Re: Benefits of switching at L2

["Dorian R. Kim" <dorian () blackrose org>]

On Sun, 13 Jul 1997, Alan Hannan wrote:

>   These two benefits 
>   
>       - L3 detached reroutes 
>       
>       - endpoint pair flow control
>
>   are significant.

And as significant as these benefits are, one must not also forget about the
significant disadvantages of L2 switching that comes with current 
implementations. TANSTAAFL.

By having two seperate intelligent networks that do not communicate with each
other, one is incurring the cost of greatly increased systemic complexity as
well as chances of failure mode amplification and obfuscation between L2 and
L3 infrastructure. 

By adding complex devices to L2, one addes more candidate for failures, and
shorten mean time between failures of one's network elements.

Furthermore, L3 detached reroutes has it own share of problems.

Whether this trade off makes sense is up to the individual networks, but like
all things each choice has it's own pains and pleasures. 

I personally prefer to keep L2 as simple as possible, and leave L3 to do its
thing. I guess it's a different interpretation of "segment the
responsibility."

>   But for many folk [large providers] with many problems [large
>   networks, weenie routers] L2 switching is helping to allow
>   networks to grow as stronger routers are built.

This is the key point. If there were real routers to buy, much of the fun
games that are played by various folks would be unnecessary. Furthermore,
there is no reason why L3 network can't implement things like end pair traffic
management much the same way L2 networks can given correct implementations.

-dorian