Upstreams blocking /24s? (was Re: How Not to Multihome)

Tue Oct 9 03:14:44 UTC 2007

On Oct 8, 2007, at 10:28 PM, David Conrad wrote:

> The argument, as I understand it (and those who argue this  
> direction feel free to correct me if I misstate), is that as the  
> IPv4 free pool exhausts, there will be a natural pressure to  
> increase address utilization efficiency.  This will likely mean  
> longer prefixes will begin to be put (back) into use, either from  
> assignments and allocations that were "rediscovered" or from unused  
> portions of shorter prefixes.  Customers will approach ISPs to get  
> these long prefixes routed, shopping through ISPs until they find  
> one that will accept their money and propagate the long prefix.
>
> Now, of course announcing a route doesn't mean anyone will accept  
> it, but as I understand the theory, larger ISPs will agree to  
> accept and propagate longer prefixes from other larger ISPs if  
> those other ISPs will be willing to accept and propagate  
> transmitted long prefixes ("scratch my back and I'll scratch  
> yours"), particularly if this encourages the smaller ISPs to 'look  
> for other employment opportunities' when they can't afford the  
> router upgrades.

We know this is not the case from history.  For instance, look at  
Sprint & ACL112.

Also, we know from history that smaller ISPs sometimes are better  
able to do router upgrades than large ones.

> Personally, I fully expect the first part to happen.  Where I'm  
> having trouble is the second part (the accepting longer prefixes  
> part).  However, a few prominent members of the Internet operations  
> community whom I respect have argued strongly that this is going to  
> happen.  I thought I'd ask around to see what other folk think...

I'd bet against the first part happening, so the second part is moot.

-- 
TTFN,
patrick