North American Network Operators Group

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RE: Pitfalls of annoucing /24s

  • From: H. Michael Smith, Jr.
  • Date: Wed Oct 15 17:30:26 2003

What about the /24's that many ISPs (especially tier 2-3) are assigning
to multi-homed customers?  What about an IX or "critical infrastructure
providers" that may be issued a /24 from ARIN (Policy 2001-3)? 

Although it may be rare that a large aggregate would become unreachable
to a "large" network, doesn't the possibility exist that a customer with
a /24 would become unreachable (to some) due to the aggregate dropping
out even though the /24 should still be reachable?  That scenario may
not be very likely, but the question of assymetric routing and one's
ability to balance traffic become issues.  Assigning a lower preference
to /24's would be a lot friendlier than just throwing them away.

If I am way off base, I fully expect to be corrected (with volume).  My
flame retardant suit is in place.


-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of
Phil Rosenthal
Sent: Wednesday, October 15, 2003 4:47 PM
To: John Palmer
Cc: [email protected]
Subject: Re: Pitfalls of annoucing /24s

That's how Verio does it, and I assume, that's how most people who 
filter by length do it as well.

On Oct 15, 2003, at 4:40 PM, John Palmer wrote:

> Good question.
> You know there are thousands of legacy /24's out there that were 
> allocated by
> IANA as /24's How can you aggregate them up if all you have is the
> To those who filter out /24's - how is this done - just by the netmask

> size?
> ----- Original Message -----
> From: "Jean-Christophe Smith" <[email protected]>
> To: <[email protected]>
> Sent: Wednesday, October 15, 2003 15:34
> Subject: Pitfalls of annoucing /24s
>> In current practice would there be serious jeopardy of portions of
>> internet not being able to reach this address space due to bgp 
>> filters or
>> other restrictions? What is the smallest acceptable block of IPs that

>> can be
>> announced without adverse or unpredictable results? Verio would most 
>> likely
>> be picking up these routes from us. I don't want to cause a religious
>> debate, but I am interested in what the industry consensus is.
>> I'm just doing some research, any comments would be appreciated.
>> Thanks,
>> Jean-Christophe Smith
--Phil Rosenthal
ISPrime, Inc.