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
