Typically you only want to annouce subnets of your /18 if:
1) they represent pieces of your address space that will be multi-homed
differrently than the entire block.
2) your network and upstream providers are geographically dispersed and
you need be able to maintain connectivity to City A and City B,
even if your internal connection(s) are down.
The quesion is pragmatic, a small ISP or web-farm might never need/want
to announce subnets, a larger ISP picks up multi-homedcustomer that need
to be annouched as subnets to permit inbound traffic sharing or ends
up with transit provider A in one city and B in another, yet can't
justify a separate alloction for the new city.
Overall, the goal is a few subnets as practical and the less specific
the better. You won't be able to advertise anything more specific
than a /24 to the general internet in any case.
George
This archive was generated by hypermail 2b29 : Sun Aug 04 2002 - 04:12:27 EDT