[c-nsp] Maximum switched ethernet daisy chain size

[Pavel Skovajsa]

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
http://img171.imageshack.us/img171/3777/hop18kn4.jpg.

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?

Regards,
Pavel

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
choice