Emergency backup for a small net

This brings up a problem I have been trying to solve for a while that I have
not found an answer to. A company with an old style Class B (/16) wants to
be multihomed and split their incoming load between 2 ISPs (outgoing they
can live with going via 1 and if the primary fails they fallback to the
secondary conenction). In order to split the load on incoming, one ISP has
to announce a /17 and the other ISP has to announce a /17 (or even the
entire /16). But since this net is from the 147.x.x.x range, various ISPs
around the globe will filter out the /17. This means that having a /16 from
the 192.x.x.x range is better (these days), unless someone can show me a


Couldn't/wouldn't you just be able to BGP announcement the /16 to both
providers and if one gets a little too well announced [i.e. not even
split] unsweeten it with a higher metric?

The idea of splitting a /16 into two /17s for the sole purpose of getting
two providers is a little shaky in my world it strikes me as twice as
vulnerable to outage.

You *could* announce the same /16 to both upstreams and then 1 of the two
/17s to [each] to the two providers [as a more specific route] -- if they
take it, great, if they don't you are still covered with the /16.



since RIPE has been assigned and RIPE started to assign
allocations ranging between /16 to /19 to Local Internet Registries (i.e.
ISPs) througout Europe, the problem regarding filtering prefixes greater
than /16 out of the Class A range will be addressed fairly soon, I guess.