At 12:44 PM 2/26/00 -0700, Nate Duehr wrote: >You don't have to have your own IP space from ARIN to have another ISP >route your /24. BGP handles this fine. Just negotiate with the second
I know that can be done but what is the minimum block size ISP's will route? I've heard of some nationals not wanting to route even full class C's. What about a situation where a place had two /27's from different ISPs? I think any place would balk at adding a route for a measely /27. Having one pipe for outbound and the other for inbound might be a solution. Or possibly some kind of address translation to load balance between the two pipes, like say IP over IP encapsulation. Small block routing has always been a sticky wicket.
Certain providers (e.g. Sprintlink and Digex) reportedly filter anything smaller that /18 from non customers. I think these outfits do advertise /24's for customers. Hence if you have an ASN and provider allocated /24, chances are that your advertisements are going to get filtered. The provider who allocated the IP's can include your block in a larger aggregate and advertise them that way. You second provider cannot do this though. Makes load balancing, etc. a sticky wicket. Bottom line is that you want to get the largest block of *contiguous* IP's you can reasonably justify. Anyhow, I'm far from expert on this, and here's a response I got from another list to a similar querry:
Partly that depends on if provider #1 is filtering your more specific advertisement. If the do NOT, then the following occurs:
Any networks not filtering will see both routes through both providers and choose closer
Any networks filtering will see only the aggregate route and send the packet to provider #1
If they DO filter outgoing advertisements then the following, weirder thing happens:
Any network that is not filtering will see the more specific route from #2 and choose it over the aggregate route (more specific routes are preferred)
Any network that does not see that more specific route will route to the aggregate route in #1.
HTH- Ken
