Subject: extended communities questions and observations

From: Jeffrey Haas <[email-masked]>
Date: Mon, 8 Apr 2002 18:20:36 -0400

Extended communities authors:

In both the route target and route origin communities, you have
the following paragraph:

:    When the value of the Type field is 0x00 or 0x02, the value of the
:    Local Administrator sub-field in the Value Field MUST be unique
:    within the Autonomous system carried in the Global Administrator sub-
:    field.

This probably should read "When the value of the high order octet of
the Type field..."

In general, what property of uniqueness is meant here?

Consider the route target community.  The route target community is 
defined as:

:    The Route Target Community identifies one or more routers that may
:    receive a set of routes (that carry this Community) carried by BGP.

By this definition, one or more routers may be addressed by a given
route target's local administrator field for a given AS in the global
administrator field.  What is meant by "unique" in this context?

The same question applies to the route origin community.

My archives (although potentially incomplete) show other people asking
this question as well:  How should extended communities deal with
aggregation?

A good case can probably be made to disallow aggregation of
routes with dissimilar route target and route origin sets.

I'm not certain it makes sense to ever include link bandwidth within
an aggregate.

Under operations:
:    A BGP speaker should not propagate a non-transitive extended
:    community across the Autonomous system boundary.

What about confederation boundaries?

-- 
Jeff Haas 
NextHop Technologies

---

From: Yakov Rekhter <[email-masked]>
Date: Tue, 09 Apr 2002 11:02:43 -0700

Jeff,

Based on the discussion with the rest of the co-authors...

> This probably should read "When the value of the high order octet of

Yes, this is correct. We'll fix it.

> administrator field.  What is meant by "unique" in this context?

The 'local administrator' field does not "address" any routers. It simply 
provides a mechanism for guaranteeing uniqueness of the community. 

> The same question applies to the route origin community.

Ditto.

> this question as well:  How should extended communities deal with

It is a matter of policy.

> I'm not certain it makes sense to ever include link bandwidth within

ditto.

> What about confederation boundaries?

My take on this would be to allow propagation across confed boundaries.

Yakov.

---

From: Jeffrey Haas <[email-masked]>
Date: Tue, 9 Apr 2002 14:52:37 -0400

Yakov,

> provides a mechanism for guaranteeing uniqueness of the community. 

Again, what do you mean by "uniqueness"?
I think what you mean is implied by an earlier portion of the document:
"...ensuring that communities can be assigned for a plethora of
 uses, without fear of overlap."

Perhaps an example would clarify things.

[Aggregation]
> It is a matter of policy.

Could you note this in the document?

> My take on this would be to allow propagation across confed boundaries.

I would too.  Could you add this to the document?

-- 
Jeff Haas 
NextHop Technologies

---

From: Jeffrey Haas <[email-masked]>
Date: Tue, 9 Apr 2002 15:26:27 -0400

On Tue, Apr 09, 2002 at 03:11:13PM -0400, Dan Tappan wrote:
> uniqueness
> 
> n : the quality of being one of a kind; "that singularity distinguished him 
> from all his companions" [syn: singularity]
> Source: WordNet ® 1.6, © 1997 Princeton University

Given this, consider a route target of type 0x00.  It has the
properties of an AS of 65534 and a Local Administrator value of 0xffffffff.
How is 0xffffffff unique within AS 65534?  

> "ensure that values for these particular extended communities can be 
> assigned in a distributed manner without fear of overlap"

Or perhaps, "The local administrator field must have a well defined
and consistant meaning throughout the domain defined by the global
administrator value"?

-- 
Jeff Haas 
NextHop Technologies

---

From: Jeffrey Haas <[email-masked]>
Date: Tue, 9 Apr 2002 16:57:12 -0400

On Tue, Apr 09, 2002 at 03:50:28PM -0400, Dan Tappan wrote:
> Are you concerned by the fact that AS 65534 is from the private space?

No.

> "in order for the community value to be unique the local administrator 
> value must be uniquely assigned by the entity or entities allocating values 
> with a given global administrator value".
> 
> But it is really necessary to spell that out?

I would say yes, but ONLY if you're keeping the "uniqueness" paragraph
for Route Origin and Target.  I'd be just as happy to have those
paragraphs deleted.

BTW:
"Two extended communities are declared equal only when [the] entire
 8 octets are equal"

(note correction).

> I guess I'm not sure what 
> your concern is:
> - multiple assigners using the same GA value?
> - A single assigner failing to keep track of which LA values have been 
> assigned?
> 
> How is this different from any other number assignment problem- e.g. IP 
> addresses?
> 
> 
> 

-- 
Jeff Haas 
NextHop Technologies

---

From: Yakov Rekhter <[email-masked]>
Date: Wed, 10 Apr 2002 14:27:14 -0700

Jeff,

> for Route Origin and Target.  I'd be just as happy to have those

How about replacing in both Section 6 and 7:

   When the value of the Type field is 0x00 or 0x02, the value of the
   Local Administrator sub-field in the Value Field MUST be unique
   within the Autonomous system carried in the Global Administrator sub-
   field.

with the following:

    When the value of the Type field is 0x00 or 0x02, the Local
    Administrator sub-field contains a number from a numbering
    space which is administered by the organization to which the
    ASN carried in the Global Administrator subfield has been
    assigned by an appropriate authority.

    When the value of the Type field is 0x01, the Local Administrator
    sub-field contains a number from a numbering space which is
    administered by the organization to which the IP address carried
    in the Global Administrator subfield has been assigned by an
    appropriate authority.

Yakov.

---

From: Jeffrey Haas <[email-masked]>
Date: Wed, 10 Apr 2002 17:31:42 -0400

>     in the Global Administrator subfield has been assigned by an

This would work.

It'd also be just as good to say (excerpted):

The Local
Administrator sub-field contains a number from a numbering
space which is administered by the organization to which the
Global Administrator subfield has been
assigned by an appropriate authority.

-- 
Jeff Haas 
NextHop Technologies