[c-nsp] Spanning-tree ports cost Formula

[Phil Bedard]

The newer versions of the STP standards (802.1D udpdated and 802.1W/S)
have updated path cost values to cover higher speeds.

10 Mb/s 2000000
100 Mb/s 200000
1 Gb/s 20000
10 Gb/s 2000 
100 Gb/s 200
1 Tb/s 20 
10 Tb/s 2 

Cisco switches generally need a command documented in this article to
enable the 32-bit length cost values (versus the old standard 16-bit).
Juniper switches use the 32-bit values by default, not sure about other
vendors.  Even then the defaults are usually the old values to
interoperate with other switches.

http://www.networkworld.com/community/node/57598


Phil 



On 11/11/13, 4:39 AM, "M K" <gunner_200 at live.com> wrote:

>Thanks for the replies , I just wanted to know how these values were
>extracted or if there was a specific formula like the one used for EIGRP
>metric or OSPF cost
>BR,
>
>> Date: Sat, 9 Nov 2013 21:09:22 +0000
>> From: A.L.M.Buxey at lboro.ac.uk
>> To: eng_mssk at hotmail.com
>> CC: gunner_200 at live.com; cisco-nsp at puck.nether.net
>> Subject: Re: [c-nsp] Spanning-tree ports cost Formula
>> 
>> Hi,
>> >    I think what he is asking for is how try the values were extracted
>> 
>> they are just default values for different interface types.
>> I dont recall there being any formula (unlike eg OSPF/EIGRP calculations
>> on links). cant recall if its CCNA or CCNP SWITCH level stuff:
>> 
>> Spanning tree port cost (configurable on a per-interface basis‹used on
>>interfaces configured as Layer 2 access ports)
>> 	
>> €10-Gigabit Ethernet: 2
>> €Gigabit Ethernet: 4
>> €Fast Ethernet: 19
>> 
>> 
>> obviously this is of interest to those doing >10Gb links... 40Gb and
>>100Gb
>> only appear to have '1' to share ;-)
>> 
>> alan
> 		 	   		  
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