Subject: Review of draft-ietf-idr-bgp4-17.txt-advertise inactive

From: "Natale, Jonathan" <[email-masked]>
Date: Fri, 13 Sep 2002 18:42:48 -0400

I propose changing:
"To characterize the set of policy decisions that can be enforced
   using BGP, one must focus on the rule that a BGP speaker advertises
   to its peers (other BGP speakers which it communicates with) in
   neighboring ASs only those routes that it itself uses."

To:
"To characterize the set of policy decisions that can be enforced
   using BGP, one must focus on the rule that a BGP speaker advertises
   to its peers (other BGP speakers which it communicates with)
   only those prefixes that it itself uses. Whether or not to require the
prefixes be used itself by virtue of a bgp learned route MAY be an
administratively configurable option."

Since:
1) This rule applies to IBGP as well as to EBGP. 
2) The prefix need not necessarily be in the local routing table via bgp.
3) Juniper has a advertise inactive concept, Cisco does not.
4) The term route (vs prefix) is defined to include the attributes which
means that Cisco is non-compliant (in that it will advertise a route if the
route's prefix is installed via another protocol), and juniper may be
configured to be non-compliant (turning off advertise inactive).

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From: Yakov Rekhter <[email-masked]>
Date: Sat, 14 Sep 2002 19:18:53 -0700

Jonathan,

> configured to be non-compliant (turning off advertise inactive).

The original text (and I think your replacement text as well) is
a bit broken as it doesn't cover the case of the "third-party" Next
Hop.

The *real* issue that the text you mentioned above is trying to
capture (although it clearly didn't capture it well enough) is that 
BGP is built to support the destination-based forwarding paradigm.

So, with this in mind I would suggest to replace

   To characterize the set of policy decisions that can be enforced
   using BGP, one must focus on the rule that a BGP speaker advertises
   to its peers (other BGP speakers which it communicates with) in
   neighboring ASs only those routes that it itself uses. This rule
   reflects the "hop-by-hop" routing paradigm generally used
   throughout the current Internet. Note that some policies cannot
   be supported by the "hop-by-hop" routing paradigm and thus
   require techniques such as source routing (aka explicit routing)
   to enforce. For example, BGP does not enable one AS to send
   traffic to a neighboring AS intending that the traffic take a
   different route from that taken by traffic originating in the
   neighboring AS. On the other hand, BGP can support any policy
   conforming to the "hop-by-hop" routing paradigm. Since the
   current Internet uses only the "hop-by-hop" inter-AS routing
   paradigm and since BGP can support any policy that conforms to
   that paradigm, BGP is highly applicable as an inter-AS routing
   protocol for the current Internet.

with the following:

   Routing information exchanged via BGP supports only the
   destination-based forwarding paradigm, which assumes that a
   router forwards a packet based solely on the destination address
   carried in the IP header of the packet. This, in turn reflects
   the set of policy decisions that can (and can not) be enforces
   using BGP. Note that some policies cannot be supported by the
   destination-based forwarding paradigm and thus require techniques
   such as source routing (aka explicit routing) to enforce. Such
   policies can not be enforced using BGP either. For example, BGP
   does not enable one AS to send traffic to a neighboring AS
   intending that the traffic take a different route from that
   taken by traffic originating in the neighboring AS.  On the
   other hand, BGP can support any policy conforming to the
   destination-based forwarding paradigm.

Yakov.

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From: Curtis Villamizar <[email-masked]>
Date: Wed, 18 Sep 2002 15:53:42 -0400

In message <[email-masked]>, Yakov Rekhter writes
>    destination-based forwarding paradigm.

The replacement paragraph is much more clear.

Curtis