Re: [dhcwg] dhc wg last call on agentopt-delegateand srsn-optiondrafts

I'm not sure why we're talking about dynamic routing protocols.

So bear with me while I nitpick and quibble about the topic I'm
not sure we should be debating.  The real content is after the
'===' break below.

On Mon, Feb 12, 2007 at 08:16:34PM -0500, Woundy, Richard wrote:
> I believe you are correct. According to RFC 2740 (OSPF for IPv6), an
> AS-external-LSA may include a "forwarding address"; see sections 3.4.3.5
> and A.4.7.

Huh, I had no idea OSPF could do that.  I doubt the facility is well
used.

But I'm not sure why a modern network operator would use OSPF for
their "non-connected" IGP, so it's rather strange to postulate that
situation.

The general practice I've engaged in is to use OSPF only to distribute
connected routes (subnets attached to routers' interfaces), and then
to use BGP to distribute any static bindings, which are customer
attachments that lack dynamic impetus, or any redistributed routes
from other routing protocol states (such as a unique OSPF protocol
state declared specifically to carry dynamic routes from a
customer).

In summary, the IGP carries prefixes directly connected to interfaces
on routers, and BGP carries prefixes delivered to their remote ends.

Both OSPF and ISIS have trouble scaling to large numbers of routes
(even with areas there are low ceillings), so this works much better.
Minimizing the size of the IGP, and maximizing the number of routes
carried by BGP, which is more efficient at the task of carrying routes
in bulk.

This is not a different protocol from BGP, but the operational practice
is commonly referred to as "iBGP" to differentiate between the task
of carrying routes internally or externally.

I'd honestly be pretty suprised if there were a single operator today
that used BGP only for the aggregates they advertise externally, and
consequently relied entirely upon OSPF (or even ISIS) for every
more-specific route.

So I'd also be pretty surprised, were I still an operator, if my
IETF representatives came to any conclusions about how a system
would work in my network based upon the principle of OSPF networks
stuffed to the gills.

> OSPF areas, implying that the DHCP server needs to participate in all
> relevant OSPF areas.

IFF you use "i"BGP, you require only one TCP connection over which
to process BGP commands.  Most operators would probably want more
than one, and probably would also want more than one DHCPv6 server
to perform the announcements, preferrably in different geographic
locations.

There are already quite appropriate tools in BGP router
implementations for limiting the number of routes advertised to
neighbors that don't wish to (or can't) carry a full table.

I see no reason why a single generic filter can't be made to
define "routes for CMTS's in facility X".

> In the worst
> case, the delegated prefix is reachable from the Internet through
> another network path (perhaps unknown to the DHCP server), but because
> the delegated prefix is advertised by the DHCP server, traffic is drawn
> to the CMTS and is blackholed. It might even be possible for a routing
> loop to form.

This is the first time I think anyone has suggested that DHCPv6
delegated prefixes in this case would be administratively controlled
by multiple independent entities.

I understood that if the client was using the same prefix, and connected
at a different location, that it would contact the same (or same group
of) DHCPv6 servers.

===  What was the question again?

As I said, I'm not sure why we're talking about dynamic routing
protocols.

In the various discussions we've had about this, it's been stipulated
that one requirement is that the CMTS not be required to participate
in any dynamic routing protocol at all.

So the very notion should be impossible.  We shouldn't even be
able to consider a routing protocol solution to a problem that,
I thought I understood, must span networks that do not implement
any routing protocols.

The implication being that the CMTS would enter only a local
"pseudo-static" route in its table, thanks to this option.  The
"real" router it was connected to (possibly via other similarly
non-dynamically-routing devices) would advertise the prefix's
route dynamically (by also participating as a DHCPv6 relay, and
being delivered similar options).

Basically, to use DHCPv6 relay chaining to reach a router that
does participate in dynamic routing, which either advertises
the delegated prefix or relies upon external routing updates
to direct it to send routes to the nearest non-dynamic router.

This implication is reinforced by reports from various people in
the WG and without, that CMTS operating software does not implement
dynamic routing protocols, is not provisioned with sufficient
processor power or memory (even to manage a "small" local network),
or...since CMTS people are "RF people" and not "IP people"...simply
aren't well suited in their implementation of the protocols.

So I'm pretty confused by looking at a routing protocol centric
view of solutions to this problem (which I thought was an impossible
candidate), and placing upon it criticisms for limitations that are
both the same and measurably worse in this DHCPv6-option centric view
I've been delivered previously.

So I don't get it.  Either I'm dense (probable), the problem hasn't
been explained sufficiently (possible), or there are so many
problems and solutions that no one can keep them straight.

So, may I make a suggestion?

Let's have another look at draft-stenberg-pd-route-maintenance.

I think at least one thing that has caused us to stumble is that
RAAN is intentionally so general-purpose that none of us seem to
agree about what it's going to be used for.  The very first things
I imagined by reading it were counterpositive to the CMTS
environment that's been postulated ever since.

He's already done a lot of great work towards enumerating the problems
and solutions.  If we could all take a moment to make sure they're all
in there, and if Markus and Ole are willing, I'd like to get a handle
on it.

I feel somewhat responsible since my abstention was more vocal than
I would have liked.  I don't know how much time I'll have until Q2
'07, I've probably already spent too much time "away from my desk"
just writing this (unjustifiably long) email this morning.

-- 
David W. Hankins	"If you don't do it right the first time,
Software Engineer		you'll just have to do it again."
Internet Systems Consortium, Inc.	-- Jack T. Hankins

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