From: Karl Jeacle (karl at domain jeacle.ie)
Date: Wed 11 Sep 2002 - 09:34:40 IST
On Wed 11 Sep 02, 07:59:07 +0100, Paul Kelly wrote:
> So the answer is exceptionally poor choice of router then - but is that
> what they're selling with the Multi service? I thought it was a Zyxel
I'm obviously not explaining this very well. The SpeedTouch Pro is
a bridge, and was selected primarily for use with the "multi"
service. That service is the same as "solo" except you have multiple
accounts, so you need a bridge with multiple ethernet ports. The
SpeedTouch Pro is not sold or provided as a router. If (for whatever
reason) you are supplied with the SpeedTouch Pro on the "enhanced"
service, you are expected to add your own two-port ethernet router
to run PPPoE.
> Does anyone know why they went with PPPoE instead of PPPoA?
There are various reasons, but presenting the customer with ethernet
instead of ATM would be the main one.
> PPPoE seems to be a dead loss - you lose a percent or two on the
> bandwidth
What you lose on bandwidth with PPPoE is completely dwarfed by what
you lose at the underlying ATM layer, so this is the least good
reason not to use PPPoE. The pros/cons of PPPoE are a whole other
discussion, and this thread is already way off-topic!
> and if you're not careful you get hit by the many sites out there
> that send you 1500 byte packets with the 'Do not fragment' flag set
> and can't fit the 1492 MTU on PPPoE :-(
This will never happen if your MTU is set to 1492. TCP will ensure
that the MSS is set appropriately low so that all packets will get
through. The issue only arises is if you don't set your MTU to 1492
(and you should always do this when using PPPoE, so the argument
doesn't really count), and then rely on Path MTU discovery to work.
In this case, you will hit trouble if people are blocking ICMP at
routers, but PMTU breaking is not a problem peculiar to PPPoE.
Karl
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