Re: BYOIP and AS prepend in AWS

[Giorgio Bonfiglio via NANOG <nanog () lists nanog org>]

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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