What is the most standard subnet length on internet

[lionair at samsung.com (ChiYoung Joung)]

I would like to ask question more specifically.

I know most of tier1 providers accept their customer prefixes smaller than /24.
it means smaller than /24 routes always routable in that Tier1 provider.
What about between Tier1 and another Tier1 ?  
Do they exchange their full customer's routes without any limitation of prefixes length ?
or do they refer to some DB information like Regional Internet Registry and 
apply another filter on neighbor configuration with another Tier1 ?  

Chiyoung
=============================================
 Chi-Young Joung
 SAMSUNG NETWORKS Inc.
 Email: lionair at samsung.com
 Tel +82 70 7015 0623, Mobile +82 17 520 9193
 Fax +82 70 7016 0031
=============================================

------- Original Message -------
Sender : Nathan Ward<nanog at daork.net> 
Date   : 2008-12-23 10:44 (GMT+09:00)
Title  : Re: What is the most standard subnet length on internet

On 23/12/2008, at 2:39 PM, Joe Provo wrote:

> On Tue, Dec 23, 2008 at 02:34:39PM +1300, Nathan Ward wrote:
> [snip]
>> Let me rephrase; Are there people who are filtering /24s received  
>> from
>> eBGP peers who do not have a default route?
>
> of course.


Curiously, it was really meant as a rhetorical question where the  
answer was "no".

Why are people doing this? Are they lacking clue, or, is there some  
reasonable purpose?

--
Nathan Ward