[c-nsp] Limits of STP/RSTP/REP?

[Tassos Chatzithomaoglou]

That was for Rapid PVST+ (cisco prop). MST doesn't use such timers, besides MST0/IST (probably for compatibility outside 
the region).

switch(config)#spanning-tree mst 0 root primary diameter ?
   <2-7>  Maximum number of bridges between any two end nodes

switch(config)#spanning-tree mst 1 root primary ?
   <cr>


Keep in mind that the diameter value is just an internal IOS kind-of-macro that just changes automatically all other stp 
timers according to its value. So you can configure a diameter of 7, check the produced timers and then take the risk 
and increase them further.

Also 802.1D-2004 proposes some values for max-age in accordance to other timers.

2 ? (Bridge_Forward_Delay -- 1.0 seconds) >= Bridge_Max_Age
Bridge_Max_Age >= 2 ? (Bridge_Hello_Time + 1.0 seconds)

--
Tassos

Ross Vandegrift wrote on 22/05/2009 17:15:
> On Thu, May 21, 2009 at 04:54:40PM +0300, Tassos Chatzithomaoglou wrote:
>> switch(config)#spanning-tree vlan 7 root primary ?
>>   diameter  Network diameter of this spanning tree
>>   <cr>
>>
>> switch(config)#spanning-tree vlan 7 root primary diameter ?
>>   <2-7>  Maximum number of bridges between any two end nodes
> 
> Are those are numbers for classic PVST?  RST allow for larger diameter
> networks because TCNs don't have to propogate to the root and then
> back down.  My numbers come from the MST version:
> 
> lab(config)#spanning-tree mst max-hops ?
>   <1-255>  maximum number of hops a BPDU is valid
> 
> Ross
> 
>>
>> --
>> Tassos
>>
>> Tassos Chatzithomaoglou wrote on 21/05/2009 16:43:
>>> I had the impression that STP diameter defined the max number of bridges 
>>> between 2 points.
>>> And the recommended value by the IEEE was 7 (using default timers).
>>>
>>> -- 
>>> Tassos
>>>
>>> ?????? ???????? wrote on 21/05/2009 12:25:
>>>>> Definitely not more than 20 in a ring.  As far as I know, IOS limits
>>>>> the value of max-hops to 20.  This means you can't have a BPDU
>>>>> traverse more than 20 hops without being thrown away.  If one pair of
>>>>> switches in the ring experienced a total cut, your network would have
>>>>> a diameter of 20, end to end.
>>>> this is STP limitation: MaxAge is by default 20 hops.
>>>> for IOS, you can change this value:
>>>>
>>>> Switch(config)#spanning-tree vlan 1 max-age ?
>>>>  <6-40>  maximum number of seconds the information in a BPDU is valid
>>>> or for MST
>>>> Switch(config)#spanning-tree mst max-age ?
>>>>  <6-40>  maximum number of seconds the information in a BPDU is valid
>>>>
>>>> value 40 is maximum bpdu hopcount for 3560 switch, for other models
>>>> there can be other upper limit.
>>>>
>>>> -- 
>>>> wbr
>>>> sergey khalavchuk
>>>> _______________________________________________
>>>> cisco-nsp mailing list  cisco-nsp at puck.nether.net
>>>> https://puck.nether.net/mailman/listinfo/cisco-nsp
>>>> archive at http://puck.nether.net/pipermail/cisco-nsp/
>>>

>