On 21-mrt-2007, at 14:45, Curtis Villamizar wrote:
Does this address the solution where multihomer M uses ISPs A and B,
and M's prefix is injected into BGP by both A and B and NOT by M?
I.e., "inconsistent origin AS", which is frowned upon.
If not, the text is unclear. If so, why is there no discussion of the
normal situation where the multihomed AS advertises its prefix
itself?
If normal means "architecturally pretty" then the multihomed prefix
advertised by the true oridinator is normal. No special case is
needed for that.
If you mention special cases you must also specify the normal case.
These are engineering documents, any time someone has to think about
semantics we're in trouble.
Many multihomed enterprises don't have their own AS and have a single
prefix. They don't run BGP. Instead each provider conditionally
originates the prefix on their end with their AS if the link is up.
If normal means "more common" then this might be the normal case.
Absolutely not. Last time I checked the first figure for incosistent
origin AS were less than 1000 prefixes. The nature of this practice
means you'll never see every affected prefix from any one given
vantage point but it's pretty obvious that this is NOT a common
practice.
And why sghould it be? An AS number is much easier to get than
address space and running BGP is much simpler than alternative
methods to inject/remove prefixes depending on connectivity to a
particular ISP.
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