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Beginner

Big prefix block separation to different public AS's. How to anounce?

Hello everyone and happy new year

This question is in some way related to https://supportforums.cisco.com/message/3806616

Imagine AS65200 anouncing block 10.10.0.0/22 to the internet.

Now for some reason we need to announce block 10.10.2.0/24 from AS65333.

How should routes from AS65200 be announced now?

  • Can I maintain the whole /22 block since 10.10.2.0/24 from AS65333 is more specific?
  • Or should I now break AS65200 announcement into smaller prefixes completelly excluding .2.0/24 ?( .0.0/23 and .3.0/24)

Thanks all

Mario

                 
10.10.10.0/22
     (AS65200)


10.10.10.0/23   (AS65200)
10.10.2.0/24 (AS65333)
10.10.3.0/24 (AS65200)
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Hall of Fame Mentor

Big prefix block separation to different public AS's. How to ano

As you stated, the /24 is more specific and traffic going to that subnet will use AS 65333

Other subnets from the /22 will use AS 65200

Regards,

Beginner

Big prefix block separation to different public AS's. How to ano

Mario,

If you are peering with the same upstream, you can advertise the whole /22 via AS65200  and only advertise a /24 via AS65333. The /24 is more prefered at all times until your link goes down.

If you peer with more then one upstream, that you will need to make some fun changes...

Beginner

Big prefix block separation to different public AS's. How to ano

Ahad,

We are from completely different upstream (different continents even) what are these fun changes?

Mario

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