>From other statements I've read (Cisco published material) and from the
original excerpt I published, I'd imagine that the placement of the root
does matter.
"Part of this restriction is coming from the age field BPDU carry:
when a BPDU is propagated from the root bridge towards the leaves of the
tree, the age field is incremented each time it goes though a bridge.
Eventually, when the age field of a BPDU goes beyond max age, it is
discarded. Typically, this will occur if the root is too far away from some
bridges of the network. This issue will impact convergence of the spanning
tree."
I'd think that if a bridge were to be the third bridge away from the root,
and another switch was the third bridge on the far side of the root, I
wouldn't expect to see any problems with MaxAge because I can't see the root
being too far from some of the bridges in the network. Now if a bridge were
to be the seventh, I could see how that would impose a greater delay and
possibly negatively impact the MaxAge parameter. Now my question would
be... does this really apply in today's networks or is this more of a
limitation of yesteryear's "software-based bridges"?
One day I'll dissect STP inside and out. One day...
-- Leigh Anne
> -----Original Message-----
> From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of
> Priscilla Oppenheimer
> Sent: Wednesday, August 29, 2001 3:17 PM
> To: [EMAIL PROTECTED]
> Subject: Re: What's the diameter of your switched network? [7:17489]
>
>
> At 07:27 PM 8/28/01, Gareth Hinton wrote:
> >Always thought that Diameter was a misleading term.
> >If the root bridge is physically in the centre of the bridged
> network, the
> >diameter is actually the radius.
> >Hmmm - more coffee - it's late.
>
> Hmm, it is late, but I don't think the placement of the root
> bridge matters
> in this question. The Cisco text says "This means that two
> distinct bridges
> in the network should not be more than seven hops away the one to the
> other." The English is awkward, but the meaning is clear and notice that
> there's no mention of the root bridge.
>
> IEEE 802.1D says that the recommended value for the maximum
> bridge diameter
> is 7, and its definition is "The maximum bridge diameter of the
> Bridge LAN:
> The maximum number of Bridges between any two points of attachment of end
> stations."
>
> Priscilla
>
>
>
>
> >""Leigh Anne Chisholm"" wrote in message
> >[EMAIL PROTECTED]">news:[EMAIL PROTECTED]...
> > > Here's something funky I've just started researching. Thought many of
> you
> > > might not be aware of this...
> > >
> > > Awkward STP Parameter Tuning and Diameter Issues
> > >
> > > We already saw that an aggressive value for the max-age
> parameter and the
> > > forward-delay could lead to a very unstable STP. The loss of
> some BPDUs
> >can
> > > then cause a loop to appear. Another issue, not very known,
> is related to
> > > the diameter of the bridged network. The conservative default
> values for
> >the
> > > STP impose a maximum network diameter of seven. This means that two
> >distinct
> > > bridges in the network should not be more than seven hops
> away the one to
> > > the other. Part of this restriction is coming from the age field BPDU
> >carry:
> > > when a BPDU is propagated from the root bridge towards the
> leaves of the
> > > tree, the age field is incremented each time it goes though a bridge.
> > > Eventually, when the age field of a BPDU goes beyond max age, it is
> > > discarded. Typically, this will occur if the root is too far away from
> >some
> > > bridges of the network. This issue will impact convergence of the
> spanning
> > > tree.
> > >
> > >
> > > This came from: http://www.cisco.com/warp/public/473/16.html#2f
> ________________________
>
> Priscilla Oppenheimer
> http://www.priscilla.com
Message Posted at:
http://www.groupstudy.com/form/read.php?f=7&i=17787&t=17489
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