On Jun 4, 2012, at 6:11 PM, Jeroen Massar wrote:
On 2012-06-04 17:57, Owen DeLong wrote: [..]
If you're going to redesign the header, I'd be much more interested in having 32 bits for the destination ASN so that IDR can ignore IP prefixes altogether.
One can already do that: route your IPv6 over IPv4.... IPv4 has 32bit destination addresses remember? :)
It is also why it is fun if somebody uses a 32-bit ASN to route IPv4, as one is not making the problem smaller that way. ASNs are more used as identifiers to avoid routing loops than as actual routing parameters.
Greets, Jeroen
While this is true today (to some extent), it doesn't have to always be true. If we provided a reliable scaleable mechanism to distribute and cache prefix->ASN mappings and could reliably populate a DEST-AS field in the packet header, stub networks would no longer need separate ASNs to multihome and IDR routing could be based solely on best path to the applicable DEST-AS and we wouldn't even need to carry prefixes beyond the local AS border. While I don't think DNS is up to the task of reliable distribution and caching (though something somewhat similar to DNS could do the job rather well), DNS-style resource records could be used. For example, instead of using my own AS1734 as I do today, my multi-homed household could be placed in the database with pointers to my two upstream ASNs as follows: 2620:0:930::/48 AS 10 6939 AS 10 8121 192.124.40.0/23 AS 10 6939 AS 10 8121 192.159.10.0/24 AS 10 6939 AS 10 8121 Or, if I wanted to do some traffic engineering, I could tweak the preferences to be non-equal values. The router doing the DEST-AS insertion into the packet would grab the most preferred AS to which it has a valid feasible successor. I believe that the number of transit autonomous systems on the planet is much smaller than the minimum number of prefixes to represent all multi-homed organizations with independent routing policies. As such, I believe this could produce much more scalable routing with relatively little additional overhead. Owen