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what is the maximum number of switches i can have an  single L2 domain running PVSTP ?

Posted on 2012-03-17
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Last Modified: 2012-03-21
I need an answer for the below questions , the answer should be with a trusted answer with refrence
what is the maximum number of switches i can have in a single l2 broadcast domain?? , in another words if i want to make a LAN , what is the maximum number of switches i can have? what is the best practice?  what can go wrong if I have many switches?
if in my network  an interface was flapping can this cause huge number of TCNs and will lead to high CPU ? if correct , how to protect my network from such a thing ?
what are the causes of high CPU in switches in a network in general ?
if my network is configured with udld protection , can high CPU trigger UDLD and my switches will go down ? moreover ,  if my switches was not exchanging BPDUs can thing cause udld to be triggered ?

if there is a duplex misatch can this lead to a seriose problem in the network ?
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Question by:Al_Muheiri
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by:Darr247
ID: 37735299
In my opinion you're asking too many questions with one post.

> what is the maximum number of switches i can have in a single l2 broadcast domain

Unlike hubs, in which all ports belong to the same collision domain, there is no maximum number of switches you can have between any 2 points in a layer 2 broadcast domain, because every port on a switch is its own collision domain. VLANs don't really change that.

Needing to cite references smacks of homework questions, by the way.
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by:eeRoot
ID: 37735425
There is no single answer because it depends on the network topology, VLAN setup, and the amount of network traffic being generated.  The simplest answer is, you can keep adding things to your network until you use up all the available bandwidth or until you run out of IP addresses.
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by:Al_Muheiri
ID: 37736341
Thanks Darr247 & eeRoot but still it seems there is no reffrence on this and the other questions is still has not been answered :(
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mat1458 earned 500 total points
ID: 37736666
>what is the maximum number of switches i can have in a single l2 broadcast domain?
no defined limit, you can have multiple broadcast domains in each switch

>what is the best practice?  
depends on the goal you want to achieve with the switches: client access, data center, manufacturing, ISP, ASP, etc. etc.

what can go wrong if I have many switches?
>question is far too general to give a specific answer. depends on the network design you have, the type of switches, the software versions, specific implementation issues. generally spoken you can say that less is more - the fewer switches you have the easier is the management and the control of the individual device. but if you have a specific requirement for a high number of devices this can be organized in a way that you are able to manage it.

>if in my network  an interface was flapping can this cause huge number of TCNs and will lead to high CPU ?
for a user port (Cisco terminology portfast) it does not cause a TCN so it shouldn't cause too much hassle. I guess that other switch manufacturers have similar features, however I don't know them. If an uplink flaps, then yes. But you hopefully notice that through your network management. (see http://academy.delmar.edu/Courses/download/CiscoIOS/CiscoSwitch_UnderstandingSpanningTreeWhenNetworkChanges.pdf)

if correct , how to protect my network from such a thing ?
use spanning-tree portfast or similar features on end system ports

>what are the causes of high CPU in switches in a network in general ?
spanning tree issues, large snmp requests, any type of attack, scan type of applications in the network, configuration issues with CPU intensive features

>if my network is configured with udld protection , can high CPU trigger UDLD and my switches will go down ?
If the UDLD process does not get it's amount of CPU that it needs for the generation of UDLD frames: yes. High CPU is a critical situation for any device so you can't really preview what is still running without flaws and what is impacted. It again depends on the sum of the features you are using on the box.

>moreover ,  if my switches was not exchanging BPDUs can thing cause udld to be triggered ?
I don't see any correlation between missing BPDUs and UDLD. UDLD is checking the bidirectionality of the L2 link between two switches whereas BPDU implicitly rely on that bidirectionality. So it's the other way round: UDLD can lead to missing BPDU and spanning tree recalculations.

>if there is a duplex misatch can this lead to a seriose problem in the network ?
Again the answer is "it depends". If the mismatch is on an end system port my answer would be no, even that your end users might disagree, if this happens on the interface of your file server. If the mismatch is on an uplink between switches then definitely: yes. The network will degrade as soon as larger volumes of traffic try to pass that link.
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by:Darr247
ID: 37737493
> what can go wrong if I have many switches?

Your DHCP server could exhaust its scope.

Reference: my brain
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by:Al_Muheiri
ID: 37747354
mat1458 has provided the Best answer
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