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

From: "Tom Petch" <[email-masked]>
Date: Mon, 16 Sep 2002 14:53:06 +0100

I prefer Yakov's formulation but suggest turning the long sentence
around thus:
(! denotes changed text).

     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 enforced*
     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 be enforced*.
Such
     policies can not be enforced using BGP either. For example,
     BGP does not enable one AS to send traffic
!    to a neighboring AS for forwarding to some destination (reachable
through but) beyond
!    that neighboring AS intending that
!    the traffic take a different route to that taken by the traffic
!    originating in the neighboring AS (for that same destination).

     On the other hand, BGP can support any policy conforming to
     the destination-based forwarding paradigm.

Tom Petch
[email-masked]

-----Original Message-----
From: Martin, Christian <[email-masked]>
To: 'Yakov Rekhter' <[email-masked]>; Martin, Christian
<[email-masked]>
Cc: [email-masked]' <[email-masked]>
Date: 15 September 2002 21:03
Subject: RE: Review of draft-ietf-idr-bgp4-17.txt-advertise inactive

>Yakov,
>
>I see what you are trying to say, but it took me a few reads.  What
we are
>saying is that BGP policy local to an AS cannot affect a path that a
>neighboring AS uses to continue downstream.  This is hard to say in
any
>succinct way, and the sentence is pretty long.
>
>Maybe something like this:
>
>    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 through a neighboring
>    AS to some destination beyond the neighboring AS intending that
>    the traffic take a different route from that taken by traffic
>    to the same destination which originates in the neighboring AS.
>    In other words, the BGP policy of a local AS cannot affect the
>    downstream (aka, away from the local AS) forwarding policy of a
>    remote AS.  On the other hand, BGP can support any policy
conforming
>    to the destination-based forwarding paradigm.
>
>-chris
>
>> -----Original Message-----
>> From: Yakov Rekhter [mailto:[email-masked]]
>> Sent: Sunday, September 15, 2002 3:25 PM
>> To: Martin, Christian
>> Cc: Natale, Jonathan; [email-masked]'
>> Subject: Re: Review of draft-ietf-idr-bgp4-17.txt-advertise
inactive
>>
>>
>> Martin,
>>
>> > Yakov,
>> >
>> > In both examples below, it would appear that BGP does not have
the
>> > capability to affect asymmetric routing, which it clearly
>> does as is
>> > evidenced by traffic on the Internet today.  Perhaps it
>> would be more
>> > clear to use an example that is more congruent with the
>> > destination-based vs source-based argument you are making.
>> >
>> > IE:
>> >
>> >    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
>> >    based on prefixes originating from the local AS.  On the
>> >    other hand, BGP can support any policy conforming to the
>> >    destination-based forwarding paradigm.
>>
>> How about 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 through a
neighboring
>>     AS to some destination (which is outside of the neighboring
>>     AS, but is reachable through the neighboring AS) intending that
>>     the traffic take a different route from that taken by the
traffic
>>     to the same destination that originating in the neighboring AS.
>>     On the other hand, BGP can support any policy conforming to
>>     the destination-based forwarding paradigm.
>>
>> Yakov.
>>

---

From: Yakov Rekhter <[email-masked]>
Date: Mon, 16 Sep 2002 18:55:22 -0700

Tom,

>      the destination-based forwarding paradigm.

The changes you proposed are fine.

Yakov.