*From:*James Bensley <lists+uk...@bensley.me>
*Sent:* 22 July 2022 08:20
*To:* uknof@lists.uknof.org.uk; Paul Bone
<paul.b...@probitas-solutions.tech>
*Subject:* Re: [uknof] Policing vs Shaping in the UK
As Mark has already said, I think most telco's prefer policers
otherwise you're adding latency into your customers traffic. Most
national Ethernet services are providing a "dump" L2 pipe. Any decent
provider should set the policer CIR to the rate you're paying for so
you should be able to achieve it easily with UDP testing. If you want
to then add shapers and priority queuing etc to your devices at each
end, you can, but the provider should provide a dump pipe with
guaranteed bandwidth.
Also I think ingress policers at each end of the service is more
common. This is the way it is with Sky Ethernet for example. Egress
policers or shapers means that excess traffic is carried all the way
across the network, just to be dropped, so you really want ingress to
stop wasting bandwidth. Also most devices only support policers on
ingress (you can't control what someone else sends you, so
implementing ingress shapers is hard), and policers or shapers at
egress, but if you're limiting at ingress at both ends you don't need
any egress limiting.
Classic Ethernet switches were typically bad at support egress policing.
Broadcom chips seem to also typically struggle with egress policing, but
it looks like some vendors have found solutions to that problem, while
others haven't.
Custom silicon will generally support egress policing, but those get
pretty pricey.
I suppose the challenge with policing only on ingress on both sides of
the circuit is that if the customer is running a number p2mp circuits
from a single head-end, it's difficult to do that if each VLAN has a
different bandwidth requirement. For such cases, better to do the
policing on the upstream router, which means you may waste some
bandwidth on the 802.1Q trunk between the switch and router, but at
least it's not traversing the entire backbone.
Mark.
