 3750 switches. Hope that works.


Thanks

Arabinda

Calin Chiorean Wed, 11/05/2008 - 07:03
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Hi arabindas!


For sure you can let the C4506 in place and stack the other 2 x 3750. In this way you have enough resources on both sides, and in case that one side has a failure the other one can sustain all the traffic.


Cheers,

Calin

satish_zanjurne Wed, 11/05/2008 - 06:43
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I don't think so , CPU utilization is concern here.


But why you are using one C4506 & other C3750G ?


If possible try to use both C4506 or both C3750G



arabindas Wed, 11/05/2008 - 06:50
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Hi Satish,


Thank you for your response.


The C4506 is already in the network, so we cannot replace that and due to budgetary constraint we cannot take another C4506 switch. Si I have arranged for two 3750 series switch. If one 3750 is not suitable to handle the load, then possibly I can try to stack two 3750.


Thanks

Arabinda

ralphcarter Wed, 11/05/2008 - 09:10
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Arabinda,


See if you can manually prune vlans off the trunk that are unneeded, this will reduce your spanning-tree instances and CPU.


The 3750Gs work very well as a layer 3 switch. Make sure you dont run too many etherchannels because you will face contention problems. Also, jumbo frame routing is not supported on the non-E 3750's.


Hope it helps.

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