Re: [Rstplib-users] RE: 802.1w: 3 questions about flushing

[<alb...@ya...>]

Hi All,
I have 3 questions about FDB flushing in .1w & .1s.

Question 1. tcWhile decrementing.
When Topology Change is DETECTED, the timer tcWhile
accepts
a value 4 (twice HelloTime). Then, the PTM binds
"topology
change flag" in BPDU. While in pure RSTP LAN there are
no
"topology change acknowledgements", this timer is
decremented
until 0 "by natural".
So, there are 2 outgoing BPDU with "topology change
flag": the
first – when tcWhile=4; the second – when tcWhile=2.
If the
considerations above are right, it seems, that Alex is
optimist:
it will be "triple" flushing, not double!

Question 2. Do we have to make FDB flushing for a
Port when this Port becomes "Disabled" (or, let us
say,
macOperational=FALSE).

Let us consider a Bridge and 2 stations U1 and U2.
Station U1 is connected to Port P1; station U2 - to
Port P2.
Station U2 sends ping responses to U2 and receives
ping
replies from it.

Now we disconnect U2 from P2 and connect it to the
Port P3.

While station U2 is silent (it acts as "passive" echo
server
and doesn't send anything without request) and
Filtering
Database entry that holds U2 on Port P2 continues to
be
valid, the Bridge forwards  responds to "disabled"
Port P2.
So, the poor U1 will not see U2 until ARP entry aging
:(

Question 3. In 1s: Do we have to make flushing per all
tags
in an MSTi ? And what about CSTi ?

Yours truly, Albina

 --- Shyam Kaluve <sk...@ci...> wrote: > Alex,
> 
> When a p2p link comes up and becomes part of the
> active topology, both
> ports connected by that link become topology change
> initiators. The set of
> ports that will be flushed for each of the
> initiators will be different,
> but yes, there will be a substantial number of ports
> common to both the
> sets and flushed twice.
> 
> For correctness you will need to flush the minimum
> set of ports only once.
> But since this operation is performed by each bridge
> in its own pace, once
> may be not enough. The residual traffic as the
> topology is converging may
> cause some ports to learn wrong destinations. So
> IMHO the standard should
> lean towards correctness than efficiency in this
> case. Next generation of
> bridge hardware will be more 802.1w friendly so this
> question may become
> moot.
> 
> -shyam
> 
> Note: All disclaimers apply.
> 
> At 10:24 AM 1/6/2002 +0200, Alex Ruzin wrote:
> >Ladies & Gentlemen !
> >Excuse me, routers & brouters are very interesting
> devices,
> >but what about my original question (double
> flushing in regular bridges) ?
> >Best regards, Alex
> 
> 
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