Hey Hank,

> Can someone explain to me how to BYOIP into AWS and use AS prepends?

are you referring to prepending your AS (once) to AS16509 or prepending your AS 
/ AS16509 a number of times to steer traffic?

The first one can be done through BYOASNs in IPAM - ref: 
https://docs.aws.amazon.com/vpc/latest/ipam/tutorials-byoasn.html.

The second isn’t strictly possible, but you can control whether your prefixes 
are advertised or not via:
- 
https://awscli.amazonaws.com/v2/documentation/api/latest/reference/ec2/advertise-byoip-cidr.html
- 
https://awscli.amazonaws.com/v2/documentation/api/latest/reference/ec2/withdraw-byoip-cidr.html

If your plan was to use prepending to control whether your traffic goes to AWS 
or somewhere else for some sort of disaster recovery, you can achieve something 
very similar with the two commands/APIs above at the cost of a slightly higher 
convergence time. These two operations can be automated through a range of 
health checks.

The only config which can’t be easily replicated is where you would use prepend 
on both sides to steer traffic away from primary location in case it stays up 
but you lose management/control (2x prepend on primary, 3x prepend on secondary 
- secondary can attract traffic by flipping to 1x prepend) but I haven’t seen 
it used in a looong time.

Giorgio
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