Re: weird Config... How long will this work?
- From: Bod43@xxxxxxxxxxxxx
- Date: Wed, 23 Apr 2008 04:46:28 -0700 (PDT)
On 23 Apr, 08:57, rober...@xxxxxxxxxxxx (Walter Roberson) wrote:
In article <6527c$480e2c23$544b0fc5$16...@xxxxxxxxxxxxxxx>,
stephan <banana.j...@xxxxxxxxxx> wrote:
a ring structure with 14 switches (29xx-class) in a chain.
------switch-----...----switch---|
| |
----------------------------------
... stands for 12 (!) more switches.
every switch to switch connection is done by a microwave-p2p-link
with 4 to 8Mb bandwith.
All switches have an IP adress in the same subnet (vlan1).
Q:
What does the customer has to expect?
If there is a single point to point failure, traffic will continue
to flow around the ring, possibly just having to take the long
way instead of the short route.
To find out whether this is an effective solution, one would
have to know the traffic patterns, the ETF (estimated time to failure),
whether failures are correlated (e.g., is the area prone
to hurricanes that might knock several links out of alignment?),
and the value that the customer places on maintaining connectivity.
If this is a closed private network, then going to a routing
protocol would be of benefit only to the extent that the routing
protocol might (if tuned properly) allow faster detection and
redirection than would otherwise be the case through Spanning Tree
Protocol.
Spanning Tree Protocol limits were traditionally given in terms
of number of hops, but with full duplex links, the -effective-
limit is on the latency of getting a query out from the potential
root node all the way to the furthest node and back again. You
don't happen to mention the distances involved in that microwave
link; if there is non-trivial latency involved, then the spanning
tree protocol might not be able to converge, in which case
a routing protocol would have to be used instead.
As Walter has implied the network is over the
802.1d STP maximum network diameter of 8 bridges.
First of all check the current standards, there have been
a number of changes in STP e.g. Rapid STP, and perhaps
this limit has been changed in some of the new variants.
As far as I am aware there is nothing that actually
enforces the 8 hop limit and with your simple network
topology and with modern equipment I would expect
STP would be expected to behave correctly.
The one thing that would worry me would be the
reliability of the radio links and the interaction of
unreliable links with STP. If the links did drop
packets you could consider changing the timers
such that either more or fewer hellos were lost
before re-convergence occurred.
If STP did turn out to be a problem you could consider
finding some switches that did not do STP at all
and were transparent to the STP packets.
With your topology it is only necessary to have a single switch
running STP, all of the others just have to pass that
switches STP frames. I don't know what the
behaviour of Cisco switches might be with STP
disabled with regard to the forwarding of STP packets.
.
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