10 Dec
2015
10 Dec
'15
12:34 p.m.
Marius:
Coming back to the IP range/AS assignment:
IMHO there must and shall not be such a correspondence. An AS is used to
group one or more subnets into an well, Autonomous System (AS), and it
should support, based on network architecture and layout, a possible
migration of subnets from/to a specific AS, without any changes in the
peering structure.
e.g. If there is a subnet with access via AS 1 it should be there. But if
later this subnet will be reorganized, and lets say will be accessed via AS
2, it should be possible to move it to AS 2 without any change in the BGP
peering. This is not possible using AS numbers generated from IPs.
The idea behind using the IP address to calculate the AS is to make sure
that AS numbers are always unique, without having to use a registry and without
having to coordinate. When there is more than one subnet, it does not matter
which one is used to calculate the AS number. When the one that was used to
calculate the AS is being moved, some care will be required so it is not used
again for this purpose at the new site.
Up to now we only route to the "regional subnet" level and each region has only
a single subnet, so there are no problems. If an additional subnet is added
and then the original one is moved there could be problems, but this is not
likely.
This whole thing can depend on local issues and policies, but it does not
really matter how you do things locally as long as everyone uses the same
method to generate the prefix of the number. I will stick to that E.212
thing as it uses only 3 digits and because others are already doing this.
(if not, I would probably have removed the "44" digits and added 2 available
digits at the end, as proposed by Robbie)
Rob