Fred,
I would like to better understand the particular use case offered as a
counter-example. One version of this counter-example is described in Section
2.3 of draft-baker-rtgwg-src-dst-routing-use-cases-01 (Specialized Egress
Routing). I have copied figure 3 from that draft below.
,-------.
,-' `-.
,---. ,-----. ,' `.
/ \ +-+ ,' `. / \
/ +---+R+-+ ISP 1 --+--- \
/ \ +-+ `. ,' ; :
; Customer : `-----' | The Internet |
| Network | ,-----. : ;
: ; +-+ ,' `. \ /
\ +--+R+-+ ISP 2 ) \ /
\ / +-+ `. ,' `. ,'
\ / `--+--' '-. ,-'
`---' | `-------'
Some specialized
Service
Figure 3: Egress Routing with a specialized upstream network
If a customer network homed to ISP1 and ISP2 (with PA prefixes S1 and S2) needs
to reach a destination prefix (D2) associated with a service offered by ISP2,
then the customer network can route all traffic with destination address in D2
to ISP2 using existing destination-based routing. R for ISP2 would originate a
route for D2. This route for D2 will be used throughout the customer network
instead of the default destination route originated by R for ISP1, due the
longest prefix match rule. The counter-example assumes that the host is smart
enough to use the source prefix S2 when sending packets to D2, so it will meet
the requirement that packets using the special service MUST use the special
service's source and destination addresses.
Therefore, it seems to me that pairing a source prefix with an arbitrary
destination prefix is not required to support the Specialized Egress Routing
use case in draft-baker-rtgwg-src-dst-routing-use-cases-01. In any case, it
would be useful to come to agreement about what is required to address the
Specialized Egress Routing use case described in
draft-baker-rtgwg-src-dst-routing-use-cases-01.
If instead the counter-example use case described below is different from
Specialized Egress Routing use case in
draft-baker-rtgwg-src-dst-routing-use-cases-01, it would be useful to describe
that use case in more detail so that we can evaluate it more thoroughly.
Thanks,
Chris
-----Original Message-----
From: Fred Baker (fred) [mailto:[email protected]]
Sent: Thursday, March 24, 2016 11:37 PM
To: Chris Bowers <[email protected]>
Cc: [email protected]
Subject: Re: multi-homing for provider-assigned IPv6 addresses
> On Mar 24, 2016, at 9:32 PM, Fred Baker (fred) <[email protected]> wrote:
>
>
>> On Mar 24, 2016, at 4:34 PM, Chris Bowers <[email protected]> wrote:
>>
>> It seems to me that most use cases for ipv6 multi-homing with
>> provider-assigned addresses only need to route based on source address when
>> the destination prefix is the default route. So why not require that source
>> prefixes can only be paired up with the default destination prefix ::/0?
>
> When what one has in mind is an egress route, that probably makes sense.
> However, it precludes an entire class of use cases mentioned in the use case
> draft. Why do that?
Let me give you an obvious variant. Imagine, if you will, that I have a PA
prefix from each of N ISPs, and therefore a default route to each of N ISPs.
Imagine also that I have a particular prefix that I would like to route through
via a given one of those N ISPs, in the special case that I happen to have been
smart enough to use that source prefix. So now I have N+1 source/destination
routes - unless you tie it to default routes.
A premature optimization usually breaks things...
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