On 7-jul-04, at 22:39, Fred Baker wrote:
When a company changes providers, it is common to institute an overlap
period, during which it is served by both providers. By definition, the
network is multihomed during such a period. While this document is not
about multihoming per se, problems can arise as a result of ingress
filtering policies applied by the upstream provider or one of its
upstream providers, so the user of this document need also be cognizant
of these issues. This is discussed in detail, and approaches to dealing
with it are described, in [RFC2827] and [RFC3704].
These references outline ingress filtering, but there is only about half a
page in the second one about how to route traffic with certain addresses
to a certain provider, and this half page provides very little actual guidance.
A few paragraphs along the lines of "ask one ISP to temporarily accept
packets with the other's addresses and use that one for outgoing traffic
or use policy routing to match ISPs to the source addresses in outgoing
packets, or if these approaches aren't possible, implement a flag-day type
of transition" would be very helpful, I think.