mack at exchange
Jun 7, 2008, 11:08 PM
Post #4 of 4
Maximum switched ethernet daisy chain size
[In reply to]
> Message: 3
> Date: Sat, 7 Jun 2008 17:50:59 +0200
> From: "Pavel Skovajsa" <pavel.skovajsa [at] gmail>
> Subject: [c-nsp] Maximum switched ethernet daisy chain size
> To: cisco-nsp [at] puck
> <323aca890806070850me92fb8bq53e7d8ef4e0d2841 [at] mail>
> Content-Type: text/plain; charset=ISO-8859-1
> Hello all,
> Recently I have found an interesting issue.
> I have found that on our network the packets that traverse more then
> 17 (18 and more) L2 ethernet switching hops all connected with MM
> fiber 1G links have lowered probability of arrival.
> The way I have found this is that our big ethernet ring with 30+
> switches was cut (fiber issue) behind 18th switch from L3 switch, and
> everybody hosted after 18th switch has some interesting packet loss
> issues.See the smokeping details for 18th switch on
> This is not very logical for me, as switched ethernet works based on
> store&forward method so no old-school 5-4-3 rule applies as in shared
> collision (hub) environment. Anybody has a good explanation why adding
> more L2 hops to the path tends to kill packets?
> p.s. yes I know that building large ethernet rings is generally not a
> good idea, however sometimes due to large distances you have no other
This sounds like a spanning-tree diameter problem.
Spanning-tree limits the number of intermediate switches between the root
and each end-point. Without tuning this value is 7.
This link describes possible issues with diameter:
This link may help you resolve the problem:
LR Mack McBride
Alpha Red, Inc.
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