[ppml] ppml 2002-7

[Forrest]

On Tue, 11 Feb 2003, CJ Wittbrodt wrote:

> 
>     
>     >
>     > There is little credible engineering reason to deny allowing an
>     > organization to own a small public block.  I have not seen any research
>     > done that would suggest that doing this would impact routing table size.
>     
>     The routing table size isn't really the main argument against this.  It's 
>     the _structure_ of the routing table, in terms of ability to aggregate.
>     
>     Right now, ARIN only allocates /20 and longer blocks.  This means that 
>     service providers could filter routes they receive on this boundary (in 
>     ARIN blocks anyway) to help control the size of the routing table in their 
>     network.  If ARIN allocates longer blocks, this ties the hands of service 
>     providers.
> 
> Don't you mean ARIN allocates /20 or shorter length blocks?  
> 
> Anyway, I have been doing some work with some students at UCLA.  The current
> results say that around 48% of allocated blocks are advertised identically 
> to how they're allocated (same prefix length, not fragments).  Around
> 40% of the allocated blocks are advertised in one or modes of fragmentation
> (combinations of aggregates and fragments). This means that an ISP could
> get great benefit from being able to filter out the fragments of shorter
> provider blocks.   I am presenting this at NANOG so fee free to look at my 
> slides.
>     
> ---CJ
> 

To me, it seems that the biggest issue that 2002-7 seems to address is 
trying to multihome small blocks that aren't located in the old Class C 
space.  It seems that most providers that do filtering, they filter on the 
old Class boundries.  In the old Class C space, they'll accept /24's 
because of people using old swamp space.  So suppose you have block 
192.0.0.0/23, your block won't likely get filtered, but suppose you have 
12.100.100.0/23, what good is it to multihome if nobody would accept your 
small route?  Basically it makes sense to allocate a specific block just 
for small organizations that want to multihome, that providers will 
accept /24's and shorter from (allocate it from the old Class C range and 
I doubt anyone will have to adjust their filters).  I just don't see this 
causing the routing table to explode in size.  What's exploding the 
routing table is stuff like someone announcing a /18 as 64 /24's (look at 
205.145.0.0).

Forrest