On Mon, 8 Oct 2007, Patrick W. Gilmore wrote:
If you went ahead and did this, the more specific route being announced by
you on behalf of your customer would be more likely to attract traffic back
to you. Prefix length is checked in the BGP route selection process before
AS path length. This would work in normal "everything works fine"
situations, but when things break, troubleshooting the source of the
customer's reachabilit woes will get very interesting.
You have made an assumption that the original upstream would not originate a
prefix equivalent to the one you are originating.
Internally or externally? A /24 would exist in the provider's IGP to
point traffic to that customer.
Off the top of my head, I don't see why the provider who holds the parent
block would do this externally. If the provider has, say, a /18 and they
assign a /24 of that to this customer, there would be no legitimate
reason to originate that /24 and propagate it out to the rest of the
Internet. Note that I don't consider breaking that /18 up into 64 /24s
and announcing them all separately to accomplish some sort of poor-man's
traffic engineering to be a legitimate reason :)
jms
