Excellent suggestion to advertise a more specific block at the Primary
Datacenter and a less specific block at the Backup DC.
I can't get a /20, but I can justify a /23.
With that I can advertise, for example:
192.168.0.0/24 at the PDC
192.168.0.0/23 at the BDC
If the PDC advertisements fail due to a disaster/failure the less
specific /23 will route to the BDC.
Question for NANOG:
If I advertise a /24 and /23, are you aware of any ISPs that would drop
the /24 advertisement but keep the /23. If that were to happen, I could
get some traffic sent to the BDC? Or would it be ok as my direct peer
ISP wont (shouldn't) drop the /24?