Re: Multi-homing small ISP
At 03:14 PM 2/26/2000 -0500, Chris Wagner wrote:
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
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