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Re: AW: draft-wbeebee-ipv6-cpe-router-04 comments
Hi Alan,
On Sun, 29 Mar 2009 21:09:37 -0400
"Alan Kavanagh" <alan.kavanagh@ericsson.com> wrote:
> Correct, and this is why SP's are not too keen to have routing localised
> in the aggregation network before the BNG.
>
I'd have thought they should be keen to avoid that, unless all of their
customers are all under or likely to all under surveilence at the same
time!
The technical requirement of LI is that traffic has pass the
interception point. As the majority of people are honest, it seems to
me that optimising the topology to pass the interception point, rather
than for best throughput and lower latency, is wasteful, and an unfair
performance and ultimately a network capex and opex cost burden on
those subscribers who aren't under surveilence, and may never be. Only
traffic that is to be lawfully intercepted should be forced past this
interception point, if it doesn't already naturally traverse it.
Some topologies would inherently make the BNG the best traffic
interception point e.g. wholesale broadband aggregation via L2TP.
However, for other topologies (e.g. a single VLAN interconnecting
customers' ADSL routers, and an upstream default router for access to
the Internet/other services), traffic can travel direct between
subscribers / their CPE, as the CPEs have an on-link peer relationship.
Should lawful interception be required, either that on-link path could
be changed to traverse the interception point (e.g., by mechanisms
such as forced forwarding), or better yet, the interception point be the
suspect subscriber's point of interconnection i.e. the specific ADSL
service that they're using - as all their traffic is naturally going to
traverse that point.
If an SP wants to have a topology that has all traffic traversing the
BNG, or is forced to because of a legal requirement, that's fine.
My argument is that other SPs won't have this requirement so they
shouldn't also be forced to adopt this LI optimal topology - they
should have the freedom to implement a topology optimised for
throughput and low latency.
So, getting back to the discussion point, I think there would be
value in having a mechanism where downstream CPE can be informed of
on-link peer-CPE's assigned prefixes, without the CPE themselves having
to trust each other's announcements. An idea I had a while back was a
"prefix redirect", similar to an ND host redirect, issued by, and only
accepted from, the upstream on-link default router. Not quite as
optimal as the CPE themselves announcing their prefixes via a routing
protocol, but it would be more scalable - the CPE would only be
maintaining topological knowledge for destinations they're currently
using, rather than for all the destinations they can reach via on-link
peer CPE.
Regards,
Mark.
> -----Original Message-----
> From: owner-v6ops@ops.ietf.org [mailto:owner-v6ops@ops.ietf.org] On
> Behalf Of Alastair Johnson
> Sent: March 28, 2009 1:41 PM
> To: Mark Smith
> Cc: Mikael Abrahamsson; Olaf.Bonness@telekom.de; v6ops@ops.ietf.org
> Subject: Re: AW: draft-wbeebee-ipv6-cpe-router-04 comments
>
> Mark Smith wrote:
> > On Thu, 26 Mar 2009 17:53:05 +0100 (CET) Mikael Abrahamsson
> > <swmike@swm.pp.se> wrote:
> >
> >> On Thu, 26 Mar 2009, Olaf.Bonness@telekom.de wrote:
> >>
> >>> Normally the customers are separated from each other by split
> horizont mchanisms and MAC adress translation techniques.
> >> Yes, but that defeats the whole purpose of the proposal from Mark
> >> Smith if I correctly interpret the scenario he proposed.
> >>
> >
> > Yes it would defeat it. The only reason I can think of to require hair
>
> > pinning of traffic between downstream on-link peer CPE is if your
> > default router is your traffic billing point, and you want to bill
> > (count) the traffic between those CPE. Otherwise you're probably
> > unnecessarily forcing a P2P model connectivity model (i.e.
> > an ATM ADSL backhaul model) onto a multi-access technology (an
> > Ethernet/ADSL backhaul model).
>
> Lawful Interception is another reason that a service provider may want
> all traffic from a subscriber aggregated to the default router. There
> may be no way around this, depending on the LI requirements that are
> placed on the service provider, and where the logical interception point
> is (BNG vs. DSLAM).
>
> aj
>
>