[35552] in North American Network Operators' Group
Prefix length filtering at the ISP-ISP edge
daemon@ATHENA.MIT.EDU (Alexandre.Gibouin@sita.int)
Tue Mar 13 08:42:23 2001
From: Alexandre.Gibouin@sita.int
To: nanog@merit.edu
Message-ID: <41256A0E.004AF3E6.00@nice1.nce.sita.int>
Date: Tue, 13 Mar 2001 14:38:40 +0100
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Nothing new in this mail but I need some clarification ...
- To my understanding, the common practice is, at least, to accept any address
block larger or equal to /19 and to filter any block smaller than /24 (except
eventually at the customer-ISP edge). ARIN and RIPE have changed for a while
their minimum allocation size to /20 so I guess there is no risk of routing
blackhole with /20 blocks, right?
- What about PI-blocks between 21 and 24 bits? If a end-user network annouces
such an address block, what is the risk of routing blackholes throughout the
Internet?
- Each ISP seems to apply its own filtering policy. Nevertheless, what are the
most common filtering practices for the ISP-ISP edge?
- Is it common to have different filtering policies depending on the address
ranges?
I will be grateful for any link to official or non-official documentation.
Thanks for your help
Alex
