network diameter

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Mar 27th, 2007
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Hi forum,


10mbps has a diameter of 2500m

100mbps has a diameter of 205m

1000mbps has a diameter of 200m


if I have this setup:


PC - switch -..100 switches - PC,


I have a mix of 10mbps switch, 100mbps switch, 1000mbps switch in between, so long the distance between the switch is less than 100 meters, can I say I am still fine with the setup?


I cannot understand the diameter portion.


thanks much,

py

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mahmoodmkl Tue, 03/27/2007 - 21:47
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Hi


I think network diameter is counted on the basis of how many switches do u have between the root switch and the switch in question.


Cisco recomends to have not more then 7.


Thanks

Mahmood

paulnigel Tue, 03/27/2007 - 21:52
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Hi Mahmood,


Thank you for your reply.


Is the root switch being the STP root? say if I use my core switch as my root. Does it mean that If I am cascading down or downlinks to other 6 switches, I am fine? What about the distance? if I am using 100mbps port to cascade or downlink, does it mean that it shouldn't exceed 205meter?

mahmoodmkl Tue, 03/27/2007 - 22:37
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HI


Yes u right u can use upto 6 switches down u r core switch.100 mbps supports up to 100 meters.If u place a switch in this distance u will be fine.if u r going to connect the other switch with the last switch again u can go upto 100 mts.


Thanks

Mahmood

paulnigel Tue, 03/27/2007 - 23:02
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Hi Mahmood,


I dont quite get you. Are you trying to say, i can do like this:


core switch -100m-sw1-100m-sw2-100m-sw3...sw7-User PC.


so, the total length from the core will be 600+ meters. May I know what is this 205m diameter for 100mbps meant for?


Thanks much,

py

Jon Marshall Tue, 03/27/2007 - 23:47
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Hi


I think there is some confusion here. The diameter you are referring to is to do with half-duplex connectivity - see figure 7.1 in the following link


http://www.cisco.com/en/US/tech/tk1330/tsd_technology_support_technical_reference_chapter09186a008075974f.html#wp1020617


the diameter Mahmood is referring to is the diameter of the switch network so they are not the same thing.


If you run all your connections in full duplex mode this diameter (205m) should not be an issue for you.


The diameter Mahmood is referring to is how many cascaded switches you have within your layer 2 network. As he says Cisco recommends a limit of 7.


HTH


Jon


paulnigel Wed, 03/28/2007 - 00:43
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Hi Jon, Mahmood,


Thank you very much for the clarification.


When you say, if the connection is in full duplex mode, are you referring to the downlinks or cascading link?


My scenario is I have my core switch link to numerous remote racks, some rack is linked to other rack, sometimes more than 3 racks connected through switches before linking back to the core switches. within each rack, there are switches cascading down from the distribution switch, can be as many as 8 switches(sometimes 3com). Is that ok? for all the links, since it is less than 100 meters, we use cat5e cable for that. I am not sure this type of infrastructure will create problem.


Thanks much,

paul

Jon Marshall Wed, 03/28/2007 - 00:50
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Paul


Referring to all links really. Your switch links should be running in full duplex mode anyway i would hope. As far as the end host connections these can be full or half altho full is generally better.


If you have a core switch and 6 switches connected into them separately then your network diameter is 1.

If you have a core switch and one switch (SW1) plugged into it and then another switch (SW2) connected to SW1 up to 6 switches then your network diameter becomes 6.


Cisco recommned a maximum of 7, it is a recommendation from years of experience but it is not a hard and fast rule. You can go above it but you may start to see STP (spanning-tree) issues amongst other things.


HTH


Jon

paulnigel Wed, 03/28/2007 - 00:56
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Hi Jon,


Thank you very much for the explanation. I think I got it.


thanks,

paul

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