Philip,
My interpretation of "generally should belong to one AS" does not equate to "MUST NOT be announced by more than one AS".
Not commenting on the rights and wrong, but if this is really a "MUST NOT" it needs to be documented as such.
Somewhere in Basham Halabi's "Internet Routing Architectures" (Cisco Press) he mentions that two different origins for a prefix is an "illegal configuration". Unfortunately I just can't find the exact phrase in the book. Anyway, I am sure that announcing the same prefix under 2 different origins should work although I never did something like this.
philip
Let's further discuss this at ripe-37. Regards, Sascha
--
At 02:59 01/09/00 +0900, Randy Bush wrote:
The only thing that is definitely not allowed due to bgp4-specifications is to announce the same prefix from different origin-ASes.
this is not bgp spec. it is rfc 1930, see appended, and is not a MUST NOT.
randy
7. One prefix, one origin AS
Generally, a prefix can should belong to only one AS. This is a direct consequence of the fact that at each point in the Internet there can be exactly one routing policy for traffic destined to each prefix. In the case of an prefix which is used in neighbor peering between two ASes, a conscious decision should be made as to which AS this prefix actually resides in.
With the introduction of aggregation it should be noted that a prefix may be represented as residing in more than one AS, however, this is very much the exception rather than the rule. This happens when aggregating using the AS_SET attribute in BGP, wherein the concept of origin is lost. In some cases the origin AS is lost altogether if there is a less specific aggregate announcement setting the ATOMIC_AGGREGATE attribute.
--- Sascha E. Pollok Internet Port Hamburg Technical Staff / Network Operations Grosse Reichenstrasse 27 D-20457 Hamburg Germany Tel.�� +49 (0)40 37 49 19-0 Fax��� +49 (0)40 37 49 19-29 Email: sp@iphh.de ICQ #38955239