Re: [j-nsp] interoperation between MSTP and old STP

[Victor Sudakov]

Ben Dale wrote:
> > 
> > I have several EX4200 switches with redundant links, all are running
> > MSTP with a couple of MSTIs.
> > 
> > If I include an older switch which can only run old-fashioned STP,
> > will they interoperate and still keep the topology loop-free? What if
> > it can run STP and RSTP, but not MSTP?
> 
> They will interoperate, however there are key differences to be aware of:

> - STP/RSTP forms topology with STP bridges regardless of whether
> correct VLANs are trunked on ports - this can mean that topologies
> may form that isolate VLAN segments if you haven't configured
> trunked ports correctly on all links

> - STP/RSTP bridges will treat an MSTP network (regardless of how
> many switches it contains) as single contiguous bridge, so you may
> find that the ports that block in your RSTP network aren't quite
> where you expected them to be when simply counting the radius from
> the root bridge.  

Ben, thank you for your explanation. 

> 
> > 
> > A link to some good documentation is also appreciated.
> > 
> > TIA for any input.
> 
> I highly recommend Petr Lapukhov's work here:
> 
> http://blog.internetworkexpert.com/2010/02/22/understanding-mstp/

I remember reading it when I set up MSTP for the first time, but I 
skipped the multi-region part of if. And the legacy STP link should
look to MSTP switches as a foreign region, from what I was told.


-- 
Victor Sudakov,  VAS4-RIPE, VAS47-RIPN
sip:suda...@sibptus.tomsk.ru
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Re: [j-nsp] interoperation between MSTP and old STP

[Ben Dale]

Hi Victor,

On 15 May 2015, at 6:06 pm, Victor Sudakov  wrote:

> Colleagues,
> 
> I have several EX4200 switches with redundant links, all are running
> MSTP with a couple of MSTIs.
> 
> If I include an older switch which can only run old-fashioned STP,
> will they interoperate and still keep the topology loop-free? What if
> it can run STP and RSTP, but not MSTP?

They will interoperate, however there are key differences to be aware of:
- STP/RSTP forms topology with STP bridges regardless of whether correct VLANs 
are trunked on ports - this can mean that topologies may form that isolate VLAN 
segments if you haven't configured trunked ports correctly on all links
- STP/RSTP bridges will treat an MSTP network (regardless of how many switches 
it contains) as single contiguous bridge, so you may find that the ports that 
block in your RSTP network aren't quite where you expected them to be when 
simply counting the radius from the root bridge.  

> 
> A link to some good documentation is also appreciated.
> 
> TIA for any input.

I highly recommend Petr Lapukhov's work here:

http://blog.internetworkexpert.com/2010/02/22/understanding-mstp/

The configuration and outputs are IOS-based and there are a few PVST+ interop 
discussions, but the supporting protocol description and break-down is truly 
excellent.

Cheers,

Ben
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Re: [j-nsp] interoperation between MSTP and old STP

[Patrick Okui]

On  15-May-2015 11:06:53 (+0300), Victor Sudakov wrote:
> If I include an older switch which can only run old-fashioned STP,
> will they interoperate and still keep the topology loop-free? What if
> it can run STP and RSTP, but not MSTP?

RSTP is backwards compatible with STP and MSTP is backwards compatible
with both (by design).

> 
> A link to some good documentation is also appreciated.

Hmm. Besides the RFCs I'd say

is a decent summary.

--
patrick



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[j-nsp] interoperation between MSTP and old STP

[Victor Sudakov]

Colleagues,

I have several EX4200 switches with redundant links, all are running
MSTP with a couple of MSTIs.

If I include an older switch which can only run old-fashioned STP,
will they interoperate and still keep the topology loop-free? What if
it can run STP and RSTP, but not MSTP?

A link to some good documentation is also appreciated.

TIA for any input.

-- 
Victor Sudakov,  VAS4-RIPE, VAS47-RIPN
sip:suda...@sibptus.tomsk.ru
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