Subject: [Autoconf] About unique/non-overlapping prefixes terminology

From: Carlos Jesús Bernardos Cano <[email-masked]>
Date: Wed, 05 Dec 2007 23:23:07 +0100

Hi all,

	Regarding the discussion about what a unique prefix is and what is the
more appropriate term, I have some comments/questions/suggestions that I
wanted to share.

	To my understanding, each MNR might be delegated a prefix(es) to be
used to configure its(their) interfaces and further delegate (i.e.,
assign) addresses to attached non-MANET hosts. In that sense, I see that
those prefixes should be non-overlapping, meaning that the IPv6
addresses that might be configured out of several different IPv6
prefixes must not overlap (i.e. have to be different). This does not
mean that MNRs may be delegated a bigger prefix (e.g., a /48) and then
delegate further this prefix to other routers (MNRs or normal routers),
but at the end, the prefixes used by the end-routers must not overlap.

	Aggregation is a different thing. In the Internet, we have see
aggregation to reduce the number of routing entries and so on, but the
global prefixes that are deployed in the subnets do not overlap.

	A MNR can also be delegated prefixes/addresses to be used for
configuring its MANET interfaces. Of course, these should also be unique
in the same sense. If a MNR is delegated an address, then what "unique"
means is clear (the 128 bits are different from any other address used
within the MANET). If a MNR is delegated a prefix, the same comments
mentioned above would apply (i.e., this prefix must not overlap with any
other prefix used by any other MNR within the MANET).

	Is this view shared by others? Am I missing something (probably
yes ;->)?

	Regards,

	Carlos

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From: "Ian Chakeres" <[email-masked]>
Date: Thu, 6 Dec 2007 04:11:29 +0530

Based on the confusion around "unique" I've removed the use of 'unique
prefix' from my local revision. I've replaced unique with distinct.

Please let me know if you have another recommendation.

Distinct Prefix Assignment
MANET interfaces that are known to exhibit the above mentioned
properties must be configured with distinct prefixes, for their
non-link-local addresses. The reason for this requirement is so that
no two MANET interfaces are configured to appear within the same IP
prefix.

Ian Chakeres

---

From: Alexandru Petrescu <[email-masked]>
Date: Wed, 05 Dec 2007 17:35:35 -0800

> no two MANET interfaces are configured to appear within the same IP

Can I assign 2001:db8::/32 on one interface and 2001:db8::/33 on another 
interfaces of a MANET Router?  The prefixes seem distinct to me.

Can I assign 2001:db8::/32 on one interface and fd67:39d:7a3a::/32 on 
another?  They look distinct to me.

Just wanted to make sure for those two examples, thanks.

Alex

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From: Emmanuel Baccelli <[email-masked]>
Date: Thu, 06 Dec 2007 03:09:30 +0100

Alex,

> interfaces of a MANET Router?  The prefixes seem distinct to me.

well look again. These are obviously not distinct CIDR blocks, since one 
is contained in the other!

> another?  They look distinct to me.

there we agree.
Emmanuel

---

From: Alexandru Petrescu <[email-masked]>
Date: Wed, 05 Dec 2007 18:16:56 -0800

Emmanuel Baccelli wrote:
>> Can I assign 2001:db8::/32 on one interface and 2001:db8::/33 on 
>> another interfaces of a MANET Router?  The prefixes seem distinct to me.
>>
> 

I think we may have a clear contentious problem here :-)  I believe 
these two prefixes are distinct and could as such be assigned ok on two 
real Ethernet interfaces of a router.  Especially if these two prefixes 
are managed by other routers (but still assigned on the two interfaces 
of same router).

There are a few ways out of this:
-say that a MANET Router does not consider these two prefixes distinct.
-say that two MANET Interfaces do not consider these two prefixes
  distinct.
-say there may be a multilink issue problem with these two prefixes on
  two interfaces of same Router.
-say that they are distinct.

You think of other ways out of this?

Alex

---

From: "Templin, Fred L" <[email-masked]>
Date: Wed, 5 Dec 2007 18:38:56 -0800

> -----Original Message-----
> From: Emmanuel Baccelli [mailto:[email-masked]] 
> Sent: Wednesday, December 05, 2007 6:10 PM
> To: [email-masked]
> Subject: Re: [Autoconf] About unique/non-overlapping prefixes 
> terminology
> 
> Alex,
> 

I agree, and IMHO it is clear what is meant by distinct
or not.

Fred
[email-masked]

---

From: Alexandru Petrescu <[email-masked]>
Date: Wed, 05 Dec 2007 18:47:59 -0800

> I agree, and IMHO it is clear what is meant by distinct

Is 2001:db8::/24 contained in 2001:db8::/32?  I'd say yes.  Are they 
distinct?  I'd say yes too.

Alex

---

From: Carlos Jesús Bernardos Cano <[email-masked]>
Date: Thu, 06 Dec 2007 18:38:30 +0100

Hi Alex,

> are managed by other routers (but still assigned on the two interfaces 

	I think I disagree here. IMHO, it would not be ok to assign these
addresses on two real Ethernet interfaces of a router. If there is a
host attached to one of these interfaces, and the IPv6 address of this
host is, let's say 2001:db8::3, how does the router know to which
interface should deliver a packet addressed to 2001:db8::3? I guess the
router will try to deliver this packet though the interface configured
as 2001:db8::/33 (longest prefix match), but the host maybe as well
attached to the other interface, right?. Maybe it's a stupid question
and I'm missing something, sorry for the question.

	Thanks,

	Carlos

---

From: "Teco Boot" <[email-masked]>
Date: Thu, 6 Dec 2007 19:35:09 +0100

I would use terms unique address and non-overlapping prefix.
I think these terms are well known.

I think routers SHOULD NOT use overlapping prefixes and SHOULD NOT use
duplicate addresses.

Non-unique addresses are allowed, i.e. anycast. These are not
autoconfigured.
Anycast is overlapping prefixes also. Mostly one anycast address per link,
to circumvent problems with ND.
Another use case for duplicate addresses is router redundancy, e.g. VRRP.
Only one address is active in this case. Also not autoconfigured.

In NEMO, prefixes overlap. HA on home link has a prefix, this overlaps with
MNP. NEMO MRHA tunnel associates those two.

Teco.

---

From: Carlos Jesús Bernardos Cano <[email-masked]>
Date: Thu, 06 Dec 2007 19:41:47 +0100

Hi Teco,

> MNP. NEMO MRHA tunnel associates those two.

	Just a comment, in NEMO prefixes may overlap/be aggregated, but it's
not the only possibility. RFC4887 documents that.

	Regards,

	Carlos

---

From: Alexandru Petrescu <[email-masked]>
Date: Thu, 06 Dec 2007 11:02:33 -0800

Carlos Jesús Bernardos Cano wrote:
>>>>> Based on the confusion around "unique" I've removed the use 
>>>>> of 'unique prefix' from my local revision. I've replaced 
>>>>> unique with distinct.
>>>>> 
>>>>> Distinct Prefix Assignment MANET interfaces that are known to
>>>>>  exhibit the above mentioned properties must be configured 
>>>>> with distinct prefixes, for their non-link-local addresses. 
>>>>> The reason for this requirement is so that no two MANET 
>>>>> interfaces are configured to appear within the same IP 
>>>>> prefix.
>>>> Can I assign 2001:db8::/32 on one interface and 2001:db8::/33 
>>>> on another interfaces of a MANET Router?  The prefixes seem 
>>>> distinct to me.
>>>> 
>>> well look again. These are obviously not distinct CIDR blocks, 
>>> since one is contained in the other!
>>  these two prefixes are distinct and could as such be assigned ok 
>> on two real Ethernet interfaces of a router.  Especially if these 
>> two prefixes are managed by other routers (but still assigned on 
>> the two interfaces of same router).
> 
> addresses on two real Ethernet interfaces of a router.

We may have terminology problem :-)  Assigning a prefix to an interface
with ifconfig also adds an entry in the routing table... which part do
we disagree on?

> If there is a host attached to one of these interfaces, and the IPv6 
> address of this host is, let's say 2001:db8::3, how does the router 
> know to which interface should deliver a packet addressed to 
> 2001:db8::3? I guess the router will try to deliver this packet 
> though the interface configured as 2001:db8::/33 (longest prefix 
> match),

Right, that's what router would do.

> but the host maybe as well attached to the other interface, right?.

Same host attached to two interfaces of a router?  Or do you mean there 
may be two different hosts, each connected on one of the router's 
interfaces?  I guess this latter?  In this latter case:  I wouldn't 
recommend two different hosts attached to two interfaces of a router to 
use the same 2001:db8::3 address.  That's just a recommendation and 
people could configure the way they wish.

Doing that configuration (2001:db8::3 assigned to two different hosts) 
is not necessarily prohibited by the assumed aggregation of prefixes nor 
by the routing system.  Not sure how to say this better.

What if there is no host attached to the router's interface, but just 
routers.

What if one interface is the 'upstream', 'egress' interface and the 
other interface is the 'downstream', 'ingress' interface.  Like this:

           |
           | upstream 2001:db8::/32
        ------------
       |MANET Router|
        ------------
           | downstream 2001:db8::/33
           |

Alex

---

From: Alexandru Petrescu <[email-masked]>
Date: Thu, 06 Dec 2007 11:08:08 -0800

Teco Boot wrote:
> I would use terms unique address and non-overlapping prefix. I think
> these terms are well known.
> 
> I think routers SHOULD NOT use overlapping prefixes and SHOULD NOT
> use duplicate addresses.

Well I think they all use overlapping prefixes.  Most prefixes overlap 
up to some bit limit.  The only example of completely non-overlapping
prefixes I can think of are the ones differing in the first bit (eg
2001:db8::/32 and fd67:39d:7a3a::/32 differ at the first bit).

> In NEMO, prefixes overlap. HA on home link has a prefix, this
> overlaps with MNP. NEMO MRHA tunnel associates those two.

My NEMO can be configured with completely non-overlapping prefixes (home
link to be 2001:db8::/32 and fd67:39d:7a3a::/32 on the ingress interface
MNP).

Alex

---

From: "Teco Boot" <[email-masked]>
Date: Thu, 6 Dec 2007 20:13:48 +0100

> -----Oorspronkelijk bericht-----
> Van: Alexandru Petrescu [mailto:[email-masked]]
> Verzonden: donderdag 6 december 2007 20:08
> Aan: Teco Boot
> CC: [email-masked]; [email-masked]; 'Emmanuel Baccelli'
> Onderwerp: Re: [Autoconf] About unique/non-overlapping prefixes
> terminology
> 
> Teco Boot wrote:

Why are you trying to confuse all of us?

> link to be 2001:db8::/32 and fd67:39d:7a3a::/32 on the ingress

Great. But I think you can also configure overlapping prefixes. If not, I am
not interested in your NEMO.

Teco.

---

From: Carlos Jesús Bernardos Cano <[email-masked]>
Date: Thu, 06 Dec 2007 20:19:43 +0100

Hi Alex,

	See below...

> with ifconfig also adds an entry in the routing table... which part do

	I think assigning those two addresses to two different interfaces is
not a good configuration. Maybe when addressing your comments below I
make myself more clear.

> people could configure the way they wish.

	I tried to mean that that a host with the address 2001:db8::3 may be
attached to either the interface A of the router (the one with an
address from 2001:db8::/32) or to the interface B (the one with an
address from 2001:db8::/33), but I didn't mean the same host attached to
two different interfaces or two different hosts with the same IP
address.

	Maybe a picture helps here:

                | upstream (eggress) interface
                |
          --------------
      ----|MANET ROUTER|----
      |   --------------    |
  2001:db8::/32         2001:db8::/33
      |
      |
  ---------
  | HOST  | 2001:db8::3
  ---------

	How does the MANET router knows how to send a packet to the host? This
tried to be my question. Sorry if I didn't express that in a proper way
(not being a native speaker doesn't help me :-( ).

> other interface is the 'downstream', 'ingress' interface.  Like this:
	This is a different scenario from what I had in mind. Anyway, IMHO I'd
avoid this configuration as well, I don't like overlapping prefixes, but
maybe it's just a matter of personal opinion... what do other people
think?

	Regards,

	Carlos

---

From: Alexandru Petrescu <[email-masked]>
Date: Thu, 06 Dec 2007 11:24:40 -0800

Teco Boot wrote:
> 
>> -----Oorspronkelijk bericht----- Van: Alexandru Petrescu
>> [mailto:[email-masked]] Verzonden: donderdag 6
>> december 2007 20:08 Aan: Teco Boot CC: [email-masked];
>> [email-masked]; 'Emmanuel Baccelli' Onderwerp: Re: [Autoconf]
>> About unique/non-overlapping prefixes terminology
>> 
>> Teco Boot wrote:
>>> I would use terms unique address and non-overlapping prefix. I
>>> think these terms are well known.
>>> 
>>> I think routers SHOULD NOT use overlapping prefixes and SHOULD
>>> NOT use duplicate addresses.
>> Well I think they all use overlapping prefixes.  Most prefixes
>> overlap up to some bit limit.  The only example of completely
>> non-overlapping prefixes I can think of are the ones differing in
>> the first bit (eg 2001:db8::/32 and fd67:39d:7a3a::/32 differ at
>> the first bit).
> 

?  Sorry about that.  In short:  Mainly, people say that 2001:db8::/32
and 2001:db8::/33 are not distinct, thus they could not be assigned on
two MANET interfaces (per Ian definition).

Ian proposed a definition of Distinct Prefix Assignment.  I checked two
examples of prefix couples being distinct in my view.  People disagree
on one of these couples having distinct prefixes: they see it as one
contained into another, and thus not fitting the definition of Ian.

That's all.  If consensus says that these two prefixes are non-distinct
and can not be assigned on MANET interfaces then I'll abide to consensus.

>> My NEMO can be configured with completely non-overlapping prefixes 
>> (home link to be 2001:db8::/32 and fd67:39d:7a3a::/32 on the
>> ingress interface MNP).
> 
> Great. But I think you can also configure overlapping prefixes. If
> not, I am not interested in your NEMO.

That's right, I can configure both overlapping and non-overlapping 
(distinct).  However, Ian's definition only considers non-overlapping 
(distinct) prefixes.  Thus, Ian definition excludes NEMO MR for use in 
MANET.

(I use 'Ian definition' with no particular reference to a person, just
  to say what definition we talk about.)

Alex

---

From: "Templin, Fred L" <[email-masked]>
Date: Thu, 6 Dec 2007 11:25:34 -0800

> From: Teco Boot [mailto:[email-masked]] 
> Sent: Thursday, December 06, 2007 11:14 AM
> To: 'Alexandru Petrescu'
> Cc: [email-masked]; 'Emmanuel Baccelli'
> Subject: RE: [Autoconf] About unique/non-overlapping prefixes 
> terminology
> 
> 
> 

+1 (at least!)

Fred

---

From: Alexandru Petrescu <[email-masked]>
Date: Thu, 06 Dec 2007 11:28:55 -0800

Templin, Fred L wrote:
 >> From: Teco Boot [mailto:[email-masked]] Sent: Thursday, December 
06, 2007 11:14 AM
terminology
 >> Why are you trying to confuse all of us?

Sorry about that, I'll drop it here.

Alex